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make systemd launch detection smarter

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This commit is contained in:
Jeffrey C. Ollie
2024-07-29 10:47:10 -05:00
parent ee18838fc7
commit 28888bbf9f
1 changed files with 45 additions and 6 deletions
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51
src/os/systemd.zig
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@ -1,6 +1,12 @@
const std = @import("std");
const builtin = @import("builtin");
const log = std.log.scoped(.systemd);
const c = @cImport({
@cInclude("unistd.h");
});
/// Returns true if the program was launched as a systemd service.
///
/// On Linux, this returns true if the program was launched as a systemd
@ -9,12 +15,45 @@ const builtin = @import("builtin");
/// For other platforms and app runtimes, this returns false.
pub fn launchedBySystemd() bool {
return switch (builtin.os.tag) {
// On Linux, systemd sets the `INVOCATION_ID` (v232+) and the
// `JOURNAL_STREAM` (v231+) enviroment variables. If these environment
// variables are present (no matter the value) we were launched by
// systemd. This can be fooled if Ghostty is launched from another
// terminal that does not clean up these environment variables.
.linux => std.posix.getenv("INVOCATION_ID") != null and std.posix.getenv("JOURNAL_STREAM") != null,
.linux => linux: {
// On Linux, systemd sets the `INVOCATION_ID` (v232+) and the
// `JOURNAL_STREAM` (v231+) enviroment variables. If these
// environment variables are not present we were not launched by
// systemd.
if (std.posix.getenv("INVOCATION_ID") == null) break :linux false;
if (std.posix.getenv("JOURNAL_STREAM") == null) break :linux 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.
const ppid = c.getppid();
// If the parent PID is 1 we'll assume that it's `systemd` as other init systems
// are unlikely.
if (ppid == 1) break :linux 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>/exe` symlink
// to see if it ends with `/systemd`.
var path_buf: [std.fs.max_path_bytes]u8 = undefined;
const path = std.fmt.bufPrint(&path_buf, "/proc/{d}/exe", .{ppid}) catch {
log.err("unable to format path to exe {d}", .{ppid});
break :linux false;
};
var link_buf: [std.fs.max_path_bytes]u8 = undefined;
const link = std.fs.readLinkAbsolute(path, &link_buf) catch {
log.err("unable to read link '{s}'", .{path});
break :linux false;
};
if (std.mem.endsWith(u8, link, "/systemd")) break :linux true;
break :linux false;
},
// No other system supports systemd so always return false.
else => false,