Avery Payne:
I have been giving the "one shot" question considerable thought. I
have a
number of scripts that require this kind of behavior, so it's of great
interest to me. The current methods that I have encountered are:
+ use a pause(1) command that simply sleeps forever on a subset of
signals,
then terminates; this effectively holds the script
+ as per discussion elsewhere on the mailing list, have the script send a
signal to itself to make it go to sleep (untested)
nosh has a built-in pause(1) command, created for this very purpose. It
is used in run scripts created by convert-systemd-units if a systemd
service unit has Type=oneshot and RemainAfterExit=false. However, nosh
has a third option that you haven't listed.
If a systemd service unit has RemainAfterExit=true, irrespective of
type, then instead convert-systemd-units makes use of the "run_on_empty"
mechanism in service-manager(1), where a file named "remain" in the
service/ directory causes the service manager not to automatically leave
the RUNNING state when the daemon process exits. One sees this with the
pre-supplied standard targets, which are in the running state but have
no process ID:
JdeBP %systemctl status
{basic,local-fs,multi-user,normal,server,sysinit,workstation,virtualbox}.target
sshd.service
/etc/system-manager/targets/basic: running 3d 4h 55m 12s ago
/etc/system-manager/targets/local-fs: running 3d 4h 55m 17s ago
/etc/system-manager/targets/multi-user: running 3d 4h 55m 11s ago
/etc/system-manager/targets/normal: running 3d 4h 55m 11s ago
/etc/system-manager/targets/server: running 3d 4h 55m 11s ago
/etc/system-manager/targets/sysinit: running 3d 4h 55m 19s ago
/etc/system-manager/targets/workstation: running 3d 4h 55m 11s ago
/etc/system-manager/targets/virtualbox: running 3d 4h 55m 10s ago
/var/sv/sshd: running (pid 220) 3d 4h 55m 49s ago
JdeBP %
