diff --git a/crates/ghostty-os/Cargo.toml b/crates/ghostty-os/Cargo.toml
index ef24850..25836eb 100644
--- a/crates/ghostty-os/Cargo.toml
+++ b/crates/ghostty-os/Cargo.toml
@@ -5,7 +5,16 @@ edition.workspace = true
 license.workspace = true
 
 [dependencies]
+gettext-rs = { version = "0.8.0", features = ["gettext-system"] }
+log = "0.4.34"
+nix = { version = "0.31.3", features = ["user"] }
+rustix = { version = "1.1.5", features = ["fs", "process", "system", "pipe", "net", "time", "rand"] }
+thiserror = "2.0.21"
+zbus = "5.19.0"
 
 
 [lints]
 workspace = true
+
+[dev-dependencies]
+temp-env = "0.3.6"
diff --git a/crates/ghostty-os/src/args.rs b/crates/ghostty-os/src/args.rs
new file mode 100644
index 0000000..2cf10ae
--- /dev/null
+++ b/crates/ghostty-os/src/args.rs
@@ -0,0 +1,21 @@
+//! Command line argument iteration.
+//!
+//! The macOS NSProcessInfo-based iterator is skipped; on Linux this is the
+//! standard process argument iterator (as `os_str`s so that non-UTF-8 args
+//! don't panic).
+
+/// Returns an iterator over the command line arguments.
+pub fn iterator() -> std::env::ArgsOs {
+    std::env::args_os()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn args() {
+        let mut iter = iterator();
+        assert!(!iter.next().unwrap().is_empty());
+    }
+}
diff --git a/crates/ghostty-os/src/cgroup.rs b/crates/ghostty-os/src/cgroup.rs
new file mode 100644
index 0000000..dc8a214
--- /dev/null
+++ b/crates/ghostty-os/src/cgroup.rs
@@ -0,0 +1,40 @@
+use std::io::Read;
+
+/// Maximum number of bytes read from the cgroup file (the Zig version reads
+/// into a caller-provided buffer; callers there use path-sized buffers).
+const READ_LIMIT: u64 = 4096;
+
+/// Returns the path to the cgroup for the given pid.
+pub fn current(pid: u32) -> Option<String> {
+    // Read our cgroup by opening /proc/<pid>/cgroup and reading the first
+    // line. The first line will look something like this:
+    // 0::/user.slice/user-1000.slice/session-1.scope
+    // The cgroup path is the third field.
+    let file = std::fs::File::open(format!("/proc/{pid}/cgroup")).ok()?;
+    let mut contents = Vec::new();
+    file.take(READ_LIMIT).read_to_end(&mut contents).ok()?;
+
+    // Find the last ':'
+    let idx = contents.iter().rposition(|&b| b == b':')?;
+    let rest = &contents[idx + 1..];
+    let end = rest
+        .iter()
+        .rposition(|b| !matches!(b, b' ' | b'\r' | b'\n'))
+        .map_or(0, |i| i + 1);
+    Some(String::from_utf8_lossy(&rest[..end]).into_owned())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn current_cgroup_of_self() {
+        // Not part of the Zig tests; sanity check that parsing works when
+        // /proc is available.
+        if let Some(p) = current(std::process::id()) {
+            assert!(!p.ends_with('\n'));
+        }
+        assert!(current(u32::MAX).is_none());
+    }
+}
diff --git a/crates/ghostty-os/src/dbus.rs b/crates/ghostty-os/src/dbus.rs
new file mode 100644
index 0000000..131f65b
--- /dev/null
+++ b/crates/ghostty-os/src/dbus.rs
@@ -0,0 +1,36 @@
+/// Returns true if the program was launched by D-Bus activation.
+///
+/// On Linux GTK, this returns true if the program was launched using D-Bus
+/// activation. It will return false if Ghostty was launched any other way.
+pub fn launched_by_dbus_activation() -> bool {
+    // On Linux, D-Bus activation sets `DBUS_STARTER_ADDRESS` and
+    // `DBUS_STARTER_BUS_TYPE`. If these environment variables are present
+    // (no matter the value) we were launched by D-Bus activation.
+    std::env::var_os("DBUS_STARTER_ADDRESS").is_some()
+        && std::env::var_os("DBUS_STARTER_BUS_TYPE").is_some()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::testutil::with_env_lock;
+
+    #[test]
+    fn dbus_activation_env() {
+        temp_env::with_vars(
+            [
+                ("DBUS_STARTER_ADDRESS", Some("x")),
+                ("DBUS_STARTER_BUS_TYPE", Some("session")),
+            ],
+            || assert!(launched_by_dbus_activation()),
+        );
+        temp_env::with_vars(
+            [
+                ("DBUS_STARTER_ADDRESS", Some("x")),
+                ("DBUS_STARTER_BUS_TYPE", None),
+            ],
+            || assert!(!launched_by_dbus_activation()),
+        );
+        with_env_lock(|| {});
+    }
+}
diff --git a/crates/ghostty-os/src/desktop.rs b/crates/ghostty-os/src/desktop.rs
new file mode 100644
index 0000000..21e1ed1
--- /dev/null
+++ b/crates/ghostty-os/src/desktop.rs
@@ -0,0 +1,112 @@
+/// Returns true if the program was launched from a desktop environment.
+///
+/// On Linux GTK, this returns true if the program was launched using the
+/// desktop file. This also includes when `gtk-launch` is used because I
+/// can't find a way to distinguish the two scenarios.
+pub fn launched_from_desktop() -> bool {
+    // On Linux and BSD, GTK sets GIO_LAUNCHED_DESKTOP_FILE and
+    // GIO_LAUNCHED_DESKTOP_FILE_PID. We only check the latter to see if
+    // we match the PID and assume that if we do, we were launched from
+    // the desktop file. Pid comparing catches the scenario where
+    // another terminal was launched from a desktop file and then launches
+    // Ghostty and Ghostty inherits the env.
+    let Some(gio_pid_str) = std::env::var_os("GIO_LAUNCHED_DESKTOP_FILE_PID") else {
+        return false;
+    };
+
+    let pid = rustix::process::getpid().as_raw_nonzero().get();
+    let Ok(gio_pid) = gio_pid_str.to_string_lossy().parse::<i32>() else {
+        return false;
+    };
+
+    gio_pid == pid
+}
+
+/// The list of desktop environments that we detect. New Linux desktop
+/// environments should only be added to this list if there's a specific reason
+/// to differentiate between `gnome` and `other`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DesktopEnvironment {
+    Gnome,
+    Macos,
+    Other,
+    Windows,
+}
+
+/// Detect what desktop environment we are running under. This is mainly used
+/// on Linux and BSD to enable or disable certain features but there may be more uses in
+/// the future.
+pub fn desktop_environment() -> DesktopEnvironment {
+    // Use $XDG_SESSION_DESKTOP to determine what DE we are using on Linux
+    // https://www.freedesktop.org/software/systemd/man/latest/pam_systemd.html#desktop=
+    if let Some(sd) = std::env::var_os("XDG_SESSION_DESKTOP") {
+        let sd = sd.to_string_lossy();
+        if sd.eq_ignore_ascii_case("gnome") {
+            return DesktopEnvironment::Gnome;
+        }
+        if sd.eq_ignore_ascii_case("gnome-xorg") {
+            return DesktopEnvironment::Gnome;
+        }
+    }
+
+    // If $XDG_SESSION_DESKTOP is not set, or doesn't match any known
+    // DE, check $XDG_CURRENT_DESKTOP. $XDG_CURRENT_DESKTOP is a
+    // colon-separated list of up to three desktop names, although we
+    // only look at the first.
+    // https://specifications.freedesktop.org/desktop-entry-spec/latest/recognized-keys.html
+    if let Some(cd) = std::env::var_os("XDG_CURRENT_DESKTOP") {
+        let cd = cd.to_string_lossy();
+        let first = cd.split(':').next().unwrap_or("");
+        if first.eq_ignore_ascii_case("gnome") {
+            return DesktopEnvironment::Gnome;
+        }
+    }
+
+    DesktopEnvironment::Other
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn de(session: Option<&str>, current: Option<&str>) -> DesktopEnvironment {
+        temp_env::with_vars(
+            [
+                ("XDG_SESSION_DESKTOP", session),
+                ("XDG_CURRENT_DESKTOP", current),
+            ],
+            desktop_environment,
+        )
+    }
+
+    #[test]
+    fn desktop_environment_detection() {
+        use DesktopEnvironment::{Gnome, Other};
+        assert_eq!(de(Some("gnome"), None), Gnome);
+        assert_eq!(de(Some("gnome-xorg"), None), Gnome);
+        assert_eq!(de(Some("foobar"), None), Other);
+        assert_eq!(de(None, None), Other);
+        assert_eq!(de(None, Some("GNOME")), Gnome);
+        assert_eq!(de(None, Some("FOOBAR")), Other);
+        assert_eq!(de(None, Some("GNOME:Unity")), Gnome);
+        assert_eq!(de(None, Some("Unity:GNOME")), Other);
+        assert_eq!(de(Some("foobar"), Some("GNOME")), Gnome);
+    }
+
+    #[test]
+    fn launched_from_desktop_pid_match() {
+        let pid = std::process::id().to_string();
+        temp_env::with_var("GIO_LAUNCHED_DESKTOP_FILE_PID", Some(pid), || {
+            assert!(launched_from_desktop());
+        });
+        temp_env::with_var("GIO_LAUNCHED_DESKTOP_FILE_PID", Some("1"), || {
+            assert!(!launched_from_desktop());
+        });
+        temp_env::with_var("GIO_LAUNCHED_DESKTOP_FILE_PID", Some("abc"), || {
+            assert!(!launched_from_desktop());
+        });
+        temp_env::with_var("GIO_LAUNCHED_DESKTOP_FILE_PID", None::<&str>, || {
+            assert!(!launched_from_desktop());
+        });
+    }
+}
diff --git a/crates/ghostty-os/src/env.rs b/crates/ghostty-os/src/env.rs
new file mode 100644
index 0000000..937929d
--- /dev/null
+++ b/crates/ghostty-os/src/env.rs
@@ -0,0 +1,106 @@
+use std::collections::HashMap;
+
+use crate::flatpak::is_flatpak;
+
+/// PATH-style delimiter (`std.fs.path.delimiter` on POSIX).
+const DELIMITER: char = ':';
+
+/// Get the environment map. Inside Flatpak this is empty (the sandbox
+/// environment is not meaningful for host commands).
+pub fn get_env_map() -> HashMap<String, String> {
+    if is_flatpak() {
+        return HashMap::new();
+    }
+    std::env::vars_os()
+        .map(|(k, v)| {
+            (
+                k.to_string_lossy().into_owned(),
+                v.to_string_lossy().into_owned(),
+            )
+        })
+        .collect()
+}
+
+/// Append a value to an environment variable such as PATH.
+pub fn append_env(current: &str, value: &str) -> String {
+    // If there is no prior value, we return it as-is
+    if current.is_empty() {
+        return value.to_owned();
+    }
+
+    // Otherwise we must prefix.
+    append_env_always(current, value)
+}
+
+/// Always append value to environment, even when it is empty.
+/// This is useful because some env vars (like MANPATH) want there
+/// to be an empty prefix to preserve existing values.
+pub fn append_env_always(current: &str, value: &str) -> String {
+    format!("{current}{DELIMITER}{value}")
+}
+
+/// Prepend a value to an environment variable such as PATH.
+pub fn prepend_env(current: &str, value: &str) -> String {
+    // If there is no prior value, we return it as-is
+    if current.is_empty() {
+        return value.to_owned();
+    }
+
+    format!("{value}{DELIMITER}{current}")
+}
+
+/// Gets the value of an environment variable, or None if not found
+/// (or not valid unicode).
+pub fn getenv(key: &str) -> Option<String> {
+    std::env::var(key).ok()
+}
+
+/// Gets the value of an environment variable. Returns None if not found or
+/// the value is empty.
+pub fn getenv_not_empty(key: &str) -> Option<String> {
+    getenv(key).filter(|v| !v.is_empty())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn append_env_empty() {
+        assert_eq!(append_env("", "foo"), "foo");
+    }
+
+    #[test]
+    fn append_env_existing() {
+        assert_eq!(append_env("a:b", "foo"), "a:b:foo");
+    }
+
+    #[test]
+    fn prepend_env_empty() {
+        assert_eq!(prepend_env("", "foo"), "foo");
+    }
+
+    #[test]
+    fn prepend_env_existing() {
+        assert_eq!(prepend_env("a:b", "foo"), "foo:a:b");
+    }
+
+    #[test]
+    fn append_env_always_empty_value() {
+        assert_eq!(append_env_always("a", ""), "a:");
+        assert_eq!(append_env_always("", "x"), ":x");
+    }
+
+    #[test]
+    fn getenv_not_empty_filters() {
+        temp_env::with_vars(
+            [("GHOSTTY_RS_T1", Some("")), ("GHOSTTY_RS_T2", Some("v"))],
+            || {
+                assert_eq!(getenv("GHOSTTY_RS_T1").as_deref(), Some(""));
+                assert_eq!(getenv_not_empty("GHOSTTY_RS_T1"), None);
+                assert_eq!(getenv_not_empty("GHOSTTY_RS_T2").as_deref(), Some("v"));
+                assert_eq!(getenv_not_empty("GHOSTTY_RS_NOPE"), None);
+            },
+        );
+    }
+}
diff --git a/crates/ghostty-os/src/file.rs b/crates/ghostty-os/src/file.rs
new file mode 100644
index 0000000..40e854b
--- /dev/null
+++ b/crates/ghostty-os/src/file.rs
@@ -0,0 +1,101 @@
+use rustix::process::{Resource, Rlimit as RustixRlimit, getrlimit, setrlimit};
+
+/// Resource limit (`rlimit` in Zig). `None` means infinity.
+pub type Rlimit = RustixRlimit;
+
+/// rlim_t value for infinity in the Zig implementation.
+const INFINITY: u64 = u64::MAX;
+
+fn cur(l: &Rlimit) -> u64 {
+    l.current.unwrap_or(INFINITY)
+}
+fn max(l: &Rlimit) -> u64 {
+    l.maximum.unwrap_or(INFINITY)
+}
+fn mk(cur: u64, max: Option<u64>) -> Rlimit {
+    Rlimit {
+        current: if cur == INFINITY { None } else { Some(cur) },
+        maximum: max,
+    }
+}
+
+/// This maximizes the number of file descriptors we can have open. We
+/// need to do this because each window consumes at least a handful of fds.
+/// This is extracted from the Zig compiler source code.
+pub fn fix_max_files() -> Option<Rlimit> {
+    let old = getrlimit(Resource::Nofile);
+
+    // If we're already at the max, we're done.
+    if cur(&old) >= max(&old) {
+        log::debug!("file handle limit already maximized value={}", cur(&old));
+        return Some(old);
+    }
+
+    // Do a binary search for the limit.
+    let mut lim = old;
+    let mut min_v: u64 = cur(&lim);
+    let mut max_v: u64 = 1 << 20;
+    // But if there's a defined upper bound, don't search, just set it.
+    if max(&lim) != INFINITY {
+        min_v = max(&lim);
+        max_v = max(&lim);
+    }
+
+    loop {
+        let c = min_v + (max_v - min_v) / 2;
+        lim = mk(c, lim.maximum);
+        if setrlimit(Resource::Nofile, lim).is_ok() {
+            min_v = c;
+        } else {
+            max_v = c;
+        }
+        if min_v + 1 >= max_v {
+            break;
+        }
+    }
+
+    log::debug!("file handle limit raised value={}", cur(&lim));
+    Some(old)
+}
+
+pub fn restore_max_files(lim: Rlimit) {
+    let _ = setrlimit(Resource::Nofile, lim);
+}
+
+/// Return the recommended path for temporary files.
+pub fn alloc_tmp_dir() -> Option<String> {
+    if let Some(v) = std::env::var_os("TMPDIR") {
+        return Some(v.to_string_lossy().into_owned());
+    }
+    if let Some(v) = std::env::var_os("TMP") {
+        return Some(v.to_string_lossy().into_owned());
+    }
+    Some("/tmp".to_owned())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn tmp_dir_env_precedence() {
+        temp_env::with_vars([("TMPDIR", Some("/a")), ("TMP", Some("/b"))], || {
+            assert_eq!(alloc_tmp_dir().as_deref(), Some("/a"));
+        });
+        temp_env::with_vars([("TMPDIR", None), ("TMP", Some("/b"))], || {
+            assert_eq!(alloc_tmp_dir().as_deref(), Some("/b"));
+        });
+        temp_env::with_vars([("TMPDIR", None::<&str>), ("TMP", None)], || {
+            assert_eq!(alloc_tmp_dir().as_deref(), Some("/tmp"));
+        });
+    }
+
+    #[test]
+    fn fix_and_restore_max_files() {
+        let old = fix_max_files().unwrap();
+        let now = getrlimit(Resource::Nofile);
+        assert!(cur(&now) >= cur(&old));
+        restore_max_files(old);
+        assert_eq!(getrlimit(Resource::Nofile), old);
+    }
+}
diff --git a/crates/ghostty-os/src/file_type.rs b/crates/ghostty-os/src/file_type.rs
new file mode 100644
index 0000000..db4816c
--- /dev/null
+++ b/crates/ghostty-os/src/file_type.rs
@@ -0,0 +1,194 @@
+//! Port of `src/file_type.zig`.
