Skip to content
mon(1) - Simple single-process process monitoring program written in C
C Makefile Shell
Branch: master
Clone or download
tj Merge pull request #48 from dwoske/master
issue #47 : add fflush(stdout) to log method
Latest commit 9754dc2 Sep 7, 2016
Type Name Latest commit message Commit time
Failed to load latest commit information.
deps update commander Jan 8, 2013
.gitignore Initial commit Apr 12, 2012
.travis.yml Add basic .travis.yml for c Dec 3, 2013 Release 1.2.3 Dec 1, 2013
Makefile Makefile: improve compatibility with BSD make. Dec 1, 2013 Update install command for tg not visionmedia Jun 14, 2016
package.json Release 1.2.2 Jun 10, 2013


Super-simple monitoring program.

mon spawned from the needlessly complex frustration that tools like monit provide, with their awkward DSLs and setup. mon is written in C, uses less than 400kb of memory, and is incredibly simple to set up.


$ make install

Too lazy to clone?:

$ (mkdir /tmp/mon && cd /tmp/mon && curl -L# | tar zx --strip 1 && make install && rm -rf /tmp/mon)


Usage: mon [options] <command>


  -V, --version                 output program version
  -h, --help                    output help information
  -l, --log <path>              specify logfile [mon.log]
  -s, --sleep <sec>             sleep seconds before re-executing [1]
  -S, --status                  check status of --pidfile
  -p, --pidfile <path>          write pid to <path>
  -m, --mon-pidfile <path>      write mon(1) pid to <path>
  -P, --prefix <str>            add a log prefix
  -d, --daemonize               daemonize the program
  -a, --attempts <n>            retry attempts within 60 seconds [10]
  -R, --on-restart <cmd>        execute <cmd> on restarts
  -E, --on-error <cmd>          execute <cmd> on error


The most simple use of mon(1) is to simply keep a command running:

$ mon ./myprogram
mon : pid 50395
mon : child 50396
mon : sh -c "./example/"

You may daemonize mon and disassociate from the term with -d:

$ mon ./myprogram -d
mon : pid 50413

Failure alerts

mon(1) will continue to attempt restarting your program unless the maximum number of --attempts has been exceeded within 60 seconds. Each time a restart is performed the --on-restart command is executed, and when mon(1) finally bails the --on-error command is then executed before mon itself exits and gives up.

For example the following will echo "hey" three times before mon realizes that the program is unstable, since it's exiting immediately, thus finally invoking ./, or any other script you like.

mon "echo hey" --attempts 3 --on-error ./
mon : child 48386
mon : sh -c "echo hey"
mon : last restart less than one second ago
mon : 3 attempts remaining
mon : child 48387
mon : sh -c "echo hey"
mon : last restart less than one second ago
mon : 2 attempts remaining
mon : child 48388
mon : sh -c "echo hey"
mon : last restart less than one second ago
mon : 1 attempts remaining
mon : 3 restarts within less than one second, bailing
mon : on error `sh`
emailed failure notice to
mon : bye :)

NOTE: The process id is passed as an argument to both --on-error and --on-restart scripts.

Managing several mon(1) processes

mon(1) is designed to monitor a single program only, this means a few things, firstly that a single mon(1) may crash and it will not influence other programs, secondly that the "configuration" for mon(1) is simply a shell script, no need for funky weird inflexible DSLs.

#!/usr/bin/env bash


mon -d redis-server -p $pids/
mon -d "node $app/app" -p $pids/
mon -d "node $app/jobs" -p $pids/
mon -d "node $app/jobs" -p $pids/
mon -d "node $app/jobs" -p $pids/
mon -d "node $app/image" -p $pids/
mon -d "node $app/image" -p $pids/
mon -d "node $app/image-broker" -p $pids/

I highly recommend checking out jgallen23's mongroup(1), which provides a great interface for managing any number of mon(1) instances.


By default mon(1) logs to stdio, however when daemonized it will default to writing a log file named ./mon.log. If you have several instances you may wish to --prefix the log lines, or specify separate files.


  • SIGQUIT graceful shutdown
  • SIGTERM graceful shutdown


Tools built with mon(1):



Build Status

Build Status

You can’t perform that action at this time.