Tutorial
How To Write a Bash Script To Restart Server Programs
To ensure that the most imperative programs remain online as much as possible (even after a server crash or reboot), one can create a short bash script to check if the program is running, and if it is not, to launch it. By using cron to schedule the script to be executed on a regular basis, we can make sure that program relaunches whenever it goes down.
Bash Script
The first step in this process is to create the script itself. There are a variety of programs such as upstart, supervisor, and monit, that have the capability to start and monitor applications on a virtual private server in a very nuanced way— this bash script will simply provide an on switch.
Below is a sample script that starts apache if it finds it off.
nano launch.sh
#!/bin/sh
ps auxw | grep apache2 | grep -v grep > /dev/null
if [ $? != 0 ]
then
/etc/init.d/apache2 start > /dev/null
fi
Once you have saved the script, you must give it executable permissions in order to be able to run it:
chmod +x launch.sh
Apache can be replaced with any required application. Should you want to set up the script for a variety of applications, you can create a new script for each one, placing it on its own line in the cron file.
Cron Setup
With the script in hand, we need to set up the schedule on which it will run. The cron utility allows us to schedule at what intervals the script should execute. Start by opening up the cron file:
crontab -e
Cron has a detailed explanation of how the timing system works at the beginning.
Once you know how often you want the script to run, you can write in the corresponding line.
The most often that the script can run in cron is every minute. Should you want to set up such a small increment, you can use this template:
* * * * * ~/launch.sh
Every five minutes would be set up like this:
*/5 * * * * ~/launch.sh
See More
Setting up this simple script will keep the program starting up after it shuts down for any reason. This is convenient as it will ensure that the longest time that a program will be down is for the interval of time that you specified in the cron configuration.
Should you need a program that is even slightly more subtle, you can set up the details of your startup with one of the several server monitoring programs (Supervisor, Upstart, or Monit).
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Don’t you need to make sure that the script is executable by doing something like u+x ~/launch.sh?
@Marc: That is correct, I’ve updated the article. Thanks!
I’m using this script to restart mysql with no luck. Log says
@robert: Can you pastebin the contents of
/root/mysql-check.sh?I’m trying to utilise this script and crontab to keep an eye on MySQL.
I couldn’t get the script to work.
I’m very inexperienced with this stuff but reviewing the above shouldn’t it be:
I’m not really sure the significance of the $? in the above though I would assume it’s a print of the output from the previous command.
I’m probably wrong here but if MySQL is down and thus not printed in ps auxw and we’re removing the grep process too then isn’t an output of nothing what should be triggering the process restart?
EDIT: No that still doesn’t solve the problem. If I use = 0 the service reboots at every run of the script. If I use != 0 then the service never reboots. Confused.
Anyone able to help on this?
Thanks for the tutorial of how to make a bash script. However for this case I would prefer something like “service apache2 status || service apache2 start” directly on the crontab line. I saw that trick here https://www.digitalocean.com/community/questions/how-do-you-check-mysql-status-via-cron?answer=18288
hello i add the commande and when i try to add cron tab i got this ? */1 * * * * ~/launch.sh -bash: */1: No such file or directory
Sorry but it does not work… It doesn’t restart my programs…
Some problem here too.
My script works just fine. It is in /etc/apache2/relaunch.sh, file permissions are
here’s the script
I try to run it from root’s cron. Here’s the cron entry.
Strangely, the script fires every minute and writes an entry into my log file without a problem, but won’t work correctly when it is run from Cron. Is it some problem with environment variable? Maybe I need to set that in the script too?
If I stop Apache, the script still writes the the log file but doesn’t restart Apache.