The s6-svunlink program

s6-svunlink unlinks a service directory from a scan directory, then notifies s6-svscan that a service has been unregistered. It waits until the s6-supervise supervisor process managing the service has disappeared, then exits.

The point of s6-svunlink is to help integrate service directories into an existing service manager sequence and eliminate race conditions.

Interface

     s6-svunlink [ -X ] [ -t timeout ] scandir name

s6-svunlink expects a running s6-svscan process on scandir and a fully functional supervised service on service directory in scandir/name, which must be a symbolic link to a real directory located somewhere else.
It deletes the scandir/name symlink.
It sends a command to s6-svscan to signal it that a service has disappeared.
It waits for the s6-supervise process managing the service directory to exit.
It exits 0.

Exit codes

0: success
100: wrong usage
111: system call failed

Options

-X : don't wait. s6-svunlink will exit right away, without waiting for the supervisor to exit first.
-t timeout : if the supervisor has not exited after timeout milliseconds, s6-svlink will still exit. The default is 0, meaning no time limit..

Notes

Using s6-svlink to stop services is a suboptimal pattern: starting and stopping supervisors is a heavier operation than just stopping services. The simpler, more efficient pattern is to simply perform s6-svc -dwD scandir/name, which only commands, and waits for, the death of the service, without impacting the supervisor. Nevertheless, for symmetry with s6-svlink, this program is provided.
s6-svunlink is a destructor; as is, it returns 0 even in situations that are nominally a failure. For instance, it returns 0 even if its timeout expires; the rationale is that there is no sensible action for the user to do if this error is reported. s6-svunlink only reports errors when they uncover a deeper problem in the system.