Clarify how to autostart with systemd after new security model

[heyzec]

Version Information:

• Distribution: NixOS
• swhkd version: Simple-Wayland-HotKey-Daemon 1.3.0-dev, built off c5c4071

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After #270, the docs at https://github.com/waycrate/swhkd/tree/main/contrib/init/systemd for autostarting swhkd/swhks using systemd is outdated because pkexec is not longer required.

I tried to create a systemd service that starts swhkd on its own (while swhks is started by my compositor). However, once any keybind is triggered, swhkd coredumps and crashes:

Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z TRACE swhkd] Logger initialized.
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd::perms] Setting EGID...
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd::perms] Setting EUID...
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd::perms] Setting initgroups...
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd] Wating for server to start...
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z INFO  swhkd] Env refreshed
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z TRACE swhkd] Environment Aquired
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z TRACE swhkd] Setting process umask.
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z TRACE swhkd] Reading /run/user/1000/swhkd_4294967295.pid file and checking for running instances.
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd] Previous PID: 6644
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd] Using config file path: "/home/heyzec/.config/swhkd/swhkdrc"
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z DEBUG swhkd] 1 Keyboard device(s) detected.
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z ERROR swhkd] Could not open evdev device at /dev/input/mouse0: Inappropriate ioctl for device (os error 25)
Sep 06 12:49:50 devpad swhkd-start[17859]: [2025-09-06T04:49:50Z TRACE swhkd] Other: swhkd switches virtual output
...omitted...
Sep 06 13:07:36 devpad systemd-coredump[33005]: [🡕] Process 17859 (swhkd) of user 0 dumped core.
                                                
                                                Module /nix/store/1bdckwi5ki5n3mw589l99h8j9vbslazd-swhkd-c5c4071459a6465a3743a8bb5bb990e27cdf315b/bin/swhkd without build-id.
                                                Module libcap.so.2 without build-id.
                                                Module libgcc_s.so.1 without build-id.

From above, swhkd is using /run/user/1000/swhkd_4294967295.pid as the IPC socket. From

swhkd/swhkd/src/daemon.rs

Line 650 in c5c4071

fn get_uid() -> Result<u32, Box<dyn Error>> {

we see 4294967295 (equivalent to -1 for 32-bit unsigned) is obtained from /proc/{}/loginuid. Login UID is unset when launched directly from systemd.

[andycandy-dev]

see #324 #325