s6
Software
skarnet.org

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.

Interface

     s6-svc [ -abqhkti12fFpcoduxO ] 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.

Options

• -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
• -o : once. Equivalent to "-uO".
• -d : down. If the supervised process is up, send it a SIGTERM and a SIGCONT. Do not restart it.
• -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, supervise will exit too. This command should normally never be used on a working system.
• -O : Once at most. Do not restart the supervised process when it dies. If it is down when the command is received, do not even start it.
• -f, -F : unused for now.

Usage examples

 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 configuration file.

 s6-svc -t /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 -d /service/ftpd 

Take down the ftpd server.

 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.

Internals

s6-svc writes control commands into the servicedir/supervise/control FIFO. A s6-supervise process running on servicedir will be listening to this FIFO, and will read and interpret those commands.