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supervise.8
supervise - starts and monitors a service.
supervise s
supervise(8) switches to the directory named s and starts ./init if it exists. It restarts ./init if ./init exits with non-zero status. It pauses for a second after starting ./init, so that it does not loop too quickly in case ./init exits immediately. directory has to be relative to the current working directory and cannot start with the dot (.) or the slash (/) character.
After ./init exits with zero exit status, supervise(8) starts ./run. It restarts ./run if ./run exits. It pauses for a second after starting ./run, so that it does not loop too quickly in case ./run exits immediately.
If the file s/down exists, supervise(8) does not start ./run immediately. You can use svc(8) to start ./run or to give other commands to supervise(8). supervise uses s/supervise/control fifo to read these commands.
if the file s/shutdown exists supervise(8) executes shutdown when asked to exit.
if the file s/alert exists supervise(8) executes alert whenever run exits. The pid of the process that exited is passed as the first argument to alert. The exit value or signal (if killed by signal) is passed as the second argument to alert. The third argument is either exited or stopped / signalled.
supervise(8) creates the directory s/supervise in run/svscan where run is either /run or /var/run, depending on your operating system. supervise(8) maintains status information in a binary format in the directory s/supervise. The directory s must be writable to supervise(8). The status information can be read by svstat(8).
supervise(8) may exit immediately after startup if it cannot find the files it needs in s or if another copy of supervise(8) is already running in s. Once supervise(8) is successfully running, it will not exit unless it is killed or specifically asked to exit. Once supervise(8) is successfully running, it opens the fifo s/supervise/ok in O_RDONLY|O_NDELAY mode. You can use svok(8) to check whether supervise(8) is successfully running. You can use svscan(8) to reliably start a collection of supervise(8) processes. svscan mirrors the service directory in /run or /var/run directory (whichever is found first). So /run/s will be analogous to /service/s. When started by svscan, error messages printed by supervise(8) will go the standard error output of svscan(8) process.
supervise(8) can wait for another service by having a file named s/wait. This file has two lines. The first line is time t in seconds and the second line is service name w. w refers to the service which service s should wait t secs after service w starts up. The amount of time t is limited to a max of 32767 secs. Any value above this value will be limited to 60 secs. supervise(8) opens w/supervise/up in write mode. If service w is up, the write returns immediately. If service w is done, write will block till w is up and running.
supervise(8) creates the following FIFOs for with O_RDONLY|O_NDELAY mode. See open(2) for description of O_RDONLY, O_NDELAY
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s/supervise/control - for reading commands from clients like svc(8).
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s/supervise/ok - clients can open this in write mode (O_WRONLY) to test if supervise(8) is running in s. If write returns, it means supervise(8) is running.
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s/supervise/up - clients can open this in write mode (O_WRONLY) to test if service s is up. Any client that opens this fifo will block until the service s is up. If write returns, it means service s(8) is running.
svc(8), svok(8), svstat(8), svps(1), svscanboot(8), svscan(8), svctool(8), minisvc(8), readproctitle(8), fghack(8), pgrphack(8), multilog(8), tai64n(8), tai64nlocal(8), setuidgid(8), envuidgid(8), envdir(8), softlimit(8), setlock(8), open(2)