The s6-svlisten1 program
s6-svlisten1 runs a program while listening on notifications from a
supervised service, and blocks until said service goes up, or down.
s6-svlisten1 only waits for notifications; it never polls.
s6-svlisten1 [ -U | -u | -D | -d | -r | -R ] [ -t timeout ] servicedir prog...
- s6-svlisten1 checks the state of the servicedir
service directory and monitor its
- It spawns prog... as a child right after getting the
initial state of the service.
- It then blocks until the wanted state happens.
- 0: success, the wanted state has been reached
- 1: the service was supposed to go up, but reported permanent failure
- 99: timed out
- 100: wrong usage
- 111: system call failed
- -u : up. s6-svlisten1 will wait until the service is up, as
reported by s6-supervise.
This is the default; it is not reliable, but it does not depend on specific
support in the service programs. See this page
- -U : really up. s6-svlisten1 will wait until the service is
up and ready as reported by the daemon itself. This requires
specific support in the service programs, and the use of the
notification-fd file in the
See the explanation on this page.
- -d : down. s6-svlisten1 will wait until the service is down.
- -D : really down. s6-svlisten1 will wait until the
service is down and the cleanup script in servicedir/finish
has finished executing (or has timed out and been killed).
- -r : restart. s6-svlisteni1 will wait until
the service has been started or restarted, i.e. they have been in the
down state, then the up state.
- -R : restart and ready. s6-svlisten1 will wait until
the service has been started or restarted and has notified
- -t timeout : if the requested event has not
happened after timeout milliseconds, s6-svlisten1 will print a message
to stderr and exit 99. By default, timeout is 0, which means no time
- s6-svlisten1 is the service-specific version of
s6-ftrig-listen1. The point of s6-svlisten1
is to use it to spawn a program such as s6-svc,
in order to send signals to a service while making sure to catch its
state changes - thus avoiding the race condition that occurs when running
s6-svc then s6-svwait
- The s6-svlisten program is an extension
of s6-svlisten1. It can watch the state of several services at once; however,
its syntax makes it best used in execline