The s6-svc program
s6-svc sends commands to a running s6-supervise
process. In other words, it's used to control a supervised process; among
other benefits, it allows an administrator to send signals to daemons without
knowing their PIDs, and without using horrible hacks such as .pid files.
s6-svc [ -wu | -wU | -wd | -wD | -wr | -wR ] [ -T timeout ] [ -abqhkti12pcyoduxOr ] servicedir
s6-svc sends the given series of commands to the
s6-supervise process monitoring the
servicedir directory, then exits 0. It exits 111 if it cannot send
a command, or 100 if no s6-supervise process is running on servicedir.
- -a : send a SIGALRM to the supervised process
- -b : send a SIGABRT to the supervised process
- -q : send a SIGQUIT to the supervised process
- -h : send a SIGHUP to the supervised process
- -k : send a SIGKILL to the supervised process
- -t : send a SIGTERM to the supervised process
- -i : send a SIGINT to the supervised process
- -1 : send a SIGUSR1 to the supervised process
- -2 : send a SIGUSR2 to the supervised process
- -p : send a SIGSTOP to the supervised process
- -c : send a SIGCONT to the supervised process
- -y : send a SIGWINCH to the supervised process
- -o : once. Equivalent to "-uO".
- -d : down. If the supervised process is up, send it
a SIGTERM (by default) then a SIGCONT (to make sure even stopped processes
receive the signal aimed to kill them) and do not restart it.
The SIGTERM default can be changed by editing the ./down-signal
file in the service directory.
- -u : up. If the supervised process is down, start it.
Automatically restart it when it dies.
- -x : exit. When the service is asked to be down and
the supervised process dies, s6-supervise will exit too. This command should
normally never be used on a working system. Note that if this command is
sent and a ./finish script exists for the service, the last
./finish invocation before
s6-supervise exits will run with its stdin
and stdout redirected to /dev/null.
- -O : mark the service to run once at most. iow: do not
restart the supervised process when it dies. If it is down when the command
is received, do not even start it.
- -r : If the service is up, restart it, by sending it a
signal to kill it and letting s6-supervise
start it again. By default, the signal is a SIGTERM; this can be configured
via the ./down-signal file in the service
- -T timeout : if the -wstate
option has been given, -T specifies a timeout
(in milliseconds) after which s6-svc will exit 1 with an error message if
the service still hasn't reached the desired state. By default, the
timeout is 0, which means that s6-svc will block indefinitely.
- -wd : s6-svc will not exit until the service is down,
i.e. until the run process has died.
- -wD : s6-svc will not exit until the service is down
and ready to be brought up, i.e. a possible finish script has
- -wu : s6-svc will not exit until the service is up,
i.e. there is a process running the run executable.
- -wU : s6-svc will not exit until the service is up and
ready as notified by the daemon itself.
If the service directory does not contain
a notification-fd file to tell
s6-supervise to accept readiness
notification, s6-svc will print a warning and act as if the -wu
option had been given instead.
- -wr : s6-svc will not exit until the service has been
started or restarted.
- -wR : s6-svc will not exit until the service has been
started or restarted and has notified readiness.
s6-svc -h /service/httpd
Send a SIGHUP to the process represented by the /service/httpd
service directory. Traditionally, this makes web servers reload their
s6-svc -r /service/sshd
Kill (and automatically restart, if the wanted state of the service is up)
the process represented by the /service/sshd service directory -
typically the sshd server.
s6-svc -wD -d /service/ftpd
Take down the ftpd server and block until the process is down and
the finish script has completed.
s6-svc -wU -T 5000 -u /service/ftpd
Bring up the ftpd server and block until it has sent notification that it
is ready. Exit 1 if it is still not ready after 5 seconds.
s6-svc -wR -t /service/ftpd
Send a SIGTERM to the ftpd server; wait for
s6-supervise to restart it, and block
until it has notified that it is ready to serve again. See the NOTES
section below for a caveat.
s6-svc -a /service/httpd/log
Send a SIGALRM to the logger process for the httpd server. If this logger
process is s6-log, this triggers a log rotation.
- s6-svc writes control commands into the servicedir/supervise/control
FIFO. An s6-supervise process running on servicedir will be listening to this FIFO,
and will read and interpret those commands.
- When invoked with one of the -w options, s6-svc executes into
s6-svlisten1, which will listen to service state
changes and spawn another s6-svc instance (without the -w option)
that will send the commands to the service. Any error message written during
the waiting period will mention it is being written by s6-svlisten1; this is normal.
- The -t and -r options make s6-supervise
send a signal to the service if it is up; but if the service is currently down,
they do nothing, and in particular they do not instruct s6-supervise to bring the
service up. Consequently, s6-svc -rwr servicedir may wait forever
for the service to be up, if it is currently wanted down. To avoid that, make sure
your service is wanted up by using s6-svc -ruwr servicedir instead.