+
+struct TypeDetails {
+    typ: FileType,
+    sigs: &'static [&'static [Option<u8>]],
+    exts: &'static [&'static str],
+}
+
+#[allow(clippy::unnecessary_wraps)]
+const fn b(v: u8) -> Option<u8> {
+    Some(v)
+}
+
+const TYPE_DETAILS: &[TypeDetails] = &[
+    TypeDetails {
+        typ: FileType::Jpeg,
+        sigs: &[
+            &[b(0xFF), b(0xD8), b(0xFF), b(0xDB)],
+            &[
+                b(0xFF),
+                b(0xD8),
+                b(0xFF),
+                b(0xE0),
+                b(0x00),
+                b(0x10),
+                b(0x4A),
+                b(0x46),
+                b(0x49),
+                b(0x46),
+                b(0x00),
+                b(0x01),
+            ],
+            &[b(0xFF), b(0xD8), b(0xFF), b(0xEE)],
+            &[
+                b(0xFF),
+                b(0xD8),
+                b(0xFF),
+                b(0xE1),
+                None,
+                None,
+                b(0x45),
+                b(0x78),
+                b(0x69),
+                b(0x66),
+                b(0x00),
+                b(0x00),
+            ],
+            &[b(0xFF), b(0xD8), b(0xFF), b(0xE0)],
+        ],
+        exts: &[".jpg", ".jpeg", ".jfif"],
+    },
+    TypeDetails {
+        typ: FileType::Png,
+        sigs: &[&[
+            b(0x89),
+            b(0x50),
+            b(0x4E),
+            b(0x47),
+            b(0x0D),
+            b(0x0A),
+            b(0x1A),
+            b(0x0A),
+        ]],
+        exts: &[".png"],
+    },
+    TypeDetails {
+        typ: FileType::Gif,
+        sigs: &[
+            &[b(b'G'), b(b'I'), b(b'F'), b(b'8'), b(b'7'), b(b'a')],
+            &[b(b'G'), b(b'I'), b(b'F'), b(b'8'), b(b'9'), b(b'a')],
+        ],
+        exts: &[".gif"],
+    },
+    TypeDetails {
+        typ: FileType::Bmp,
+        sigs: &[&[b(b'B'), b(b'M')]],
+        exts: &[".bmp"],
+    },
+    TypeDetails {
+        typ: FileType::Qoi,
+        sigs: &[&[b(b'q'), b(b'o'), b(b'i'), b(b'f')]],
+        exts: &[".qoi"],
+    },
+    TypeDetails {
+        typ: FileType::Webp,
+        sigs: &[&[
+            b(0x52),
+            b(0x49),
+            b(0x46),
+            b(0x46),
+            None,
+            None,
+            None,
+            None,
+            b(0x57),
+            b(0x45),
+            b(0x42),
+            b(0x50),
+        ]],
+        exts: &[".webp"],
+    },
+];
+
+/// This is a helper for detecting file types based on magic bytes.
+///
+/// Ref: https://en.wikipedia.org/wiki/List_of_file_signatures
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FileType {
+    /// JPEG image file.
+    Jpeg,
+    /// PNG image file.
+    Png,
+    /// GIF image file.
+    Gif,
+    /// BMP image file.
+    Bmp,
+    /// QOI image file.
+    Qoi,
+    /// WebP image file.
+    Webp,
+    /// Unknown file format.
+    Unknown,
+}
+
+impl FileType {
+    /// Detect file type based on the magic bytes
+    /// at the start of the provided file contents.
+    pub fn detect(contents: &[u8]) -> FileType {
+        for typ in TYPE_DETAILS {
+            for signature in typ.sigs {
+                if contents.len() >= signature.len()
+                    && contents
+                        .iter()
+                        .zip(signature.iter())
+                        .all(|(f, sig)| sig.is_none_or(|s| *f == s))
+                {
+                    return typ.typ;
+                }
+            }
+        }
+        FileType::Unknown
+    }
+
+    /// Guess file type from its extension.
+    pub fn guess_from_extension(extension: &str) -> FileType {
+        for typ in TYPE_DETAILS {
+            for ext in typ.exts {
+                if extension.eq_ignore_ascii_case(ext) {
+                    return typ.typ;
+                }
+            }
+        }
+        FileType::Unknown
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // The Zig file has no tests; these cover the detection logic.
+    #[test]
+    fn detect_magic_bytes() {
+        assert_eq!(
+            FileType::detect(&[0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 1]),
+            FileType::Png
+        );
+        assert_eq!(FileType::detect(b"GIF89a...."), FileType::Gif);
+        assert_eq!(FileType::detect(b"BM"), FileType::Bmp);
+        assert_eq!(FileType::detect(b"qoif"), FileType::Qoi);
+        assert_eq!(
+            FileType::detect(b"RIFF\x01\x02\x03\x04WEBP"),
+            FileType::Webp
+        );
+        assert_eq!(
+            FileType::detect(b"RIFF\x01\x02\x03\x04WEBX"),
+            FileType::Unknown
+        );
+        assert_eq!(
+            FileType::detect(&[0xFF, 0xD8, 0xFF, 0xE1, 9, 9, 0x45, 0x78, 0x69, 0x66, 0, 0]),
+            FileType::Jpeg
+        );
+        assert_eq!(FileType::detect(&[0xFF, 0xD8, 0xFF, 0xE0]), FileType::Jpeg);
+        assert_eq!(FileType::detect(b""), FileType::Unknown);
+    }
+
+    #[test]
+    fn guess_from_extension_case_insensitive() {
+        assert_eq!(FileType::guess_from_extension(".JPG"), FileType::Jpeg);
+        assert_eq!(FileType::guess_from_extension(".jfif"), FileType::Jpeg);
+        assert_eq!(FileType::guess_from_extension(".webp"), FileType::Webp);
+        assert_eq!(FileType::guess_from_extension(".txt"), FileType::Unknown);
+    }
+}
diff --git a/crates/ghostty-os/src/flatpak.rs b/crates/ghostty-os/src/flatpak.rs
new file mode 100644
index 0000000..aab066c
--- /dev/null
+++ b/crates/ghostty-os/src/flatpak.rs
@@ -0,0 +1,400 @@
+use std::collections::HashMap;
+use std::os::fd::{AsFd, OwnedFd};
+use std::sync::{Arc, Condvar, Mutex};
+
+use zbus::blocking::{Connection, MessageIterator};
+use zbus::zvariant::Fd;
+use zbus::{MatchRule, message::Type as MessageType};
+
+const BUS_NAME: &str = "org.freedesktop.Flatpak";
+const OBJECT_PATH: &str = "/org/freedesktop/Flatpak/Development";
+const INTERFACE: &str = "org.freedesktop.Flatpak.Development";
+
+/// Returns true if we're running in a Flatpak environment.
+pub fn is_flatpak() -> bool {
+    std::path::Path::new("/.flatpak-info").exists()
+}
+
+/// Errors that are possible from us.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, thiserror::Error)]
+pub enum Error {
+    #[error("flatpak host command must be started")]
+    FlatpakMustBeStarted,
+    #[error("flatpak spawn failed")]
+    FlatpakSpawnFail,
+    #[error("flatpak setup failed")]
+    FlatpakSetupFail,
+    #[error("flatpak rpc failed")]
+    FlatpakRPCFail,
+}
+
+/// State the process is in.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum State {
+    /// Initial state
+    Init,
+    /// Error starting. The error message is only available via logs.
+    Err,
+    /// Process started with the given pid on the host.
+    Started { pid: u32 },
+    /// Process exited
+    Exited { pid: u32, status: u8 },
+}
+
+/// State shared with the dedicated thread, protected by the lock and
+/// condition variable.
+struct Shared {
+    state: Mutex<State>,
+    cv: Condvar,
+}
+
+impl Shared {
+    fn update(&self, state: State) {
+        let mut guard = self
+            .state
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        *guard = state;
+        self.cv.notify_all();
+    }
+}
+
+/// A struct to help execute commands on the host via the
+/// org.freedesktop.Flatpak.Development DBus module. This uses `zbus`
+/// (blocking API) rather than GIO/GLib.
+///
+/// This always spawns its own thread to wait for the exit signal. This makes
+/// it easy for the command to behave synchronously similar to
+/// `std::process::Child`.
+///
+/// There are lots of chances for low-hanging improvements here (automatic
+/// pipes, /dev/null, etc.) but this was purpose built for a specific need so
+/// it doesn't have all of those.
+///
+/// NOTE: this can't be exercised in the test environment (needs a Flatpak
+/// session bus with the Development interface); it is a best-effort port.
+pub struct FlatpakHostCommand {
+    /// Argv are the arguments to call on the host with argv[0] being
+    /// the command to execute.
+    pub argv: Vec<String>,
+
+    /// The cwd for the new process. If this is not set then it will use
+    /// the current cwd of the calling process.
+    pub cwd: Option<String>,
+
+    /// Environment variables for the child process. If this is None, this
+    /// does not send any environment variables.
+    pub env: Option<HashMap<String, String>>,
+
+    /// File descriptors to send to the child process. It is up to the
+    /// caller to create the file descriptors and set them up. They are
+    /// duplicated when spawning so the caller keeps ownership.
+    pub stdin: OwnedFd,
+    pub stdout: OwnedFd,
+    pub stderr: OwnedFd,
+
+    /// Connection kept for sending signals.
+    shared: Arc<Shared>,
+}
+
+impl FlatpakHostCommand {
+    pub fn new(argv: Vec<String>, stdin: OwnedFd, stdout: OwnedFd, stderr: OwnedFd) -> Self {
+        Self {
+            argv,
+            cwd: None,
+            env: None,
+            stdin,
+            stdout,
+            stderr,
+            shared: Arc::new(Shared {
+                state: Mutex::new(State::Init),
+                cv: Condvar::new(),
+            }),
+        }
+    }
+
+    fn state(&self) -> State {
+        *self
+            .shared
+            .state
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner)
+    }
+
+    /// Spawn the command. This will start the host command. On return,
+    /// the pid will be available. This must only be called with the
+    /// state in "init".
+    pub fn spawn(&mut self) -> Result<u32, Error> {
+        let request = Request {
+            argv: self.argv.clone(),
+            cwd: self.cwd.clone(),
+            env: self.env.clone().unwrap_or_default(),
+            fds: [
+                self.stdin
+                    .try_clone()
+                    .map_err(|_| Error::FlatpakSetupFail)?,
+                self.stdout
+                    .try_clone()
+                    .map_err(|_| Error::FlatpakSetupFail)?,
+                self.stderr
+                    .try_clone()
+                    .map_err(|_| Error::FlatpakSetupFail)?,
+            ],
+        };
+        let shared = Arc::clone(&self.shared);
+
+        // We don't track this thread, it will terminate on its own on
+        // command exit.
+        std::thread::Builder::new()
+            .name("flatpak-host-command".into())
+            .spawn(move || thread_main(&shared, request))
+            .map_err(|_| Error::FlatpakSpawnFail)?;
+
+        // Wait for the process to start or error.
+        let mut guard = self
+            .shared
+            .state
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        while *guard == State::Init {
+            guard = self
+                .shared
+                .cv
+                .wait(guard)
+                .unwrap_or_else(std::sync::PoisonError::into_inner);
+        }
+
+        match *guard {
+            State::Init => unreachable!(),
+            State::Err => Err(Error::FlatpakSpawnFail),
+            State::Started { pid } | State::Exited { pid, .. } => Ok(pid),
+        }
+    }
+
+    /// Wait for the process to end and return the exit status. This
+    /// can only be called ONCE. Once this returns, the state is reset.
+    pub fn wait(&mut self) -> Result<u8, Error> {
+        let mut guard = self
+            .shared
+            .state
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner);
+        loop {
+            match *guard {
+                State::Init => return Err(Error::FlatpakMustBeStarted),
+                State::Err => return Err(Error::FlatpakSpawnFail),
+                State::Started { .. } => {}
+                State::Exited { status, .. } => {
+                    *guard = State::Init;
+                    self.shared.cv.notify_all();
+                    return Ok(status);
+                }
+            }
+
+            guard = self
+                .shared
+                .cv
+                .wait(guard)
+                .unwrap_or_else(std::sync::PoisonError::into_inner);
+        }
+    }
+
+    /// Wait for the process to end asynchronously. The callback is invoked
+    /// from a helper thread with the result. This can only be called ONCE.
+    ///
+    /// This replaces `waitXev` (libxev completion) of the Zig version.
+    pub fn wait_callback(
+        mut self,
+        callback: impl FnOnce(Result<u8, Error>) + Send + 'static,
+    ) -> std::io::Result<()> {
+        std::thread::Builder::new()
+            .name("flatpak-host-wait".into())
+            .spawn(move || callback(self.wait()))?;
+        Ok(())
+    }
+
+    /// Send a signal to the started command. This does nothing if the
+    /// command is not in the started state.
+    pub fn signal(&self, sig: u8, pg: bool) -> Result<(), Error> {
+        let State::Started { pid } = self.state() else {
+            return Ok(());
+        };
+
+        // Get our bus connection.
+        let bus = Connection::session().map_err(|e| {
+            log::warn!("signal error getting bus: {e}");
+            Error::FlatpakSetupFail
+        })?;
+
+        if let Err(e) = bus.call_method(
+            Some(BUS_NAME),
+            OBJECT_PATH,
+            Some(INTERFACE),
+            "HostCommandSignal",
+            &(pid, u32::from(sig), pg),
+        ) {
+            log::warn!("signal send error: {e}");
+        }
+        Ok(())
+    }
+}
+
+struct Request {
+    argv: Vec<String>,
+    cwd: Option<String>,
+    env: HashMap<String, String>,
+    fds: [OwnedFd; 3],
+}
+
+fn thread_main(shared: &Shared, request: Request) {
+    // Get our bus connection. This has to remain active until we exit
+    // the thread otherwise our signals won't be called.
+    let bus = match Connection::session() {
+        Ok(b) => b,
+        Err(e) => {
+            log::warn!("spawn error getting bus: {e}");
+            shared.update(State::Err);
+            return;
+        }
+    };
+
+    // Spawn the command first. This will setup all our IO.
+    match start(shared, &bus, request) {
+        Ok(iter_and_pid) => {
+            let (iter, pid) = iter_and_pid;
+            wait_for_exit(shared, iter, pid);
+        }
+        Err(err) => {
+            log::warn!("error starting host command: {err}");
+            shared.update(State::Err);
+        }
+    }
+}
+
+/// Start the command. This will start the host command and set the
+/// pid on success. This will not wait for completion.
+fn start(
+    shared: &Shared,
+    bus: &Connection,
+    request: Request,
+) -> Result<(MessageIterator, u32), Error> {
+    // Build our file descriptor map: 0 -> stdin, 1 -> stdout, 2 -> stderr.
+    let mut fds: HashMap<u32, Fd<'_>> = HashMap::new();
+    for (i, fd) in request.fds.iter().enumerate() {
+        fds.insert(i as u32, Fd::from(fd.as_fd()));
+    }
+
+    // Build our args (arrays of NUL-terminated byte strings).
+    let args: Vec<Vec<u8>> = request
+        .argv
+        .iter()
+        .map(|a| {
+            let mut v = a.as_bytes().to_vec();
+            v.push(0);
+            v
+        })
+        .collect();
+
+    // Get the cwd in case we don't have ours set.
+    let cwd = match request.cwd {
+        Some(c) => c,
+        None => std::env::current_dir()
+            .map_err(|_| Error::FlatpakSetupFail)?
+            .to_string_lossy()
+            .into_owned(),
+    };
+    let mut cwd = cwd.into_bytes();
+    cwd.push(0);
+
+    // Subscribe to exit notifications (before the call so we can't miss it).
+    let rule = MatchRule::builder()
+        .msg_type(MessageType::Signal)
+        .sender(BUS_NAME)
+        .and_then(|b| b.interface(INTERFACE))
+        .and_then(|b| b.member("HostCommandExited"))
+        .and_then(|b| b.path(OBJECT_PATH))
+        .map(zbus::match_rule::Builder::build)
+        .map_err(|e| {
+            log::warn!("error building match rule: {e}");
+            Error::FlatpakSetupFail
+        })?;
+    let iter = MessageIterator::for_match_rule(rule, bus, None).map_err(|e| {
+        log::warn!("error subscribing to HostCommandExited: {e}");
+        Error::FlatpakSetupFail
+    })?;
+
+    // Go!
