How to make sure an application keeps running on Linux

Question

I have used a simple script with cron to make sure that the program is running. If it is not, then it will start it up. This may not be the perfect solution you are looking for, but it is simple and works rather well.

#!/bin/bash
#make-run.sh
#make sure a process is always running.

export DISPLAY=:0 #needed if you are running a simple gui app.

process=YourProcessName
makerun="/usr/bin/program"

if ps ax | grep -v grep | grep $process > /dev/null
then
    exit
else
    $makerun &
fi

exit

Then add a cron job every minute, or every 5 minutes.

Monit is perfect for this :)

You can write simple config files which tell monit to watch e.g. a TCP port, a PID file etc

monit will run a command you specify when the process it is monitoring is unavailable/using too much memory/is pegging the CPU for too long/etc. It will also pop out an email alert telling you what happened and whether it could do anything about it.

We use it to keep a load of our websites running while giving us early warning when something's going wrong.

-- Your faithful employee, Monit

Notice: Upstart is in maintenance mode and was abandoned by Ubuntu which uses systemd. One should check the systemd' manual for details how to write service definition.

Since you're using Ubuntu, you may be interested in Upstart, which has replaced the traditional sysV init. One key feature is that it can restart a service if it dies unexpectedly. Fedora has moved to upstart, and Debian is in experimental, so it may be worth looking into.

This may be overkill for this situation though, as a cron script will take 2 minutes to implement.

#!/bin/bash
if [[ ! `pidof -s yourapp` ]]; then
    invoke-rc.d yourapp start
fi

If you are using a systemd-based distro such as Fedora and recent Ubuntu releases, you can use systemd's "Restart" capability for services. It can be setup as a system service or as a user service if it needs to be managed by, and run as, a particular user, which is more likely the case in OP's particular situation.

The Restart option takes one of no, on-success, on-failure, on-abnormal, on-watchdog, on-abort, or always.

To run it as a user, simply place a file like the following into ~/.config/systemd/user/something.service:

[Unit]
Description=Something

[Service]
ExecStart=/path/to/something
Restart=on-failure

[Install]
WantedBy=graphical.target

then:

systemctl --user daemon-reload
systemctl --user [status|start|stop|restart] something

No root privilege / modification of system files needed, no cron jobs needed, nothing to install, flexible as hell (see all the related service options in the documentation).

See also https://wiki.archlinux.org/index.php/Systemd/User for more information about using the per-user systemd instance.

I have used from cron "killall -0 programname || /etc/init.d/programname start". kill will error if the process doesn't exist. If it does exist, it'll deliver a null signal to the process (which the kernel will ignore and not bother passing on.)

This idiom is simple to remember (IMHO). Generally I use this while I'm still trying to discover why the service itself is failing. IMHO a program shouldn't just disappear unexpectedly :)

Put your run in a loop- so when it exits, it runs again... while(true){ run my app.. }

I couldn't get Chris Wendt solution to work for some reason, and it was hard to debug. This one is pretty much the same but easier to debug, excludes bash from the pattern matching. To debug just run: bash ./root/makerun-mysql.sh. In the following example with mysql-server just replace the value of the variables for process and makerun for your process.

• Create a BASH-script like this (nano /root/makerun-mysql.sh):

#!/bin/bash
process="mysql"
makerun="/etc/init.d/mysql restart"
if ps ax | grep -v grep | grep -v bash | grep --quiet $process
then
    printf "Process '%s' is running.\n" "$process"
    exit
else
    printf "Starting process '%s' with command '%s'.\n" "$process" "$makerun"
    $makerun
fi
exit

• Make sure it's executable by adding proper file permissions (i.e. chmod 700 /root/makerun-mysql.sh)

• Then add this to your crontab (crontab -e):

# Keep processes running every 5 minutes
*/5 * * * * bash /root/makerun-mysql.sh