| monitor - Manage a daemon process, restarting if it exits |
| monitor [ options ] cmd [ arg ... ] |
| The monitor utility manages a child process. The monitor restarts the child if it exits and logs child startups and terminations via syslog. Use of a monitor process gives added assurance that a service will be continuously available and that there will be notification if it fails. |
| If the monitor receives SIGTERM (or SIGINT), it sends SIGTERM to the child and then exits itself. If it receives another of these after commencing a kill of its child process, it sends the child SIGKILL. In other words killing the monitor process twice forces a hard kill of the child. In any case the monitor process does not exit until it has confirmation that the child has terminated, which helps make service stop-then-start sequences more reliable. |
| If the monitor receives SIGHUP it forwards the signal to the child process, By convention this requests a reload of its configuration files. If the child is unprepared for SIGHUP, the signal will kill it, but the monitor will still restart it. |
| The monitor program writes a file /tmp/<service-name>.<pid>.status, currently just a caution message during child startups. Startstop(8) reads this file for service status information. |
| It logs child process startups and terminations to syslog at the LOG_NOTICE level, using the LOG_DAEMON facility. If the child exits (except when being killed by its monitor), it logs child termination at the LOG_ERR level. Child restarts include a two-second delay after the child has terminated, to limit the rate of process spawning. |
| -n service_name |
| The monitor includes the service name in syslog messages and in the filename of its status file. If no name is given, it uses the base name of the command. |
| -e |
| With the -e option, the monitor makes the child's stderr a duplicate of its stdout. Error messages from monitor itself go to the original stderr. |
| startstop(8), setuser(8) |