+    let reply = bus
+        .call_method(
+            Some(BUS_NAME),
+            OBJECT_PATH,
+            Some(INTERFACE),
+            "HostCommand",
+            &(cwd, args, fds, request.env, 0u32),
+        )
+        .map_err(|e| {
+            log::warn!("Flatpak.HostCommand failed: {e}");
+            Error::FlatpakRPCFail
+        })?;
+
+    let pid: u32 = reply.body().deserialize().map_err(|e| {
+        log::warn!("Flatpak.HostCommand bad reply: {e}");
+        Error::FlatpakRPCFail
+    })?;
+    log::debug!("HostCommand started pid={pid}");
+
+    shared.update(State::Started { pid });
+    Ok((iter, pid))
+}
+
+/// Block on the exit signal for our pid and publish the exit status.
+fn wait_for_exit(shared: &Shared, iter: MessageIterator, pid: u32) {
+    for msg in iter {
+        let Ok(msg) = msg else { continue };
+        let Ok((exit_pid, exit_status_raw)) = msg.body().deserialize::<(u32, u32)>() else {
+            continue;
+        };
+        if exit_pid != pid {
+            continue;
+        }
+
+        // posix.W.EXITSTATUS
+        let status = ((exit_status_raw >> 8) & 0xff) as u8;
+        shared.update(State::Exited { pid, status });
+        log::debug!("HostCommand exited pid={pid} status={status}");
+        return;
+    }
+
+    // The connection closed without an exit signal.
+    log::warn!("host command signal stream ended without exit pid={pid}");
+    shared.update(State::Err);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn is_flatpak_matches_flatpak_info() {
+        assert_eq!(
+            is_flatpak(),
+            std::path::Path::new("/.flatpak-info").exists()
+        );
+    }
+
+    #[test]
+    fn wait_before_spawn_errors() {
+        let (r, w) = crate::pipe::pipe().unwrap();
+        let w2 = w.try_clone().unwrap();
+        let mut cmd = FlatpakHostCommand::new(vec!["true".into()], r, w, w2);
+        assert_eq!(cmd.wait(), Err(Error::FlatpakMustBeStarted));
+        // Signalling an unstarted command is a no-op.
+        assert_eq!(cmd.signal(15, false), Ok(()));
+    }
+
+    #[test]
+    fn exit_status_extraction() {
+        // Mirrors posix.W.EXITSTATUS on a raw wait status.
+        assert_eq!(((3u32 << 8) >> 8) & 0xff, 3);
+    }
+}
diff --git a/crates/ghostty-os/src/homedir.rs b/crates/ghostty-os/src/homedir.rs
new file mode 100644
index 0000000..a0024b6
--- /dev/null
+++ b/crates/ghostty-os/src/homedir.rs
@@ -0,0 +1,152 @@
+use std::process::{Command, Stdio};
+
+use crate::passwd;
+
+#[derive(Debug, thiserror::Error, PartialEq, Eq)]
+pub enum Error {
+    /// The buffer used for output is not large enough to store the value.
+    #[error("buffer too small")]
+    BufferTooSmall,
+}
+
+#[derive(Debug, thiserror::Error, PartialEq, Eq)]
+pub enum ExpandError {
+    #[error("home detection failed")]
+    HomeDetectionFailed,
+    #[error("buffer too small")]
+    BufferTooSmall,
+}
+
+/// Equivalent of `std.fs.max_path_bytes` on Linux.
+const MAX_PATH_BYTES: usize = 4096;
+
+/// Determine the home directory for the currently executing user. This
+/// is generally an expensive process so the value should be cached.
+pub fn home() -> Result<Option<String>, Error> {
+    home_with_capacity(MAX_PATH_BYTES)
+}
+
+/// Like [`home`] but emulates the fixed output buffer of the Zig version:
+/// errors with `BufferTooSmall` if the result is longer than `cap` bytes.
+pub fn home_with_capacity(cap: usize) -> Result<Option<String>, Error> {
+    let check = |s: String| {
+        if cap < s.len() {
+            Err(Error::BufferTooSmall)
+        } else {
+            Ok(Some(s))
+        }
+    };
+
+    // First: if we have a HOME env var, then we use that.
+    if let Some(result) = std::env::var_os("HOME") {
+        return check(result.to_string_lossy().into_owned());
+    }
+
+    // We try passwd. This doesn't work on multi-user mac but we try it anyways.
+    if let Ok(pw) = passwd::get()
+        && let Some(result) = pw.home
+    {
+        return check(result);
+    }
+
+    // If all else fails, have the shell tell us...
+    let run = Command::new("/bin/sh")
+        .args(["-c", "cd && pwd"])
+        .stdin(Stdio::null())
+        .stderr(Stdio::null())
+        .output();
+    if let Ok(run) = run
+        && run.status.success()
+    {
+        let out = String::from_utf8_lossy(&run.stdout);
+        return check(trim_space(&out).to_owned());
+    }
+
+    Ok(None)
+}
+
+fn trim_space(input: &str) -> &str {
+    input.trim_matches([' ', '\n', '\t'])
+}
+
+/// Expands a path that starts with a tilde (~) to the home directory of
+/// the current user.
+///
+/// Errors if `home` fails or if the size of the expanded path is larger
+/// than the maximum path length.
+pub fn expand_home(path: &str) -> Result<String, ExpandError> {
+    expand_home_with_capacity(path, MAX_PATH_BYTES)
+}
+
+/// Like [`expand_home`] with an explicit output capacity (emulating the
+/// caller-provided buffer of the Zig version).
+pub fn expand_home_with_capacity(path: &str, cap: usize) -> Result<String, ExpandError> {
+    if !path.starts_with("~/") {
+        return Ok(path.to_owned());
+    }
+    let Ok(Some(home_dir)) = home_with_capacity(cap) else {
+        return Err(ExpandError::HomeDetectionFailed);
+    };
+    let rest = &path[1..]; // Skip the ~
+    let expanded_len = home_dir.len() + rest.len();
+
+    if expanded_len > cap {
+        return Err(ExpandError::BufferTooSmall);
+    }
+
+    Ok(format!("{home_dir}{rest}"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::testutil::with_env_lock;
+
+    #[test]
+    fn expand_home_unix() {
+        with_env_lock(|| {
+            let cap = MAX_PATH_BYTES;
+            let home_dir = expand_home_with_capacity("~/", cap).unwrap();
+            // Joining the home directory `~` with the path `/`
+            // the result should end with a separator here. (e.g. `/home/user/`)
+            assert!(home_dir.ends_with('/'));
+
+            let downloads = expand_home_with_capacity("~/Downloads/shader.glsl", cap).unwrap();
+            let expected_downloads = format!("{home_dir}Downloads/shader.glsl");
+            assert_eq!(expected_downloads, downloads);
+
+            assert_eq!("~", expand_home_with_capacity("~", cap).unwrap());
+            assert_eq!("~abc/", expand_home_with_capacity("~abc/", cap).unwrap());
+            assert_eq!(
+                "/home/user",
+                expand_home_with_capacity("/home/user", cap).unwrap()
+            );
+            assert_eq!("", expand_home_with_capacity("", cap).unwrap());
+
+            // Expect an error if the buffer is large enough to hold the home directory,
+            // but not the expanded path
+            assert_eq!(
+                Err(ExpandError::BufferTooSmall),
+                expand_home_with_capacity("~/Downloads", home_dir.len())
+            );
+        });
+    }
+
+    #[test]
+    fn home_is_detected() {
+        with_env_lock(|| {
+            let result = home().unwrap();
+            assert!(result.is_some());
+            assert!(!result.unwrap().is_empty());
+        });
+    }
+
+    #[test]
+    fn home_prefers_env() {
+        temp_env::with_var("HOME", Some("/some/home"), || {
+            assert_eq!(home().unwrap().as_deref(), Some("/some/home"));
+            assert_eq!(expand_home("~/x").unwrap(), "/some/home/x");
+            assert_eq!(home_with_capacity(3), Err(Error::BufferTooSmall));
+        });
+    }
+}
diff --git a/crates/ghostty-os/src/hostname.rs b/crates/ghostty-os/src/hostname.rs
new file mode 100644
index 0000000..9a7a37b
--- /dev/null
+++ b/crates/ghostty-os/src/hostname.rs
@@ -0,0 +1,158 @@
+#[derive(Debug, thiserror::Error, PartialEq, Eq)]
+pub enum LocalHostnameValidationError {
+    #[error("permission denied")]
+    PermissionDenied,
+    #[error("unexpected error")]
+    Unexpected,
+}
+
+/// Validates a hostname according to [RFC 1123](https://www.rfc-editor.org/rfc/rfc1123)
+///
+/// A permissive validator would consider strings like ".example.com",
+/// "exa..mple.com", and "-example.com" to be valid hostnames, which
+/// is incorrect.
+pub fn is_valid(hostname: &str) -> bool {
+    let hostname = hostname.as_bytes();
+    if hostname.is_empty() {
+        return false;
+    }
+    if hostname[0] == b'.' {
+        return false;
+    }
+
+    // Ignore trailing dot (FQDN). It doesn't count toward our length.
+    let end = if hostname[hostname.len() - 1] == b'.' {
+        if hostname.len() == 1 {
+            return false;
+        }
+        hostname.len() - 1
+    } else {
+        hostname.len()
+    };
+
+    if end > 253 {
+        return false;
+    }
+
+    // Hostnames are divided into dot-separated "labels", which:
+    //
+    // - Start with a letter or digit
+    // - Can contain letters, digits, or hyphens
+    // - Must end with a letter or digit
+    // - Have a minimum of 1 character and a maximum of 63
+    let mut label_start = 0usize;
+    let mut label_len = 0usize;
+    for (i, &c) in hostname[..end].iter().enumerate() {
+        match c {
+            b'.' => {
+                if label_len == 0 || label_len > 63 {
+                    return false;
+                }
+                if !hostname[label_start].is_ascii_alphanumeric() {
+                    return false;
+                }
+                if !hostname[i - 1].is_ascii_alphanumeric() {
+                    return false;
+                }
+
+                label_start = i + 1;
+                label_len = 0;
+            }
+            b'-' => {
+                label_len += 1;
+            }
+            _ => {
+                if !c.is_ascii_alphanumeric() {
+                    return false;
+                }
+                label_len += 1;
+            }
+        }
+    }
+
+    // Validate the final label
+    if label_len == 0 || label_len > 63 {
+        return false;
+    }
+    if !hostname[label_start].is_ascii_alphanumeric() {
+        return false;
+    }
+    if !hostname[end - 1].is_ascii_alphanumeric() {
+        return false;
+    }
+
+    true
+}
+
+/// The current machine's hostname (`gethostname`).
+fn our_hostname() -> String {
+    rustix::system::uname()
+        .nodename()
+        .to_string_lossy()
+        .into_owned()
+}
+
+/// Checks if a hostname is local to the current machine. This matches
+/// both "localhost" and the current hostname of the machine (as returned
+/// by `gethostname`).
+pub fn is_local(hostname: &str) -> Result<bool, LocalHostnameValidationError> {
+    // A 'localhost' hostname is always considered local.
+    if hostname == "localhost" {
+        return Ok(true);
+    }
+
+    // If hostname is not "localhost" it must match our hostname.
+    Ok(hostname == our_hostname())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn is_valid_hostnames() {
+        // Valid hostnames
+        assert!(is_valid("example"));
+        assert!(is_valid("example.com"));
+        assert!(is_valid("www.example.com"));
+        assert!(is_valid("sub.domain.example.com"));
+        assert!(is_valid("example.com."));
+        assert!(is_valid("host-name.example.com."));
+        assert!(is_valid("123.example.com."));
+        assert!(is_valid("a-b.com"));
+        assert!(is_valid("a.b.c.d.e.f.g"));
+        assert!(is_valid("127.0.0.1")); // Also a valid hostname
+        assert!(is_valid(&format!("{}.com", "a".repeat(63)))); // Label exactly 63 chars (valid)
+        assert!(is_valid(&format!("{}a", "a.".repeat(126)))); // Total length 253 (valid)
+
+        // Invalid hostnames
+        assert!(!is_valid(""));
+        assert!(!is_valid(".example.com"));
+        assert!(!is_valid("example.com.."));
+        assert!(!is_valid("host..domain"));
+        assert!(!is_valid("-hostname"));
+        assert!(!is_valid("hostname-"));
+        assert!(!is_valid("a.-.b"));
+        assert!(!is_valid("host_name.com"));
+        assert!(!is_valid("."));
+        assert!(!is_valid(".."));
+        assert!(!is_valid(&format!("{}.com", "a".repeat(64)))); // Label length 64 (too long)
+        assert!(!is_valid(&format!("{}ab", "a.".repeat(126)))); // Total length 254 (too long)
+    }
+
+    #[test]
+    fn is_local_returns_true_when_provided_hostname_is_localhost() {
+        assert!(is_local("localhost").unwrap());
+    }
+
+    #[test]
+    fn is_local_returns_true_when_hostname_is_local() {
+        let local = our_hostname();
+        assert!(is_local(&local).unwrap());
+    }
+
+    #[test]
+    fn is_local_returns_false_when_hostname_is_not_local() {
+        assert!(!is_local("not-the-local-hostname").unwrap());
+    }
+}
diff --git a/crates/ghostty-os/src/i18n.rs b/crates/ghostty-os/src/i18n.rs
new file mode 100644
index 0000000..5e499bd
--- /dev/null
+++ b/crates/ghostty-os/src/i18n.rs
@@ -0,0 +1,194 @@
+use std::path::Path;
+
+use crate::i18n_locales::LOCALES;
+
+/// Application bundle ID, used as the gettext domain
+/// (`build_config.bundle_id`).
+// TODO(integration): take from a shared build-config crate.
+pub const BUNDLE_ID: &str = "com.mitchellh.ghostty";
+
+/// Membership test for supported locales (Zig: `locales_map`).
+pub fn is_supported_locale(locale: &str) -> bool {
+    LOCALES.contains(&locale)
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum InitError {
+    #[error("invalid resources dir")]
+    InvalidResourcesDir,
+    #[error("out of memory")]
+    OutOfMemory,
+}
+
+/// Initialize i18n support for the application. This should be
+/// called automatically by the global state initialization.
+///
+/// This calls `bindtextdomain` for gettext with the proper directory
+/// of translations. This does NOT call `textdomain` as we don't
+/// want to set the domain for the entire application since this is also
+/// used by libghostty.
+pub fn init(resources_dir: &str) -> Result<(), InitError> {
+    // Our resources dir is always nested below the share dir that
+    // is standard for translations.
+    // (`std.fs.path.dirname` returns null for a bare relative name, where
+    // `Path::parent` returns an empty path.)
+    let share_dir = Path::new(resources_dir)
+        .parent()
+        .filter(|p| !p.as_os_str().is_empty())
+        .ok_or(InitError::InvalidResourcesDir)?;
+
+    // Build our locale path
+    let path = format!("{}/locale", share_dir.display());
+
+    // Bind our bundle ID to the given locale path
+    log::debug!("binding domain={BUNDLE_ID} path={path}");
+    gettextrs::bindtextdomain(BUNDLE_ID, path).map_err(|_| InitError::OutOfMemory)?;
+    Ok(())
+}
+
+/// Set the global gettext domain to our bundle ID, allowing unqualified
+/// `gettext` calls to look up translations for our application.
+///
+/// This should only be called for apprts that are fully owning the
+/// Ghostty application. This should not be called for libghostty users.
+pub fn init_global_domain() -> Result<(), InitError> {
+    gettextrs::textdomain(BUNDLE_ID).map_err(|_| InitError::OutOfMemory)?;
+    Ok(())
+}
+
+/// Translate a message for the Ghostty domain (Zig: `_`).
+pub fn tr(msgid: &str) -> String {
+    gettextrs::dgettext(BUNDLE_ID, msgid)
+}
+
+/// Canonicalize a locale name from a platform-specific value to
+/// a POSIX-compliant value.
+///
+/// The Zig version is a thin layer over gnulib's
+/// `_libintl_locale_name_canonicalize` (only linked when building libintl
+/// from source, i.e. macOS). That function isn't available here, so this is
+/// a pure-Rust approximation of the cases that matter: BCP-47 style tags
+/// have `-` replaced with `_` and the Chinese script tags are mapped to
+/// their POSIX region equivalents. Encodings are NOT parsed out (like the
+/// original, `en_US.UTF-8` becomes `en_US.UTF_8`).
+pub fn canonicalize_locale(locale: &str) -> String {
+    // Fix zh locales
+    if let Some(fixed) = fix_zh_locale(locale) {
+        return fixed.to_owned();
+    }
+
+    // Emulate gnulib's mapping of bare zh script tags.
+    match locale {
+        "zh-Hans" => return "zh_CN".to_owned(),
+        "zh-Hant" => return "zh_TW".to_owned(),
+        _ => {}
+    }
+
+    locale.replace('-', "_")
+}
+
+/// Handles some zh locales canonicalization because internal libintl
+/// canonicalization function doesn't handle correctly in these cases.
