s6
Software
skarnet.org

The s6-svscanctl program

s6-svscanctl sends commands to a running s6-svscan process.

Interface

     s6-svscanctl [ -zabhitqnN ] scandir

s6-svscanctl sends the given series of commands to the s6-svscan process monitoring the scandir directory, then exits 0. It exits 111 if it cannot send a command, or 100 if no s6-svscan process is running on scandir.

Options

• -z : destroy zombies. Immediately triggers s6-svscan's reaper mechanism.
• -a : Alarm. s6-svscan will immediately perform a scan of scandir to check for services.
• -b : abort. s6-svscan will exec into its finishing procedure. It will not kill any of the maintained s6-supervise processes, unless a t or q option is also present before the b option in the s6-svscanctl invocation.
• -h : Reload configuration. s6-svscan will perform a scan, and destroy inactive services. Equivalent to -an.
• -i : equivalent to -t below.
• -t : Terminate. s6-svscan will send a SIGTERM to all the s6-supervise processes supervising a service and a SIGHUP to all the s6-supervise processes supervising a logger, then exec into its finish procedure. This means that services will be brought down but loggers will exit naturally on EOF, and s6-svscan will wait for them to exit before exec'ing into .s6-svscan/finish or exiting itself: it's a clean shutdown with no loss of logs.
• -q : Quit. s6-svscan will send all its s6-supervise processes a SIGTERM, then exec into its finish procedure. This is different from -t in that services and loggers will be forcibly killed, so the quit procedure may be faster but in-flight logs may be lost.
• -n : nuke. s6-svscan will kill all the s6-supervise processes it has launched but that did not match a service directory last time scandir was scanned, i.e. it prunes the supervision tree so that it matches exactly what was in scandir at the time of the last scan. A SIGTERM is sent to the s6-supervise processes supervising services and a SIGHUP is sent to the s6-supervise processes supervising loggers.
• -N : Really nuke. Does the same thing as -n, except that SIGTERM is sent to all the relevant s6-supervise processes, even if they are supervising loggers. This is not recommended in a situation where you do not need to tear down the supervision tree.

Internals

s6-svscanctl writes control commands into the scandir/.s6-svscan/control FIFO. An s6-svscan process running on scandir will be listening to this FIFO, and will read and interpret those commands.