+fn fix_zh_locale(locale: &str) -> Option<&'static str> {
+    let mut it = locale.split('-');
+    let name = it.next()?;
+    if name != "zh" {
+        return None;
+    }
+
+    let script = it.next()?;
+    let region = it.next()?;
+
+    if script == "Hans" {
+        if region == "SG" {
+            return Some("zh_SG");
+        }
+        return Some("zh_CN");
+    }
+
+    if script == "Hant" {
+        if region == "MO" {
+            return Some("zh_MO");
+        }
+        if region == "HK" {
+            return Some("zh_HK");
+        }
+        return Some("zh_TW");
+    }
+
+    None
+}
+
+/// This can be called at any point a compile-time-known locale is
+/// available. In a `const` context this verifies the locale is supported
+/// (panics at compile time otherwise).
+pub const fn static_locale(v: &'static str) -> &'static str {
+    let vb = v.as_bytes();
+    let mut i = 0;
+    while i < LOCALES.len() {
+        let lb = LOCALES[i].as_bytes();
+        if lb.len() == vb.len() {
+            let mut j = 0;
+            let mut eq = true;
+            while j < lb.len() {
+                if lb[j] != vb[j] {
+                    eq = false;
+                    break;
+                }
+                j += 1;
+            }
+            if eq {
+                return LOCALES[i];
+            }
+        }
+        i += 1;
+    }
+    panic!("unsupported locale");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // The Zig test is darwin-only; the canonicalization here is portable.
+    #[test]
+    fn canonicalize_locale_darwin() {
+        assert_eq!("en_US", canonicalize_locale("en_US"));
+        assert_eq!("zh_CN", canonicalize_locale("zh-Hans"));
+        assert_eq!("zh_TW", canonicalize_locale("zh-Hant"));
+
+        assert_eq!("zh_CN", canonicalize_locale("zh-Hans-CN"));
+        assert_eq!("zh_SG", canonicalize_locale("zh-Hans-SG"));
+        assert_eq!("zh_TW", canonicalize_locale("zh-Hant-TW"));
+        assert_eq!("zh_HK", canonicalize_locale("zh-Hant-HK"));
+        assert_eq!("zh_MO", canonicalize_locale("zh-Hant-MO"));
+
+        // This is just an edge case I want to make sure we're aware of:
+        // canonicalizeLocale does not handle encodings and will turn them into
+        // underscores. We should parse them out before calling this function.
+        assert_eq!("en_US.UTF_8", canonicalize_locale("en_US.UTF-8"));
+    }
+
+    #[test]
+    fn locales_map_and_static_locale() {
+        assert!(is_supported_locale("zh_CN"));
+        assert!(is_supported_locale("kk"));
+        assert!(!is_supported_locale("xx"));
+        const L: &str = static_locale("de");
+        assert_eq!(L, "de");
+    }
+
+    #[test]
+    fn init_rejects_dirless_resources_dir() {
+        assert!(matches!(
+            init("ghostty"),
+            Err(InitError::InvalidResourcesDir)
+        ));
+        assert!(matches!(init("/"), Err(InitError::InvalidResourcesDir)));
+    }
+
+    #[test]
+    fn tr_falls_back_to_msgid() {
+        assert_eq!(tr("some untranslated message"), "some untranslated message");
+    }
+}
diff --git a/crates/ghostty-os/src/i18n_locales.rs b/crates/ghostty-os/src/i18n_locales.rs
new file mode 100644
index 0000000..7e24902
--- /dev/null
+++ b/crates/ghostty-os/src/i18n_locales.rs
@@ -0,0 +1,34 @@
+// NOTE: This is in a separate file because our build depends on it and
+// we want to minimize the transitive dependencies of the build binary
+// itself.
+
+/// Supported locales for the application. This must be kept up to date
+/// with the translations available in the `po/` directory; this is used
+/// by our build process as well runtime libghostty APIs.
+///
+/// The order also matters. For incomplete locale information (i.e. only
+/// a language code available), the first match is used. For example, if
+/// we know the user requested `zh` but has no script code, then we'd pick
+/// the first locale that matches `zh`.
+///
+/// For ordering, we prefer:
+///
+///   1. The most common locales first, since there are places in the code
+///      where we do linear searches for a locale and we want to minimize
+///      the number of iterations for the common case.
+///
+///   2. Alphabetical for otherwise equally common locales.
+///
+///   3. Most preferred locale for a language without a country code.
+///
+/// Note for "most common" locales, this is subjective and based on
+/// the perceived userbase of Ghostty, which may not be representative
+/// of general populations or global language distribution. Also note
+/// that ordering may be weird when we first merge a new locale since
+/// we don't have a good way to determine this. We can always reorder
+/// with some data.
+pub const LOCALES: [&str; 29] = [
+    "zh_CN", "de", "fr", "ja", "nl", "nb", "ru", "uk", "pl", "ko_KR", "mk", "tr", "id", "es_BO",
+    "es_AR", "es_ES", "pt_BR", "ca", "it", "bg", "ga", "hu", "he", "zh_TW", "hr", "lt", "lv", "vi",
+    "kk",
+];
diff --git a/crates/ghostty-os/src/kernel_info.rs b/crates/ghostty-os/src/kernel_info.rs
new file mode 100644
index 0000000..a907831
--- /dev/null
+++ b/crates/ghostty-os/src/kernel_info.rs
@@ -0,0 +1,29 @@
+use std::io::Read;
+
+/// Returns the kernel release string (`/proc/sys/kernel/osrelease`).
+pub fn get_kernel_info() -> Option<String> {
+    let file = std::fs::File::open("/proc/sys/kernel/osrelease").ok()?;
+
+    // 128 bytes should be enough to hold the kernel information. Zig's
+    // readToEndAlloc fails if the file is larger than the limit.
+    let mut buf = Vec::new();
+    file.take(129).read_to_end(&mut buf).ok()?;
+    if buf.len() > 128 {
+        return None;
+    }
+    let s = String::from_utf8_lossy(&buf);
+    Some(s.trim_matches(|c: char| c.is_ascii_whitespace()).to_owned())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn read_proc_sys_kernel_osrelease() {
+        let kernel_info = get_kernel_info().unwrap();
+        // Since we can't hardcode the info in tests, just check
+        // if something was read from the file
+        assert!(!kernel_info.is_empty());
+    }
+}
diff --git a/crates/ghostty-os/src/lib.rs b/crates/ghostty-os/src/lib.rs
index bcb1e4e..895c48d 100644
--- a/crates/ghostty-os/src/lib.rs
+++ b/crates/ghostty-os/src/lib.rs
@@ -1 +1,101 @@
-//! ghostty-os: see docs/rewrite/ARCHITECTURE.md for the module map.
+//! The "os" package contains utilities for interfacing with the operating
+//! system. These aren't restricted to syscalls or low-level operations, but
+//! also OS-specific features and conventions.
+//!
+//! Port of `src/os/*.zig` (Linux only) plus `src/file_type.zig`. See
+//! `docs/rewrite/notes/ghostty-os.md` for deviations and skipped files.
+
+#![cfg_attr(
+    test,
+    allow(
+        clippy::unwrap_used,
+        clippy::assert_is_empty,
+        clippy::items_after_statements
+    )
+)]
+
+pub mod args;
+pub mod cgroup;
+pub mod dbus;
+pub mod desktop;
+pub mod env;
+pub mod file;
+pub mod file_type;
+pub mod flatpak;
+pub mod homedir;
+pub mod hostname;
+pub mod i18n;
+pub mod i18n_locales;
+pub mod kernel_info;
+pub mod locale;
+pub mod mouse;
+pub mod open;
+pub mod passwd;
+pub mod path;
+pub mod pipe;
+pub mod resourcesdir;
+pub mod shell;
+pub mod string_encoding;
+pub mod systemd;
+pub mod temp_dir;
+pub mod uri;
+pub mod xdg;
+
+#[cfg(test)]
+pub(crate) mod testutil;
+
+// Functions and types (mirrors the flat exports of `os/main.zig`).
+pub use dbus::launched_by_dbus_activation;
+pub use desktop::{DesktopEnvironment, desktop_environment, launched_from_desktop};
+pub use env::{append_env, append_env_always, get_env_map, getenv, getenv_not_empty, prepend_env};
+pub use file::{Rlimit, alloc_tmp_dir, fix_max_files, restore_max_files};
+pub use flatpak::{FlatpakHostCommand, is_flatpak};
+pub use homedir::{expand_home, home};
+pub use kernel_info::get_kernel_info;
+pub use locale::ensure_locale;
+pub use mouse::click_interval;
+pub use open::open;
+pub use pipe::pipe;
+pub use resourcesdir::{ResourcesDir, resources_dir};
+pub use shell::ShellEscapeWriter;
+pub use systemd::launched_by_systemd;
+pub use temp_dir::TempDir;
+
+/// Join path components like `std.fs.path.join` (POSIX): empty components
+/// are skipped and exactly one separator is placed between components.
+pub(crate) fn path_join(parts: &[&str]) -> String {
+    let mut out = String::new();
+    for p in parts {
+        if p.is_empty() {
+            continue;
+        }
+        if out.is_empty() {
+            out.push_str(p);
+            continue;
+        }
+        let prev_sep = out.ends_with('/');
+        let this_sep = p.starts_with('/');
+        match (prev_sep, this_sep) {
+            (true, true) => out.push_str(&p[1..]),
+            (false, false) => {
+                out.push('/');
+                out.push_str(p);
+            }
+            _ => out.push_str(p),
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::path_join;
+
+    #[test]
+    fn path_join_basics() {
+        assert_eq!(path_join(&["/a", ".cache", ""]), "/a/.cache");
+        assert_eq!(path_join(&["/a/", "/b"]), "/a/b");
+        assert_eq!(path_join(&["", "b"]), "b");
+        assert_eq!(path_join(&["/a", "b", "c"]), "/a/b/c");
+    }
+}
diff --git a/crates/ghostty-os/src/locale.rs b/crates/ghostty-os/src/locale.rs
new file mode 100644
index 0000000..0324108
--- /dev/null
+++ b/crates/ghostty-os/src/locale.rs
@@ -0,0 +1,44 @@
+//! Locale setup (`os/locale.zig`).
+//!
+//! DEFERRED: the Zig `ensureLocale` is built from `setlocale(LC_ALL, "")`
+//! plus `setenv`/`unsetenv` of `LANG`. All of these are `unsafe` in Rust
+//! (`libc::setlocale`, `gettextrs::setlocale` and Rust 2024's
+//! `std::env::set_var`) and this crate forbids `unsafe`. There is no safe
+//! crate that wraps `setlocale`.
+//!
+//! Resolution options for integration:
+//!   * GTK (`gtk_init`, called by `gtk4::init()`) already calls
+//!     `setlocale(LC_ALL, "")` on Linux, so for the GTK apprt nothing else is
+//!     needed for gettext/Pango to pick up the locale.
+//!   * If an explicit call is needed (e.g. CLI actions without GTK), an
+//!     `unsafe`-permitted crate (apprt-gtk / the root binary) must perform the
+//!     libc call; [`FALLBACK_LOCALE`] documents the Zig fallback behaviour
+//!     (try `setlocale(LC_ALL, "")`, then with `LANG` unset, then
+//!     `en_US.UTF-8` and export `LANG=en_US.UTF-8`).
+//!
+//! The macOS-specific `LANG` population from Cocoa is not applicable.
+
+/// The locale Ghostty falls back to (and exports as `LANG`) when the
+/// environment's locale can't be set.
+pub const FALLBACK_LOCALE: &str = "en_US.UTF-8";
+
+/// Ensure that the locale is set.
+///
+/// DEFERRED (see module docs): this is currently a no-op that only logs.
+/// Returns `Some(value)` when `LANG` should be set to `value` for child
+/// processes; always `None` for now.
+pub fn ensure_locale() -> Option<String> {
+    log::debug!("ensure_locale: setlocale is not available from safe Rust; relying on the toolkit");
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ensure_locale_is_noop() {
+        assert_eq!(ensure_locale(), None);
+        assert_eq!(FALLBACK_LOCALE, "en_US.UTF-8");
+    }
+}
diff --git a/crates/ghostty-os/src/mouse.rs b/crates/ghostty-os/src/mouse.rs
new file mode 100644
index 0000000..43d01e0
--- /dev/null
+++ b/crates/ghostty-os/src/mouse.rs
@@ -0,0 +1,6 @@
+/// The system-configured double-click interval if its available.
+///
+/// Only macOS can report this; on Linux this is always `None`.
+pub fn click_interval() -> Option<u32> {
+    None
+}
diff --git a/crates/ghostty-os/src/open.rs b/crates/ghostty-os/src/open.rs
new file mode 100644
index 0000000..34d349a
--- /dev/null
+++ b/crates/ghostty-os/src/open.rs
@@ -0,0 +1,92 @@
+use std::io;
+use std::process::{Command, Stdio};
+
+/// Kind of URL being opened (`apprt.action.OpenUrl.Kind`). On Linux the
+/// kind is ignored by [`open`] (it only matters for macOS `open -t`).
+// TODO(integration): replace with the apprt action's OpenUrl kind once
+// ghostty-core defines it.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum OpenUrlKind {
+    Text,
+    Html,
+    #[default]
+    Unknown,
+}
+
+/// Open a URL in the default handling application (via `xdg-open`).
+///
+/// Any output on stderr is logged as a warning in the application logs.
+/// Output on stdout is ignored.
+///
+/// This function is purposely simple for the sake of providing
+/// some portable way to open URLs. If you are implementing an
+/// apprt for Ghostty, you should consider doing something special-cased
+/// for your platform.
+pub fn open(kind: OpenUrlKind, url: &str) -> io::Result<()> {
+    let _ = kind;
+    let mut cmd = Command::new("xdg-open");
+    cmd.arg(url);
+
+    // Pipe stdout/stderr so we can collect output from the command.
+    cmd.stdin(Stdio::null())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped());
+
+    // In the snap on Linux the launcher exports LD_LIBRARY_PATH pointing at
+    // the snap's bundled libraries. Leaking this into child process can
+    // can be problematic, so let's drop it from the env.
+    // TODO(integration): Zig does this only for `build_config.snap` builds;
+    // we do it when running inside a snap (`SNAP` is set).
+    if std::env::var_os("SNAP").is_some() {
+        cmd.env_remove("LD_LIBRARY_PATH");
+    }
+
+    // Spawn the process on our same thread so we can detect failure
+    // quickly.
+    let child = cmd.spawn()?;
+
+    // Create a thread that handles collecting output and reaping
+    // the process. This is done in a separate thread because SOME
+    // open implementations block and some do not. It's easier to just
+    // spawn a thread to handle this so that we never block.
+    std::thread::Builder::new()
+        .name("open-url".into())
+        .spawn(move || open_thread(child))?;
+    Ok(())
+}
+
+fn open_thread(child: std::process::Child) {
+    // 50 KiB is the default value used by std.process.Child.run and should
+    // be enough to get the output we care about.
+    const OUTPUT_MAX_SIZE: usize = 50 * 1024;
+
+    let output = match child.wait_with_output() {
+        Ok(o) => o,
+        Err(e) => {
+            log::warn!("error waiting for open command err={e}");
+            return;
+        }
+    };
+
+    // If we have any stderr output we log it. This makes it easier for
+    // users to debug why some open commands may not work as expected.
+    let stderr = &output.stderr[..output.stderr.len().min(OUTPUT_MAX_SIZE)];
+    if !stderr.is_empty() {
+        log::warn!("wait stderr={}", String::from_utf8_lossy(stderr));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn open_reports_spawn_failure_quickly() {
+        // With an empty PATH, xdg-open can't be found; Zig detects this
+        // synchronously and so do we.
+        temp_env::with_var("PATH", Some("/nonexistent-dir"), || {
+            let err = open(OpenUrlKind::Unknown, "https://example.com").unwrap_err();
+            assert_eq!(err.kind(), io::ErrorKind::NotFound);
+        });
+    }
+}
diff --git a/crates/ghostty-os/src/passwd.rs b/crates/ghostty-os/src/passwd.rs
new file mode 100644
index 0000000..21fb6d5
--- /dev/null
+++ b/crates/ghostty-os/src/passwd.rs
@@ -0,0 +1,58 @@
+use crate::flatpak::is_flatpak;
+
+/// Entry that is retrieved from the passwd API. This only contains the fields
+/// we care about.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct Entry {
+    pub shell: Option<String>,
+    pub home: Option<String>,
+    pub name: Option<String>,
+}
+
+/// Get the passwd entry for the currently executing user.
+pub fn get() -> std::io::Result<Entry> {
+    let uid = nix::unistd::getuid();
+    let user = match nix::unistd::User::from_uid(uid) {
+        Ok(Some(user)) => user,
+        Ok(None) => {
+            // Future: let's check if a better shell is available like zsh
+            log::warn!("no pw entry to detect default shell, will default to 'sh'");
+            return Ok(Entry::default());
+        }
+        Err(e) => {
+            log::warn!("error retrieving pw entry code={e}");
+            return Ok(Entry::default());
+        }
+    };
+
+    // TODO(integration): Zig shells out to the host via
+    // FlatpakHostCommand + a pty (`getent passwd <name>`) when running in
+    // Flatpak, because the sandbox passwd entry only has a correct username.
+    // That needs the `ghostty-termio` Pty; until then we use the sandbox
+    // entry and warn.
+    if is_flatpak() {
+        log::warn!(
+            "flatpak detected, but host passwd lookup is not implemented; \
+             using sandbox passwd entry"
+        );
+    }
+
+    Ok(Entry {
+        shell: Some(user.shell.to_string_lossy().into_owned()),
+        home: Some(user.dir.to_string_lossy().into_owned()),
+        name: Some(user.name),
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn get_entry() {
+        // We should be able to get an entry
+        let entry = get().unwrap();
+        assert!(entry.shell.is_some());
+        assert!(entry.home.is_some());
+    }
+}
diff --git a/crates/ghostty-os/src/path.rs b/crates/ghostty-os/src/path.rs
new file mode 100644
index 0000000..51c1826
--- /dev/null
+++ b/crates/ghostty-os/src/path.rs
@@ -0,0 +1,107 @@
+use std::io;
+use std::os::unix::fs::PermissionsExt;
+
+/// Equivalent of `std.fs.max_path_bytes` on Linux.
+const MAX_PATH_BYTES: usize = 4096;
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("path too long")]
+    PathTooLong,
+    #[error("access denied")]
+    AccessDenied,
+    #[error(transparent)]
+    Io(#[from] io::Error),
+}
+
+/// Search for "cmd" in the PATH and return the absolute path.
+pub fn expand(cmd: &str) -> Result<Option<String>, Error> {
+    // If the command already contains a slash, then we return it as-is
+    // because it is assumed to be absolute or relative.
+    if cmd.contains('/') {
+        return Ok(Some(cmd.to_owned()));
+    }
+
+    let Some(path_var) = std::env::var_os("PATH") else {
+        return Ok(None);
+    };
+    let path_var = path_var.to_string_lossy();
+
+    let mut seen_eacces = false;
+    for search_path in path_var.split(':').filter(|s| !s.is_empty()) {
+        // We need enough space in our path buffer to store this
+        let path_len = search_path.len() + cmd.len() + 1;
+        if MAX_PATH_BYTES < path_len {
+            return Err(Error::PathTooLong);
+        }
+
+        let full_path = format!("{search_path}/{cmd}");
+
+        // Stat it
+        let f = match std::fs::File::open(&full_path) {
+            Ok(f) => f,
+            Err(e) => match e.kind() {
+                io::ErrorKind::NotFound => continue,
+                io::ErrorKind::PermissionDenied => {
+                    // Accumulate this and return it later so we can try other
+                    // paths that we have access to.
+                    seen_eacces = true;
+                    continue;
+                }
+                _ => return Err(e.into()),
+            },
+        };
+        let meta = f.metadata()?;
+        if !meta.is_dir() && is_executable(meta.permissions().mode()) {
+            return Ok(Some(full_path));
+        }
+    }
+
+    if seen_eacces {
+        return Err(Error::AccessDenied);
+    }
+
+    Ok(None)
+}
+
+fn is_executable(mode: u32) -> bool {
+    mode & 0o0111 != 0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // `uname -n` is the *nix equivalent of `hostname.exe` on Windows
+    #[test]
+    fn expand_hostname() {
+        let path = crate::testutil::with_env_lock(|| expand("uname").unwrap().unwrap());
+        assert!(path.len() > "uname".len());
+    }
+
+    #[test]
+    fn expand_does_not_exist() {
+        let path =
+            crate::testutil::with_env_lock(|| expand("thisreallyprobablydoesntexist123").unwrap());
+        assert!(path.is_none());
+    }
+
+    #[test]
+    fn expand_slash() {
+        let path = expand("foo/env").unwrap().unwrap();
+        assert_eq!(path.len(), 7);
+    }
+
+    #[test]
+    fn expand_skips_non_executable_and_dirs() {
+        let dir = crate::TempDir::init().unwrap();
+        std::fs::write(dir.path().join("plain"), b"x").unwrap();
+        std::fs::create_dir(dir.path().join("adir")).unwrap();
+        let p = dir.path();
+        let p = p.to_str().unwrap();
+        temp_env::with_var("PATH", Some(p), || {
+            assert!(expand("plain").unwrap().is_none());
+            assert!(expand("adir").unwrap().is_none());
+        });
+    }
+}
diff --git a/crates/ghostty-os/src/pipe.rs b/crates/ghostty-os/src/pipe.rs
new file mode 100644
index 0000000..885220b
--- /dev/null
+++ b/crates/ghostty-os/src/pipe.rs
@@ -0,0 +1,28 @@
+use std::io;
+use std::os::fd::OwnedFd;
+
+/// pipe() for POSIX. Sets CLOEXEC on the file descriptors.
+/// Returns `(read, write)`.
+pub fn pipe() -> io::Result<(OwnedFd, OwnedFd)> {
+    rustix::pipe::pipe_with(rustix::pipe::PipeFlags::CLOEXEC).map_err(io::Error::from)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::{Read, Write};
+
+    #[test]
+    fn pipe_roundtrip_cloexec() {
+        let (r, w) = pipe().unwrap();
+        let flags = rustix::io::fcntl_getfd(&r).unwrap();
+        assert!(flags.contains(rustix::io::FdFlags::CLOEXEC));
+        let mut w = std::fs::File::from(w);
+        let mut r = std::fs::File::from(r);
+        w.write_all(b"hi").unwrap();
+        drop(w);
+        let mut s = String::new();
+        r.read_to_string(&mut s).unwrap();
+        assert_eq!(s, "hi");
+    }
+}
diff --git a/crates/ghostty-os/src/resourcesdir.rs b/crates/ghostty-os/src/resourcesdir.rs
new file mode 100644
index 0000000..cc0ae00
--- /dev/null
+++ b/crates/ghostty-os/src/resourcesdir.rs
@@ -0,0 +1,181 @@
+use std::io;
+use std::path::Path;
+
+use crate::path_join;
+
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct ResourcesDir {
+    /// Avoid accessing these directly, use the app() and host() methods instead.
+    pub app_path: Option<String>,
+    pub host_path: Option<String>,
+}
+
+impl ResourcesDir {
+    /// Get the directory to the bundled resources directory accessible
+    /// by the application.
+    pub fn app(&self) -> Option<&str> {
+        self.app_path.as_deref()
+    }
+
+    /// Get the directory to the bundled resources directory accessible
+    /// by the host environment (i.e. for sandboxed applications). The
+    /// returned directory might not be accessible from the application
+    /// itself.
+    ///
+    /// In non-sandboxed environment, this should be the same as app().
+    pub fn host(&self) -> Option<&str> {
+        self.host_path.as_deref().or(self.app_path.as_deref())
+    }
+}
+
+/// Sentinels we look for in the path to know we've found the resources
+/// directory (Linux).
+const SENTINELS: [&str; 2] = ["terminfo/g/ghostty", "terminfo/x/xterm-ghostty"];
+
+/// Gets the directory to the bundled resources directory, if it
+/// exists (not all platforms or packages have it).
+///
+/// Zig's `builtin.mode == .Debug` is mapped to `cfg!(debug_assertions)`.
+pub fn resources_dir() -> io::Result<ResourcesDir> {
+    let exe = std::env::current_exe().ok();
+    let env = std::env::var("GHOSTTY_RESOURCES_DIR").ok();
+    Ok(resources_dir_impl(
+        cfg!(debug_assertions),
+        exe.as_deref(),
+        env,
+    ))
+}
+
+fn resources_dir_impl(debug: bool, exe: Option<&Path>, env: Option<String>) -> ResourcesDir {
+    // Use the GHOSTTY_RESOURCES_DIR environment variable in release builds.
+    //
+    // In debug builds we try using terminfo detection first instead, since
+    // if debug Ghostty is launched by an older version of Ghostty, it
+    // would inherit the old, stale resources of older Ghostty instead of the
+    // freshly built ones under zig-out/share/ghostty.
+    if !debug && let Some(dir) = env.as_ref().filter(|d| !d.is_empty()) {
+        return ResourcesDir {
+            app_path: Some(dir.clone()),
+            host_path: None,
+        };
+    }
+
+    // Get the path to our running binary
+    let Some(mut exe) = exe else {
+        return ResourcesDir::default();
+    };
+
+    // We have an exe path! Climb the tree looking for the terminfo
+    // bundle as we expect it.
+    while let Some(dir) = exe.parent() {
+        exe = dir;
+        let dir_str = dir.to_string_lossy();
+
+        // We look for a /usr/share style path.
+        for sentinel in SENTINELS {
+            if let Some(v) = maybe_dir(&dir_str, "share", sentinel) {
+                return ResourcesDir {
+                    app_path: Some(path_join(&[&v, "ghostty"])),
+                    host_path: None,
+                };
+            }
+        }
+    }
+
+    // If terminfo detection failed in debug builds (somehow),
+    // fallback and use the provided resources dir.
+    if debug && let Some(dir) = env.filter(|d| !d.is_empty()) {
+        return ResourcesDir {
+            app_path: Some(dir),
+            host_path: None,
+        };
+    }
+
+    ResourcesDir::default()
+}
+
+/// Little helper to check if the "base/sub/suffix" directory exists and
+/// if so return "base/sub". The "suffix" is just used as a way to verify a
+/// directory seems roughly right.
+pub fn maybe_dir(base: &str, sub: &str, suffix: &str) -> Option<String> {
+    let path = format!("{base}/{sub}/{suffix}");
+
+    // Folder doesn't exist. If a different error happens its okay
+    // we just ignore it and move on.
+    if Path::new(&path).exists() {
+        let len = path.len() - suffix.len() - 1;
+        return Some(path[..len].to_owned());
+    }
+
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn resources_dir_accessors() {
+        let mut r = ResourcesDir::default();
+        assert_eq!(r.app(), None);
+        assert_eq!(r.host(), None);
+        r.app_path = Some("/a".into());
+        assert_eq!(r.host(), Some("/a"));
+        r.host_path = Some("/h".into());
+        assert_eq!(r.app(), Some("/a"));
+        assert_eq!(r.host(), Some("/h"));
+    }
+
+    fn make_tree() -> crate::TempDir {
+        let td = crate::TempDir::init().unwrap();
+        std::fs::create_dir_all(td.path().join("share/terminfo/x")).unwrap();
+        std::fs::write(td.path().join("share/terminfo/x/xterm-ghostty"), b"").unwrap();
+        std::fs::create_dir_all(td.path().join("bin")).unwrap();
+        td
+    }
+
+    #[test]
+    fn detects_share_dir_from_exe() {
+        let td = make_tree();
+        let exe = td.path().join("bin/ghostty");
+        let r = resources_dir_impl(true, Some(&exe), None);
+        let expected = format!("{}/share/ghostty", td.path().display());
+        assert_eq!(r.app(), Some(expected.as_str()));
+    }
+
+    #[test]
+    fn env_in_release_wins_and_in_debug_is_fallback() {
+        let td = make_tree();
+        let exe = td.path().join("bin/ghostty");
+        let env = Some("/env/res".to_owned());
+        assert_eq!(
+            resources_dir_impl(false, Some(&exe), env.clone()).app(),
+            Some("/env/res")
+        );
+        assert_ne!(
+            resources_dir_impl(true, Some(&exe), env.clone()).app(),
+            Some("/env/res")
+        );
+        // Debug fallback when detection fails.
+        assert_eq!(
+            resources_dir_impl(true, Some(Path::new("/nonexistent/bin/x")), env).app(),
+            Some("/env/res")
+        );
+        // Empty env is ignored.
+        assert_eq!(
+            resources_dir_impl(false, None, Some(String::new())).app(),
+            None
+        );
+    }
+
+    #[test]
+    fn maybe_dir_checks_suffix() {
+        let td = make_tree();
+        let base = td.path().to_string_lossy().into_owned();
+        assert_eq!(
+            maybe_dir(&base, "share", "terminfo/x/xterm-ghostty"),
+            Some(format!("{base}/share"))
+        );
+        assert_eq!(maybe_dir(&base, "share", "terminfo/g/ghostty"), None);
+    }
+}
diff --git a/crates/ghostty-os/src/shell.rs b/crates/ghostty-os/src/shell.rs
new file mode 100644
index 0000000..67ba462
--- /dev/null
+++ b/crates/ghostty-os/src/shell.rs
@@ -0,0 +1,155 @@
+use std::ffi::{CString, NulError};
+use std::io::{self, Write};
+
+/// Builder for constructing space-separated shell command strings.
+#[derive(Debug, Default, Clone)]
+pub struct ShellCommandBuilder {
+    buffer: String,
+}
+
+impl ShellCommandBuilder {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Append an argument to the command with automatic space separation.
+    /// Empty arguments are ignored.
+    pub fn append_arg(&mut self, arg: &str) {
+        if arg.is_empty() {
+            return;
+        }
+        if !self.buffer.is_empty() {
+            self.buffer.push(' ');
+        }
+        self.buffer.push_str(arg);
+    }
+
+    /// The command written so far.
+    pub fn written(&self) -> &str {
+        &self.buffer
+    }
+
+    /// Get the final null-terminated command string.
+    pub fn to_owned_slice(self) -> Result<CString, NulError> {
+        CString::new(self.buffer)
+    }
+}
+
+/// Writer that escapes characters that shells treat specially to reduce the
+/// risk of injection attacks or other such weirdness. Specifically excludes
+/// linefeeds so that they can be used to delineate lists of file paths.
+pub struct ShellEscapeWriter<W: Write> {
+    child: W,
+}
+
+impl<W: Write> ShellEscapeWriter<W> {
+    pub fn new(child: W) -> Self {
+        Self { child }
+    }
+
+    pub fn into_inner(self) -> W {
+        self.child
+    }
+}
+
+impl<W: Write> Write for ShellEscapeWriter<W> {
+    fn write(&mut self, data: &[u8]) -> io::Result<usize> {
+        for &byte in data {
+            match byte {
+                b'\\' | b'"' | b'\'' | b'$' | b'`' | b'*' | b'?' | b' ' | b'|' | b'(' | b')' => {
+                    self.child.write_all(&[b'\\', byte])?;
+                }
+                _ => self.child.write_all(&[byte])?,
+            }
+        }
+        Ok(data.len())
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.child.flush()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn shell_command_builder() {
+        // Empty command
+        let cmd = ShellCommandBuilder::new();
+        assert_eq!("", cmd.written());
+
+        // Single arg
+        let mut cmd = ShellCommandBuilder::new();
+        cmd.append_arg("bash");
+        assert_eq!("bash", cmd.written());
+
+        // Multiple args
+        let mut cmd = ShellCommandBuilder::new();
+        cmd.append_arg("bash");
+        cmd.append_arg("--posix");
+        cmd.append_arg("-l");
+        assert_eq!("bash --posix -l", cmd.written());
+
+        // Empty arg
+        let mut cmd = ShellCommandBuilder::new();
+        cmd.append_arg("bash");
+        cmd.append_arg("");
+        assert_eq!("bash", cmd.written());
+
+        // toOwnedSlice
+        let mut cmd = ShellCommandBuilder::new();
+        cmd.append_arg("bash");
+        cmd.append_arg("--posix");
+        let result = cmd.to_owned_slice().unwrap();
+        assert_eq!(result.to_str().unwrap(), "bash --posix");
+        assert_eq!(result.as_bytes_with_nul().last(), Some(&0));
+    }
+
+    fn escape(input: &str) -> String {
+        let mut shell = ShellEscapeWriter::new(Vec::new());
+        shell.write_all(input.as_bytes()).unwrap();
+        String::from_utf8(shell.into_inner()).unwrap()
+    }
+
+    #[test]
+    fn shell_escape_1() {
+        assert_eq!(escape("abc"), "abc");
+    }
+
+    #[test]
+    fn shell_escape_2() {
+        assert_eq!(escape("a c"), "a\\ c");
+    }
+
+    #[test]
+    fn shell_escape_3() {
+        assert_eq!(escape("a?c"), "a\\?c");
+    }
+
+    #[test]
+    fn shell_escape_4() {
+        assert_eq!(escape("a\\c"), "a\\\\c");
+    }
+
+    #[test]
+    fn shell_escape_5() {
+        assert_eq!(escape("a|c"), "a\\|c");
+    }
+
+    #[test]
+    fn shell_escape_6() {
+        assert_eq!(escape("a\"c"), "a\\\"c");
+    }
+
+    #[test]
+    fn shell_escape_7() {
+        assert_eq!(escape("a(1)"), "a\\(1\\)");
+    }
+
+    #[test]
+    fn shell_escape_keeps_newlines() {
+        assert_eq!(escape("a\nb"), "a\nb");
+    }
+}
diff --git a/crates/ghostty-os/src/string_encoding.rs b/crates/ghostty-os/src/string_encoding.rs
new file mode 100644
index 0000000..144218b
--- /dev/null
+++ b/crates/ghostty-os/src/string_encoding.rs
@@ -0,0 +1,245 @@
+use std::io::{self, Write};
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("decode error")]
+    DecodeError,
+    #[error(transparent)]
+    Io(#[from] io::Error),
+}
+
+impl PartialEq for Error {
+    fn eq(&self, other: &Self) -> bool {
+        matches!((self, other), (Error::DecodeError, Error::DecodeError))
+    }
+}
+
+/// Decode date from the buffer that has been encoded in the same way that
+/// `bash`'s `printf %q` encodes a string and write it to the writer. If an
+/// error is returned garbage may have been written to the buffer.
+pub fn printf_q_decode<W: Write>(writer: &mut W, buf: &[u8]) -> Result<(), Error> {
+    let data: &[u8] = if buf.starts_with(b"$'") {
+        // Strip off `$''` quoting.
+        if buf.len() < 3 || !buf.ends_with(b"'") {
+            return Err(Error::DecodeError);
+        }
+        &buf[2..buf.len() - 1]
+    } else if buf.starts_with(b"'") {
+        // Strip off `''` quoting.
+        if buf.len() < 2 || !buf.ends_with(b"'") {
+            return Err(Error::DecodeError);
+        }
+        &buf[1..buf.len() - 1]
+    } else {
+        buf
+    };
+
+    let mut src = 0;
+    while src < data.len() {
+        match data[src] {
+            b'\\' => {
+                if src + 1 >= data.len() {
+                    return Err(Error::DecodeError);
+                }
+                let out = match data[src + 1] {
+                    c @ (b' ' | b'\\' | b'"' | b'\'' | b'$') => c,
+                    b'e' => 0x1b,
+                    b'n' => b'\n',
+                    b'r' => b'\r',
+                    b't' => b'\t',
+                    b'v' => 0x0b,
+                    _ => return Err(Error::DecodeError),
+                };
+                writer.write_all(&[out])?;
+                src += 2;
+            }
+            c => {
+                writer.write_all(&[c])?;
+                src += 1;
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Decode data from the buffer that has been URL percent encoded and write
+/// it to the given buffer. If an error is returned the garbage may have been
+/// written to the writer.
+pub fn url_percent_decode<W: Write>(writer: &mut W, buf: &[u8]) -> Result<(), Error> {
+    let mut src = 0;
+    while src < buf.len() {
+        match buf[src] {
+            b'%' => {
+                if src + 2 >= buf.len() {
+                    return Err(Error::DecodeError);
+                }
+                let (Some(hi), Some(lo)) = (hex(buf[src + 1]), hex(buf[src + 2])) else {
+                    return Err(Error::DecodeError);
+                };
+                writer.write_all(&[(hi << 4) | lo])?;
+                src += 3;
+            }
+            c => {
+                writer.write_all(&[c])?;
+                src += 1;
+            }
+        }
+    }
+    Ok(())
+}
+
+fn hex(c: u8) -> Option<u8> {
+    match c {
+        b'0'..=b'9' => Some(c - b'0'),
+        b'a'..=b'f' => Some(c - b'a' + 10),
+        b'A'..=b'F' => Some(c - b'A' + 10),
+        _ => None,
+    }
+}
+
+/// Is the given character valid in URI percent encoding?
+fn is_valid_char(c: u8) -> bool {
+    match c {
+        b' ' | b';' | b'=' => false,
+        _ => (0x20..=0x7e).contains(&c),
+    }
+}
+
+/// Write data to the writer after URI percent encoding.
+pub fn url_percent_encode<W: Write>(writer: &mut W, data: &[u8]) -> io::Result<()> {
+    for &c in data {
+        if is_valid_char(c) {
+            writer.write_all(&[c])?;
+        } else {
+            write!(writer, "%{c:02X}")?;
+        }
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn pq(s: &[u8]) -> Result<Vec<u8>, Error> {
+        let mut w = Vec::new();
+        printf_q_decode(&mut w, s).map(|()| w)
+    }
+
+    fn pd(s: &[u8]) -> Result<Vec<u8>, Error> {
+        let mut w = Vec::new();
+        url_percent_decode(&mut w, s).map(|()| w)
+    }
+
+    #[test]
+    fn printf_q_1() {
+        assert_eq!(pq(b"bobr\\ kurwa").unwrap(), b"bobr kurwa");
+    }
+
+    #[test]
+    fn printf_q_2() {
+        assert_eq!(pq(b"bobr\\nkurwa").unwrap(), b"bobr\nkurwa");
+    }
+
+    #[test]
+    fn printf_q_3() {
+        assert_eq!(pq(b"bobr\\dkurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_4() {
+        assert_eq!(pq(b"bobr kurwa\\"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_5() {
+        assert_eq!(pq(b"$'bobr kurwa'").unwrap(), b"bobr kurwa");
+    }
+
+    #[test]
+    fn printf_q_6() {
+        assert_eq!(pq(b"'bobr kurwa'").unwrap(), b"bobr kurwa");
+    }
+
+    #[test]
+    fn printf_q_7() {
+        assert_eq!(pq(b"$'bobr kurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_8() {
+        assert_eq!(pq(b"$'"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_9() {
+        assert_eq!(pq(b"'bobr kurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_10() {
+        assert_eq!(pq(b"'"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn printf_q_escapes() {
+        assert_eq!(
+            pq(b"\\e\\r\\t\\v\\\\\\\"\\'\\$").unwrap(),
+            b"\x1b\r\t\x0b\\\"'$"
+        );
+    }
+
+    #[test]
+    fn singles_percent() {
+        for c in 0..255u32 {
+            let lower = format!("%{c:02x}");
+            let decoded = pd(lower.as_bytes()).unwrap();
+            assert_eq!(decoded, [c as u8]);
+            let upper = format!("%{c:02X}");
+            let decoded = pd(upper.as_bytes()).unwrap();
+            assert_eq!(decoded, [c as u8]);
+        }
+    }
+
+    #[test]
+    fn percent_1() {
+        assert_eq!(pd(b"bobr%20kurwa").unwrap(), b"bobr kurwa");
+    }
+
+    #[test]
+    fn percent_2() {
+        assert_eq!(pd(b"bobr%2kurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn percent_3() {
+        assert_eq!(pd(b"bobr%kurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn percent_4() {
+        assert_eq!(pd(b"bobr%%kurwa"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn percent_5() {
+        assert_eq!(pd(b"bobr%20kurwa%20").unwrap(), b"bobr kurwa ");
+    }
+
+    #[test]
+    fn percent_6() {
+        assert_eq!(pd(b"bobr%20kurwa%2"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn percent_7() {
+        assert_eq!(pd(b"bobr%20kurwa%"), Err(Error::DecodeError));
+    }
+
+    #[test]
+    fn percent_encode() {
+        let mut w = Vec::new();
+        url_percent_encode(&mut w, b"a b;c=d\n\xc3\xa9~").unwrap();
+        assert_eq!(String::from_utf8(w).unwrap(), "a%20b%3Bc%3Dd%0A%C3%A9~");
+    }
+}
diff --git a/crates/ghostty-os/src/systemd.rs b/crates/ghostty-os/src/systemd.rs
new file mode 100644
index 0000000..8459ce9
--- /dev/null
+++ b/crates/ghostty-os/src/systemd.rs
@@ -0,0 +1,216 @@
+use std::io::Read;
+
+/// Kernel `TASK_COMM_LEN`.
+const TASK_COMM_LEN: u64 = 16;
+
+/// Returns true if the program was launched as a systemd service.
+///
+/// On Linux, this returns true if the program was launched as a systemd
+/// service. It will return false if Ghostty was launched any other way.
+pub fn launched_by_systemd() -> bool {
+    // On Linux, systemd sets the `INVOCATION_ID` (v232+) and the
+    // `JOURNAL_STREAM` (v231+) environment variables. If these
+    // environment variables are not present we were not launched by
+    // systemd.
+    if std::env::var_os("INVOCATION_ID").is_none() {
+        return false;
+    }
+    if std::env::var_os("JOURNAL_STREAM").is_none() {
+        return false;
+    }
+
+    // If `INVOCATION_ID` and `JOURNAL_STREAM` are present, check to make sure
+    // that our parent process is actually `systemd`, not some other terminal
+    // emulator that doesn't clean up those environment variables.
+    let ppid = rustix::process::getppid().map_or(0, rustix::process::Pid::as_raw_pid);
+    if ppid == 1 {
+        return true;
+    }
+
+    // If the parent PID is not 1 we need to check to see if we were launched by
+    // a user systemd daemon. Do that by checking the `/proc/<ppid>/comm`
+    // to see if it ends with `systemd`.
+    let comm_path = format!("/proc/{ppid}/comm");
+    let Ok(comm_file) = std::fs::File::open(&comm_path) else {
+        log::error!("unable to open '{comm_path}' for reading");
+        return false;
+    };
+
+    // The maximum length of the command name is defined by
+    // `TASK_COMM_LEN` in the Linux kernel. This is usually 16
+    // bytes at the time of writing (Jun 2025) so its set to that.
+    // Also, since we only care to compare to "systemd", anything
+    // longer can be assumed to not be systemd.
+    let mut comm_data = Vec::new();
+    if comm_file
+        .take(TASK_COMM_LEN)
+        .read_to_end(&mut comm_data)
+        .is_err()
+    {
+        log::error!("problems reading from '{comm_path}'");
+        return false;
+    }
+
+    let end = comm_data
+        .iter()
+        .rposition(|&b| b != b'\n')
+        .map_or(0, |i| i + 1);
+    &comm_data[..end] == b"systemd"
+}
+
+/// systemd notifications. Used by Ghostty to inform systemd of the state of the
+/// process. Currently only used to notify systemd that we are ready and that
+/// configuration reloading has started.
+///
+/// See: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
+///
+/// These functions are re-implemented (rather than using `libsystemd`) to
+/// avoid another external dependency. Linux systems that do not use
+/// `systemd` should never start Ghostty with the `NOTIFY_SOCKET` environment
+/// variable set and these functions essentially become a no-op.
+pub mod notify {
+    use rustix::net::{
+        AddressFamily, SendFlags, SocketAddrUnix, SocketFlags, SocketType, connect, send,
+        socket_with,
+    };
+
+    /// Send the given message to the UNIX socket specified in the NOTIFY_SOCKET
+    /// environment variable. If there NOTIFY_SOCKET environment variable does
+    /// not exist then no message is sent.
+    pub(super) fn send_message(message: &[u8]) {
+        // Get the socket address that should receive notifications.
+        let Some(socket_path) = std::env::var_os("NOTIFY_SOCKET") else {
+            return;
+        };
+        let socket_path = socket_path.as_encoded_bytes();
+
+        // If the socket address is an empty string return.
+        if socket_path.is_empty() {
+            return;
+        }
+
+        // The socket address must be a path or an abstract socket.
+        if socket_path[0] != b'/' && socket_path[0] != b'@' {
+            log::warn!(
+                "only AF_UNIX sockets with path or abstract namespace addresses are supported!"
+            );
+            return;
+        }
+
+        // sockaddr_un.path is 108 bytes.
+        if 108 < socket_path.len() {
+            log::warn!("NOTIFY_SOCKET path is too long!");
+            return;
+        }
+
+        // NOTE: the Zig version copies the path verbatim (including a
+        // leading '@'); the sd_notify protocol says a leading '@' denotes
+        // an abstract socket, which is what we do here.
+        let addr = if socket_path[0] == b'@' {
+            SocketAddrUnix::new_abstract_name(&socket_path[1..])
+        } else {
+            SocketAddrUnix::new(socket_path)
+        };
+        let addr = match addr {
+            Ok(addr) => addr,
+            Err(e) => {
+                log::warn!("invalid NOTIFY_SOCKET address: {e}");
+                return;
+            }
+        };
+
+        let sock = match socket_with(
+            AddressFamily::UNIX,
+            SocketType::DGRAM,
+            SocketFlags::CLOEXEC,
+            None,
+        ) {
+            Ok(s) => s,
+            Err(e) => {
+                log::warn!("creating socket failed: {e}");
+                return;
+            }
+        };
+
+        if let Err(e) = connect(&sock, &addr) {
+            log::warn!("unable to connect to notify socket: {e}");
+            return;
+        }
+
+        match send(&sock, message, SendFlags::empty()) {
+            Ok(written) if written < message.len() => {
+                log::warn!(
+                    "short write to notify socket: {written} < {}",
+                    message.len()
+                );
+            }
+            Ok(_) => {}
+            Err(e) => log::warn!("unable to write to notify socket: {e}"),
+        }
+    }
+
+    /// Tell systemd that we are ready or that we are finished reloading.
+    /// See: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#READY=1
+    pub fn ready() {
+        send_message(b"READY=1");
+    }
+
+    /// Tell systemd that we have started reloading our configuration.
+    /// See: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#RELOADING=1
+    /// and: https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#MONOTONIC_USEC=%E2%80%A6
+    pub fn reloading() {
+        let ts = rustix::time::clock_gettime(rustix::time::ClockId::Monotonic);
+        let now = ts.tv_sec * 1_000_000 + ts.tv_nsec / 1000;
+        let message = format!("RELOADING=1\nMONOTONIC_USEC={now}");
+        send_message(message.as_bytes());
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::os::unix::net::UnixDatagram;
+
+    #[test]
+    fn not_launched_without_env() {
+        temp_env::with_vars(
+            [("INVOCATION_ID", None::<&str>), ("JOURNAL_STREAM", None)],
+            || assert!(!launched_by_systemd()),
+        );
+        temp_env::with_vars(
+            [("INVOCATION_ID", Some("x")), ("JOURNAL_STREAM", None)],
+            || assert!(!launched_by_systemd()),
+        );
+    }
+
+    fn recv_with_socket(f: impl FnOnce()) -> String {
+        let dir = crate::TempDir::init().unwrap();
+        let path = dir.path().join("notify.sock");
+        let sock = UnixDatagram::bind(&path).unwrap();
+        sock.set_read_timeout(Some(std::time::Duration::from_secs(5)))
+            .unwrap();
+        temp_env::with_var("NOTIFY_SOCKET", Some(path.to_str().unwrap()), f);
+        let mut buf = [0u8; 128];
+        let n = sock.recv(&mut buf).unwrap();
+        String::from_utf8(buf[..n].to_vec()).unwrap()
+    }
+
+    #[test]
+    fn notify_ready_sends_message() {
+        assert_eq!(recv_with_socket(notify::ready), "READY=1");
+    }
+
+    #[test]
+    fn notify_reloading_sends_message() {
+        let msg = recv_with_socket(notify::reloading);
+        let rest = msg.strip_prefix("RELOADING=1\nMONOTONIC_USEC=").unwrap();
+        assert!(rest.parse::<i64>().unwrap() > 0);
+    }
+
+    #[test]
+    fn notify_without_socket_is_noop() {
+        temp_env::with_var("NOTIFY_SOCKET", None::<&str>, notify::ready);
+        temp_env::with_var("NOTIFY_SOCKET", Some(""), notify::ready);
+        temp_env::with_var("NOTIFY_SOCKET", Some("relative"), notify::ready);
+    }
+}
diff --git a/crates/ghostty-os/src/temp_dir.rs b/crates/ghostty-os/src/temp_dir.rs
new file mode 100644
index 0000000..2072ba3
--- /dev/null
+++ b/crates/ghostty-os/src/temp_dir.rs
@@ -0,0 +1,131 @@
+//! Creates a temporary directory at runtime that can be safely used to
+//! store temporary data and is destroyed on drop.
+
+use std::io;
+use std::os::unix::fs::DirBuilderExt;
+use std::path::{Path, PathBuf};
+
+use crate::file::alloc_tmp_dir;
+
+// The amount of random bytes to get to determine our filename.
+const RANDOM_BYTES: usize = 16;
+
+// Base64 alphabet, replacing the standard `+/` with `-_` so that it can
+// be used in a file name on any filesystem.
+const B64_ALPHABET: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+/// Unpadded base64 using [`B64_ALPHABET`].
+fn b64_encode(data: &[u8]) -> String {
+    let mut out = String::with_capacity((data.len() * 4).div_ceil(3));
+    for chunk in data.chunks(3) {
+        let n = match chunk.len() {
+            3 => u32::from(chunk[0]) << 16 | u32::from(chunk[1]) << 8 | u32::from(chunk[2]),
+            2 => u32::from(chunk[0]) << 16 | u32::from(chunk[1]) << 8,
+            _ => u32::from(chunk[0]) << 16,
+        };
+        let chars = chunk.len() + 1;
+        for i in 0..chars {
+            let idx = (n >> (18 - 6 * i)) & 0x3f;
+            out.push(B64_ALPHABET[idx as usize] as char);
+        }
+    }
+    out
+}
+
+#[derive(Debug)]
+pub struct TempDir {
+    /// Parent directory
+    parent: PathBuf,
+
+    /// Name of the directory (basename only).
+    name: String,
+}
+
+impl TempDir {
+    /// Create the temporary directory.
+    pub fn init() -> io::Result<TempDir> {
+        let parent = match alloc_tmp_dir() {
+            Some(p) => PathBuf::from(p),
+            None => std::env::current_dir()?,
+        };
+        // Verify the parent can be opened (Zig opens it as a Dir).
+        std::fs::read_dir(&parent)?;
+
+        // We now loop forever until we can find a directory that we can create.
+        loop {
+            let mut rand_buf = [0u8; RANDOM_BYTES];
+            rustix::rand::getrandom(&mut rand_buf, rustix::rand::GetRandomFlags::empty())?;
+            let name = b64_encode(&rand_buf);
+
+            match std::fs::DirBuilder::new()
+                .mode(0o755)
+                .create(parent.join(&name))
+            {
+                Ok(()) => return Ok(TempDir { parent, name }),
+                Err(e) if e.kind() == io::ErrorKind::AlreadyExists => {}
+                Err(e) => return Err(e),
+            }
+        }
+    }
+
+    /// Name returns the name of the directory. This is just the basename
+    /// and is not the full absolute path.
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// The parent directory containing the temporary directory.
+    pub fn parent(&self) -> &Path {
+        &self.parent
+    }
+
+    /// Full path to the temporary directory.
+    pub fn path(&self) -> PathBuf {
+        self.parent.join(&self.name)
+    }
+
+    /// Finish with the temporary directory. This deletes all contents in the
+    /// directory.
+    pub fn deinit(self) {}
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        if let Err(err) = std::fs::remove_dir_all(self.path()) {
+            log::error!("error deleting temp dir err={err}");
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn temp_dir_lifecycle() {
+        let td = TempDir::init().unwrap();
+        let name = td.name().to_owned();
+        assert!(!name.is_empty());
+        assert_eq!(name.len(), 22);
+
+        // Can open a new handle to it proves it exists.
+        let parent = td.parent().to_owned();
+        assert!(std::fs::read_dir(parent.join(&name)).is_ok());
+        std::fs::write(td.path().join("file"), b"x").unwrap();
+
+        // Should be deleted after we deinit
+        td.deinit();
+        let err = std::fs::read_dir(parent.join(&name)).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::NotFound);
+    }
+
+    #[test]
+    fn b64_encoder() {
+        assert_eq!(b64_encode(b""), "");
+        assert_eq!(b64_encode(b"f"), "Zg");
+        assert_eq!(b64_encode(b"fo"), "Zm8");
+        assert_eq!(b64_encode(b"foo"), "Zm9v");
+        assert_eq!(b64_encode(&[0xfb, 0xff]), "-_8");
+        assert_eq!(b64_encode(&[0u8; 16]).len(), 22);
+    }
+}
diff --git a/crates/ghostty-os/src/testutil.rs b/crates/ghostty-os/src/testutil.rs
new file mode 100644
index 0000000..33619ea
--- /dev/null
+++ b/crates/ghostty-os/src/testutil.rs
@@ -0,0 +1,9 @@
+//! Test helpers. Process environment mutation is `unsafe` in Rust 2024, so
+//! tests go through `temp_env`, which serializes env access with a global
+//! lock. Tests that merely *read* env vars that other tests mutate should
+//! take the same lock via [`with_env_lock`].
+
+/// Run `f` while holding the global env lock (no variables changed).
+pub fn with_env_lock<R>(f: impl FnOnce() -> R) -> R {
+    temp_env::with_vars(Vec::<(&str, Option<&str>)>::new(), f)
+}
diff --git a/crates/ghostty-os/src/uri.rs b/crates/ghostty-os/src/uri.rs
new file mode 100644
index 0000000..b3daf4a
--- /dev/null
+++ b/crates/ghostty-os/src/uri.rs
@@ -0,0 +1,506 @@
+//! URI parsing. Extends a faithful port of Zig's `std.Uri.parse` with the
+//! additional [`ParseOptions`] from `os/uri.zig`.
+
+use std::borrow::Cow;
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct ParseOptions {
+    /// Parse MAC addresses in the host component.
+    ///
+    /// This is useful when the "Private Wi-Fi address" is enabled on macOS,
+    /// which sets the hostname to a rotating MAC address (12:34:56:ab:cd:ef).
+    pub mac_address: bool,
+
+    /// Return the full, raw, unencoded path string. Any query and fragment
+    /// values will be return as part of the path instead of as distinct
+    /// fields.
+    pub raw_path: bool,
+}
+
+/// Errors of `std.Uri.ParseError` plus `InvalidMacAddress`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, thiserror::Error)]
+pub enum ParseError {
+    #[error("unexpected character")]
+    UnexpectedCharacter,
+    #[error("invalid format")]
+    InvalidFormat,
+    #[error("invalid port")]
+    InvalidPort,
+    #[error("invalid mac address")]
+    InvalidMacAddress,
+}
+
+/// `std.Uri.Component`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Component<'a> {
+    /// Unencoded text.
+    Raw(Cow<'a, str>),
+    /// Percent-encoded text.
+    PercentEncoded(&'a str),
+}
+
+impl Component<'_> {
+    pub fn is_empty(&self) -> bool {
+        match self {
+            Component::Raw(s) => s.is_empty(),
+            Component::PercentEncoded(s) => s.is_empty(),
+        }
+    }
+
+    /// The raw (percent-decoded) value (`toRaw`). Invalid escapes are left
+    /// as-is, matching `std.Uri.percentDecodeInPlace`.
+    pub fn to_raw(&self) -> Cow<'_, str> {
+        match self {
+            Component::Raw(s) => Cow::Borrowed(s.as_ref()),
+            Component::PercentEncoded(s) => percent_decode(s),
+        }
+    }
+
+    /// The percent-encoded value as it appears in the source, or the raw
+    /// text for `Raw` components.
+    pub fn as_str(&self) -> &str {
+        match self {
+            Component::Raw(s) => s,
+            Component::PercentEncoded(s) => s,
+        }
+    }
+}
+
+/// Lenient percent decoding like `std.Uri.percentDecodeBackwards`/InPlace:
+/// valid `%XX` sequences are decoded, everything else passes through.
+fn percent_decode(s: &str) -> Cow<'_, str> {
+    if !s.contains('%') {
+        return Cow::Borrowed(s);
+    }
+    let b = s.as_bytes();
+    let mut out = Vec::with_capacity(b.len());
+    let mut i = 0;
+    while i < b.len() {
+        if b[i] == b'%'
+            && i + 2 < b.len()
+            && let (Some(h), Some(l)) = (hexval(b[i + 1]), hexval(b[i + 2]))
+        {
+            out.push((h << 4) | l);
+            i += 3;
+            continue;
+        }
+        out.push(b[i]);
+        i += 1;
+    }
+    Cow::Owned(String::from_utf8_lossy(&out).into_owned())
+}
+
+fn hexval(c: u8) -> Option<u8> {
+    match c {
+        b'0'..=b'9' => Some(c - b'0'),
+        b'a'..=b'f' => Some(c - b'a' + 10),
+        b'A'..=b'F' => Some(c - b'A' + 10),
+        _ => None,
+    }
+}
+
+/// `std.Uri`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Uri<'a> {
+    pub scheme: &'a str,
+    pub user: Option<Component<'a>>,
+    pub password: Option<Component<'a>>,
+    pub host: Option<Component<'a>>,
+    pub port: Option<u16>,
+    pub path: Component<'a>,
+    pub query: Option<Component<'a>>,
+    pub fragment: Option<Component<'a>>,
+}
+
+/// Port of `std.Uri.parse`.
+fn std_parse(text: &str) -> Result<Uri<'_>, ParseError> {
+    let Some(colon) = text.find(':') else {
+        return Err(ParseError::UnexpectedCharacter);
+    };
+    let scheme = &text[..colon];
+    parse_after_scheme(scheme, &text[colon + 1..])
+}
+
+/// Port of `std.Uri.parseAfterScheme`.
+fn parse_after_scheme<'a>(scheme: &'a str, text: &'a str) -> Result<Uri<'a>, ParseError> {
+    let mut uri = Uri {
+        scheme,
+        user: None,
+        password: None,
+        host: None,
+        port: None,
+        path: Component::PercentEncoded(""),
+        query: None,
+        fragment: None,
+    };
+    let mut rest = text;
+
+    if let Some(after) = rest.strip_prefix("//") {
+        // authority part
+        let end = after.find(['/', '?', '#']).unwrap_or(after.len());
+        let authority = &after[..end];
+        rest = &after[end..];
+
+        if authority.is_empty() {
+            if !rest.starts_with('/') {
+                return Err(ParseError::InvalidFormat);
+            }
+        } else {
+            parse_authority(authority, &mut uri)?;
+        }
+    }
+
+    let path_end = rest.find(['?', '#']).unwrap_or(rest.len());
+    uri.path = Component::PercentEncoded(&rest[..path_end]);
+    rest = &rest[path_end..];
+    if let Some(after) = rest.strip_prefix('?') {
+        // query part
+        let end = after.find('#').unwrap_or(after.len());
+        uri.query = Some(Component::PercentEncoded(&after[..end]));
+        rest = &after[end..];
+    }
+    if let Some(after) = rest.strip_prefix('#') {
+        uri.fragment = Some(Component::PercentEncoded(after));
+    }
+    Ok(uri)
+}
+
+fn parse_authority<'a>(authority: &'a str, uri: &mut Uri<'a>) -> Result<(), ParseError> {
+    let mut start_of_host = 0;
+    if let Some(index) = authority.find('@') {
+        start_of_host = index + 1;
+        let user_info = &authority[..index];
+
+        if let Some(idx) = user_info.find(':') {
+            uri.user = Some(Component::PercentEncoded(&user_info[..idx]));
+            if idx + 1 < user_info.len() {
+                // empty password is also "no password"
+                uri.password = Some(Component::PercentEncoded(&user_info[idx + 1..]));
+            }
+        } else {
+            uri.user = Some(Component::PercentEncoded(user_info));
+            uri.password = None;
+        }
+    }
+
+    // only possible if uri consists of only `userinfo@`
+    if start_of_host >= authority.len() {
+        return Ok(());
+    }
+
+    let mut end_of_host = authority.len();
+    let ab = authority.as_bytes();
+
+    // if we see `]` first without `@`
+    if ab[start_of_host] == b']' {
+        return Err(ParseError::InvalidFormat);
+    }
+
+    if ab[start_of_host] == b'[' {
+        // IPv6
+        end_of_host = authority.rfind(']').ok_or(ParseError::InvalidFormat)? + 1;
+
+        if let Some(index) = authority.rfind(':')
+            && index >= end_of_host
+        {
+            // if not part of the V6 address field
+            end_of_host = end_of_host.min(index);
+            uri.port = Some(
+                authority[index + 1..]
+                    .parse::<u16>()
+                    .map_err(|_| ParseError::InvalidPort)?,
+            );
+        }
+    } else if let Some(index) = authority.rfind(':')
+        && index >= start_of_host
+    {
+        // if not part of the userinfo field
+        end_of_host = end_of_host.min(index);
+        uri.port = Some(
+            authority[index + 1..]
+                .parse::<u16>()
+                .map_err(|_| ParseError::InvalidPort)?,
+        );
+    }
+
+    uri.host = Some(Component::PercentEncoded(
+        &authority[start_of_host..end_of_host],
+    ));
+    Ok(())
+}
+
+/// Byte offset of `inner` within `outer` (both must be sub-slices of the
+/// same allocation; here `inner` always comes from parsing `outer`).
+fn offset_in(outer: &str, inner: &str) -> usize {
+    inner.as_ptr() as usize - outer.as_ptr() as usize
+}
+
+/// Parses a URI from the given string.
+///
+/// This extends the standard URI parse with some additional ParseOptions.
+pub fn parse(text: &str, options: ParseOptions) -> Result<Uri<'_>, ParseError> {
+    let mut uri = match std_parse(text) {
+        Ok(uri) => uri,
+        Err(err) => {
+            // We can attempt to re-parse the text as a URI that has a MAC address
+            // in its host field (which tripped up the standard port parsing):
+            //
+            //      file://12:34:56:78:90:aa/path/to/file
+            //                            ^^ InvalidPort
+            //
+            if err != ParseError::InvalidPort || !options.mac_address {
+                return Err(err);
+            }
+
+            // We can assume that the initial parse already validated the
+            // scheme, so we only need to find its bounds within the string.
+            let scheme_end = text.find("://").ok_or(ParseError::InvalidFormat)?;
+            let scheme = &text[..scheme_end];
+
+            // We similarly find the bounds of the host component by looking
+            // for the first slash (/) after the scheme. This is all we need
+            // for this case because the resulting slice can be unambiguously
+            // determined to be a MAC address (or not).
+            let host_start = scheme_end + "://".len();
+            let host_end = text[host_start..]
+                .find('/')
+                .map_or(text.len(), |i| host_start + i);
+            let mac_address = &text[host_start..host_end];
+            if !is_valid_mac_address(mac_address) {
+                return Err(ParseError::InvalidMacAddress);
+            }
+
+            // Parse the rest of the text (starting with the path component) as a
+            // partial URI and then add our MAC address as its host component.
+            let mut uri = parse_after_scheme(scheme, &text[host_end..])?;
+            uri.host = Some(Component::PercentEncoded(mac_address));
+            uri
+        }
+    };
+
+    // When MAC address parsing is enabled, we need to handle the case where
+    // the standard parse parsed the address's last octet as a numeric port number.
+    // We use a few heuristics to identify this case (14 characters, 4 colons)
+    // and then "repair" the result by reassign the .host component to the full
+    // MAC address and clearing the .port component.
+    //
+    //    12:34:56:78:90:99 -> [12:34:56:78:90, 99] -> 12:34:56:78:90:99
+    //    (original host)      (parsed host + port)    (restored host)
+    //
+    if options.mac_address
+        && let Some(Component::PercentEncoded(host)) = uri.host.clone()
+        && host.len() == 14
+        && host.matches(':').count() == 4
+        && let Some(port) = uri.port
+        && port <= 99
+    {
+        // The parse returns slices pointing into the original text string.
+        let host_start = offset_in(text, host);
+        let path_start = offset_in(text, uri.path.as_str());
+        let mac_address = &text[host_start..path_start];
+        if !is_valid_mac_address(mac_address) {
+            return Err(ParseError::InvalidMacAddress);
+        }
+
+        uri.host = Some(Component::PercentEncoded(mac_address));
+        uri.port = None;
+    }
+
+    // When the raw_path option is active, return everything after the authority
+    // (host) in the .path component, including any query and fragment values.
+    if options.raw_path {
+        let path_start = offset_in(text, uri.path.as_str());
+        uri.path = Component::Raw(Cow::Borrowed(&text[path_start..]));
+        uri.query = None;
+        uri.fragment = None;
+    }
+
+    Ok(uri)
+}
+
+/// Checks if a string represents a valid MAC address, e.g. 12:34:56:ab:cd:ef.
+fn is_valid_mac_address(s: &str) -> bool {
+    let b = s.as_bytes();
+    if b.len() != 17 {
+        return false;
+    }
+
+    for (i, &c) in b.iter().enumerate() {
+        if i % 3 == 2 {
+            if c != b':' {
+                return false;
+            }
+        } else if !c.is_ascii_hexdigit() {
+            return false;
+        }
+    }
+
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const MAC: ParseOptions = ParseOptions {
+        mac_address: true,
+        raw_path: false,
+    };
+
+    fn host<'a>(u: &'a Uri<'_>) -> &'a str {
+        match u.host.as_ref().unwrap() {
+            Component::PercentEncoded(s) => s,
+            Component::Raw(_) => panic!("raw host"),
+        }
+    }
+
+    #[test]
+    fn parse_mac_address() {
+        // Numeric MAC address without a port
+        let uri1 = parse("file://00:12:34:56:78:90/path", MAC).unwrap();
+        assert_eq!("file", uri1.scheme);
+        assert_eq!("00:12:34:56:78:90", host(&uri1));
+        assert_eq!("/path", uri1.path.as_str());
+        assert_eq!(None, uri1.port);
+
+        // Numeric MAC address with a port
+        let uri2 = parse("file://00:12:34:56:78:90:999/path", MAC).unwrap();
+        assert_eq!("file", uri2.scheme);
+        assert_eq!("00:12:34:56:78:90", host(&uri2));
+        assert_eq!("/path", uri2.path.as_str());
+        assert_eq!(Some(999), uri2.port);
+
+        // Alphabetic MAC address without a port
+        let uri3 = parse("file://ab:cd:ef:ab:cd:ef/path", MAC).unwrap();
+        assert_eq!("file", uri3.scheme);
+        assert_eq!("ab:cd:ef:ab:cd:ef", host(&uri3));
+        assert_eq!("/path", uri3.path.as_str());
+        assert_eq!(None, uri3.port);
+
+        // Alphabetic MAC address with a port
+        let uri4 = parse("file://ab:cd:ef:ab:cd:ef:999/path", MAC).unwrap();
+        assert_eq!("file", uri4.scheme);
+        assert_eq!("ab:cd:ef:ab:cd:ef", host(&uri4));
+        assert_eq!("/path", uri4.path.as_str());
+        assert_eq!(Some(999), uri4.port);
+
+        // Numeric MAC address without a path component
+        let uri5 = parse("file://00:12:34:56:78:90", MAC).unwrap();
+        assert_eq!("file", uri5.scheme);
+        assert_eq!("00:12:34:56:78:90", host(&uri5));
+        assert!(uri5.path.is_empty());
+
+        // Alphabetic MAC address without a path component
+        let uri6 = parse("file://ab:cd:ef:ab:cd:ef", MAC).unwrap();
+        assert_eq!("file", uri6.scheme);
+        assert_eq!("ab:cd:ef:ab:cd:ef", host(&uri6));
+        assert!(uri6.path.is_empty());
+
+        // Invalid MAC addresses
+        assert_eq!(
+            Err(ParseError::InvalidMacAddress),
+            parse("file://zz:zz:zz:zz:zz:00/path", MAC)
+        );
+        assert_eq!(
+            Err(ParseError::InvalidMacAddress),
+            parse("file://zz:zz:zz:zz:zz:zz/path", MAC)
+        );
+    }
+
+    #[test]
+    fn parse_raw_path() {
+        let text = "file://localhost/path??#fragment";
+
+        let uri1 = parse(
+            text,
+            ParseOptions {
+                raw_path: false,
+                ..Default::default()
+            },
+        )
+        .unwrap();
+        assert_eq!("file", uri1.scheme);
+        assert_eq!("localhost", host(&uri1));
+        assert_eq!("/path", uri1.path.to_raw());
+        assert_eq!("?", uri1.query.as_ref().unwrap().as_str());
+        assert_eq!("fragment", uri1.fragment.as_ref().unwrap().as_str());
+
+        let uri2 = parse(
+            text,
+            ParseOptions {
+                raw_path: true,
+                ..Default::default()
+            },
+        )
+        .unwrap();
+        assert_eq!("file", uri2.scheme);
+        assert_eq!("localhost", host(&uri2));
+        assert_eq!("/path??#fragment", uri2.path.to_raw());
+        assert_eq!(None, uri2.query);
+        assert_eq!(None, uri2.fragment);
+
+        let uri3 = parse(
+            "file://localhost",
+            ParseOptions {
+                raw_path: true,
+                ..Default::default()
+            },
+        )
+        .unwrap();
+        assert_eq!("file", uri3.scheme);
+        assert_eq!("localhost", host(&uri3));
+        assert!(uri3.path.is_empty());
+        assert_eq!(None, uri3.query);
+        assert_eq!(None, uri3.fragment);
+    }
+
+    #[test]
+    fn is_valid_mac_address_cases() {
+        assert!(is_valid_mac_address("01:23:45:67:89:Aa"));
+        assert!(is_valid_mac_address("Aa:Bb:Cc:Dd:Ee:Ff"));
+
+        assert!(!is_valid_mac_address(""));
+        assert!(!is_valid_mac_address("00:23:45"));
+        assert!(!is_valid_mac_address("00:23:45:Xx:Yy:Zz"));
+        assert!(!is_valid_mac_address("01-23-45-67-89-Aa"));
+        assert!(!is_valid_mac_address("01:23:45:67:89:Aa:Bb"));
+    }
+
+    #[test]
+    fn std_parse_basics() {
+        let u = parse(
+            "https://user:pw@example.com:8080/a%20b?q=1#frag",
+            ParseOptions::default(),
+        )
+        .unwrap();
+        assert_eq!(u.scheme, "https");
+        assert_eq!(u.user.as_ref().unwrap().as_str(), "user");
+        assert_eq!(u.password.as_ref().unwrap().as_str(), "pw");
+        assert_eq!(host(&u), "example.com");
+        assert_eq!(u.port, Some(8080));
+        assert_eq!(u.path.to_raw(), "/a b");
+        assert_eq!(u.query.as_ref().unwrap().as_str(), "q=1");
+        assert_eq!(u.fragment.as_ref().unwrap().as_str(), "frag");
+
+        let u = parse("file:///tmp/x", ParseOptions::default()).unwrap();
+        assert_eq!(u.host, None);
+        assert_eq!(u.path.as_str(), "/tmp/x");
+
+        let u = parse("http://[::1]:80/", ParseOptions::default()).unwrap();
+        assert_eq!(host(&u), "[::1]");
+        assert_eq!(u.port, Some(80));
+
+        assert_eq!(
+            parse("nocolon", ParseOptions::default()),
+            Err(ParseError::UnexpectedCharacter)
+        );
+        assert_eq!(
+            parse("file://a:b/", ParseOptions::default()),
+            Err(ParseError::InvalidPort)
+        );
+        assert_eq!(
+            parse("file://?x", ParseOptions::default()),
+            Err(ParseError::InvalidFormat)
+        );
+    }
+}
diff --git a/crates/ghostty-os/src/xdg.rs b/crates/ghostty-os/src/xdg.rs
new file mode 100644
index 0000000..51fae5b
--- /dev/null
+++ b/crates/ghostty-os/src/xdg.rs
@@ -0,0 +1,201 @@
+//! Implementation of the XDG Base Directory specification
+//! (https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html)
+
+use std::ffi::CStr;
+
+use crate::env::getenv_not_empty;
+use crate::{homedir, path_join};
+
+#[derive(Debug, Clone, Default)]
+pub struct Options<'a> {
+    /// Subdirectories to join to the base. This avoids extra allocations
+    /// when building up the directory. This is commonly the application.
+    pub subdir: Option<&'a str>,
+
+    /// The home directory for the user. If this is not set, we will attempt
+    /// to look it up which is an expensive process. By setting this, you can
+    /// avoid lookups.
+    pub home: Option<&'a str>,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("no home directory could be determined")]
+    NoHomeDir,
+}
+
+/// Get the XDG user config directory.
+pub fn config(opts: &Options<'_>) -> Result<String, Error> {
+    dir(opts, "XDG_CONFIG_HOME", ".config")
+}
+
+/// Get the XDG cache directory.
+pub fn cache(opts: &Options<'_>) -> Result<String, Error> {
+    dir(opts, "XDG_CACHE_HOME", ".cache")
+}
+
+/// Get the XDG state directory.
+pub fn state(opts: &Options<'_>) -> Result<String, Error> {
+    dir(opts, "XDG_STATE_HOME", ".local/state")
+}
+
+/// Unified helper to get XDG directories that follow a common pattern.
+fn dir(opts: &Options<'_>, env: &str, default_subdir: &str) -> Result<String, Error> {
+    // If we have a cached home dir, use that.
+    if let Some(home) = opts.home {
+        return Ok(path_join(&[
+            home,
+            default_subdir,
+            opts.subdir.unwrap_or(""),
+        ]));
+    }
+
+    // First check the env var.
+    if let Some(env) = getenv_not_empty(env) {
+        // If we have a subdir, then we join it.
+        if let Some(subdir) = opts.subdir {
+            return Ok(path_join(&[&env, subdir]));
+        }
+
+        return Ok(env);
+    }
+
+    // Get our home dir
+    if let Ok(Some(home)) = homedir::home() {
+        return Ok(path_join(&[
+            &home,
+            default_subdir,
+            opts.subdir.unwrap_or(""),
+        ]));
+    }
+
+    Err(Error::NoHomeDir)
+}
+
+/// Parses the xdg-terminal-exec specification. This expects argv[0] to
+/// be "xdg-terminal-exec".
+pub fn parse_terminal_exec<'a>(argv: &'a [&'a CStr]) -> Option<&'a [&'a CStr]> {
+    let first = argv.first()?.to_bytes();
+    let base = first.rsplit(|&b| b == b'/').next().unwrap_or(first);
+    if base != b"xdg-terminal-exec" {
+        return None;
+    }
+
+    // We expect at least one argument
+    if argv.len() < 2 {
+        return Some(&[]);
+    }
+
+    // If the first argument is "-e" we skip it.
+    let start = if argv[1].to_bytes() == b"-e" { 2 } else { 1 };
+    Some(&argv[start..])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn config_default() {
+        let value = crate::testutil::with_env_lock(|| config(&Options::default()).unwrap());
+        assert!(!value.is_empty());
+    }
+
+    #[test]
+    fn cache_directory_paths() {
+        let mock_home = "/Users/test";
+
+        // Test base path
+        let p = cache(&Options {
+            home: Some(mock_home),
+            ..Default::default()
+        })
+        .unwrap();
+        assert_eq!(p, "/Users/test/.cache");
+
+        // Test with subdir
+        let p = cache(&Options {
+            home: Some(mock_home),
+            subdir: Some("ghostty"),
+        })
+        .unwrap();
+        assert_eq!(p, "/Users/test/.cache/ghostty");
+    }
+
+    type DirFn = fn(&Options<'_>) -> Result<String, Error>;
+    const CASES: [(&str, DirFn, &str); 3] = [
+        ("XDG_CONFIG_HOME", config, ".config"),
+        ("XDG_CACHE_HOME", cache, ".cache"),
+        ("XDG_STATE_HOME", state, ".local/state"),
+    ];
+
+    #[test]
+    fn fallback_when_xdg_env_empty() {
+        let temp_home = "/tmp/ghostty-test-home";
+        for (name, func, default_subdir) in CASES {
+            temp_env::with_vars([("HOME", Some(temp_home)), (name, Some(""))], || {
+                let expected = path_join(&[temp_home, default_subdir]);
+                let actual = func(&Options::default()).unwrap();
+                assert_eq!(expected, actual);
+            });
+        }
+    }
+
+    #[test]
+    fn fallback_when_xdg_env_empty_and_subdir() {
+        let temp_home = "/tmp/ghostty-test-home";
+        for (name, func, default_subdir) in CASES {
+            temp_env::with_vars([("HOME", Some(temp_home)), (name, Some(""))], || {
+                let expected = path_join(&[temp_home, default_subdir, "ghostty"]);
+                let actual = func(&Options {
+                    subdir: Some("ghostty"),
+                    ..Default::default()
+                })
+                .unwrap();
+                assert_eq!(expected, actual);
+            });
+        }
+    }
+
+    #[test]
+    fn env_var_used_when_set() {
+        temp_env::with_vars([("XDG_CONFIG_HOME", Some("/x/cfg"))], || {
+            assert_eq!(config(&Options::default()).unwrap(), "/x/cfg");
+            let o = Options {
+                subdir: Some("ghostty"),
+                ..Default::default()
+            };
+            assert_eq!(config(&o).unwrap(), "/x/cfg/ghostty");
+        });
+    }
+
+    fn c(s: &str) -> std::ffi::CString {
+        std::ffi::CString::new(s).unwrap()
+    }
+
+    #[test]
+    fn parse_terminal_exec_cases() {
+        fn run(args: &[&str]) -> Option<Vec<String>> {
+            let owned: Vec<std::ffi::CString> = args.iter().map(|s| c(s)).collect();
+            let refs: Vec<&CStr> = owned.iter().map(std::ffi::CString::as_c_str).collect();
+            parse_terminal_exec(&refs)
+                .map(|s| s.iter().map(|x| x.to_str().unwrap().to_owned()).collect())
+        }
+
+        assert_eq!(run(&["a", "b", "c"]), None);
+        assert_eq!(run(&["xdg-terminal-exec"]), Some(vec![]));
+        assert_eq!(
+            run(&["xdg-terminal-exec", "a", "b", "c"]),
+            Some(vec!["a".into(), "b".into(), "c".into()])
+        );
+        assert_eq!(
+            run(&["xdg-terminal-exec", "-e", "a", "b", "c"]),
+            Some(vec!["a".into(), "b".into(), "c".into()])
+        );
+        assert_eq!(
+            run(&["xdg-terminal-exec", "a", "-e", "b", "c"]),
+            Some(vec!["a".into(), "-e".into(), "b".into(), "c".into()])
+        );
+        assert_eq!(run(&["/usr/bin/xdg-terminal-exec"]), Some(vec![]));
+    }
+}
diff --git a/docs/rewrite/notes/ghostty-os.md b/docs/rewrite/notes/ghostty-os.md
new file mode 100644
index 0000000..3acadc1
--- /dev/null
+++ b/docs/rewrite/notes/ghostty-os.md
@@ -0,0 +1,70 @@
+# ghostty-os notes
+
+Port of `ZIG/src/os/*` (Linux only) and `ZIG/src/file_type.zig`. `unsafe` is
+forbidden; deps: rustix, nix (user), zbus, gettext-rs (`gettextrs`), thiserror,
+log; dev: temp-env.
+
+## File -> module
+xdg, homedir, hostname, env, file, flatpak, i18n, i18n_locales, locale, open,
+passwd, path, pipe, resourcesdir, shell, string_encoding, systemd,
+TempDir (`temp_dir`), uri, desktop, kernel_info, cgroup, dbus, mouse, args,
+main (re-exports in `lib.rs`), `file_type` (from `src/file_type.zig`).
+
+## Skipped files
+macos.zig, mach.zig, cf_release_thread.zig, windows.zig, wasm.zig, wasm/*
+(macOS/Windows/WASM are out of scope). Windows/macOS branches inside ported
+files are dropped. `main.zig` exports `OpenType` (stale, nonexistent in
+open.zig) - not ported.
+
+## API shape deviations (buffers/allocators -> owned values)
+- Zig allocator/fixed-buffer APIs return `String`/`Option<String>`. Fixed
+  buffer overflow semantics kept only where tested: `homedir::home_with_capacity`
+  / `expand_home_with_capacity` (BufferTooSmall).
+- `env::getenv` returns `Option<String>` (no `GetEnvResult`); `setenv`/`unsetenv`
+  are NOT provided (unsafe in Rust 2024). Tests use `temp_env` (dev-dep).
+- `ShellEscapeWriter<W: io::Write>`, `ShellCommandBuilder::to_owned_slice` -> `CString`.
+- `string_encoding` take `impl io::Write`; error enum `{DecodeError, Io}`.
+- `uri`: own `Uri`/`Component` types replicating `std.Uri.parse` (Zig std not
+  available in Rust); `parse(text, ParseOptions)` as in Zig.
+- `cgroup::current(pid)` reads at most 4096 bytes (caller buffer in Zig).
+- `resourcesdir`: Zig `builtin.mode == .Debug` mapped to `cfg!(debug_assertions)`
+  (note: workspace `release` profile has debug-assertions on; `production` off).
+- `TempDir`: path-based (parent + name) rather than Dir handles; deletes on Drop;
+  `deinit(self)` provided. Dir created mode 0o755.
+- `file::fix_max_files` uses rustix rlimit; `None` == RLIM_INFINITY.
+- `systemd::notify`: a leading `@` in NOTIFY_SOCKET is now treated as an abstract
+  socket (Zig copied it literally, which can't work). Port otherwise 1:1.
+- `i18n::canonicalize_locale`: gnulib's `_libintl_locale_name_canonicalize` is
+  not available; pure-Rust approximation (zh fixes + `-` -> `_`). `tr()` ==
+  `_()` (dgettext on bundle id domain). `static_locale` is a `const fn` that
+  panics at compile time for unsupported locales. i18n always enabled.
+- `open::open(kind, url)`: local `OpenUrlKind` enum
+  (TODO(integration): apprt action kind). Snap handling keyed on `SNAP` env
+  instead of build flag.
+
+## Deferred / incomplete
+- **locale::ensure_locale is a no-op.** `setlocale` and `setenv` are unsafe;
+  no safe crate wraps them (`gettextrs::setlocale` is `unsafe fn`). gtk_init
+  calls `setlocale(LC_ALL, "")` on Linux. TODO(integration): if needed, perform
+  the libc call in an unsafe-allowed crate (steps documented in locale.rs).
+- **passwd Flatpak branch**: Zig shells out to host `getent passwd` via
+  FlatpakHostCommand + Pty. Needs ghostty-termio Pty -> TODO(integration);
+  currently warns and uses sandbox entry.
+- **FlatpakHostCommand**: implemented with `zbus` blocking API (HostCommand,
+  HostCommandSignal, HostCommandExited signal, fd passing) in a helper thread;
+  `waitXev` replaced by `wait_callback`. Compiles and the state machine/error
+  paths are tested, but the D-Bus path is UNTESTED (no Flatpak portal here).
+  Constructor `FlatpakHostCommand::new(argv, stdin, stdout, stderr)`; fds are
+  `OwnedFd` and dup'd on spawn.
+- `mouse::click_interval` is `None` on Linux (macOS only).
+
+## Tests
+Ported Linux-applicable Zig tests (all passing, 88 total incl. extras):
+xdg(5), homedir(2: expandHomeUnix, home), hostname(4), env(4), path(3),
+shell(1 builder + 7 escape), string_encoding(10 printf_q + singles_percent +
+7 percent), uri(3), desktop(1), kernel_info(1), args(1), passwd(1), TempDir(1),
+i18n canonicalize (darwin-only in Zig, run here against the approximation).
+Skipped: none of the Linux tests. Extras: path_join, file_type, systemd notify
+(real unix datagram socket), resourcesdir, pipe, uri/std parse, etc.
+Zig tests that mutate env were rewritten with `temp_env::with_vars`; tests that
+read PATH/HOME take the same lock via `testutil::with_env_lock`.