Shell script issue: cron job script to Restart MySQL server when it stops accidentally

Question

I have this script, I am using it to setup CRON job to execute this script, so it can check if MySQL service is running; if not then it restart the MySQL service:

#!/bin/bash
service mysql status| grep 'mysql start/running' > /dev/null 2>&1
if [ $? != 0 ]
then
    sudo service mysql restart
fi

I have setup cron job as.

sudo crontab -e

and then added,

*/1 * * * * /home/ubuntu/mysql-check.sh

Problem is that it restart MySQL on every cron job execution.. even if server is running it restart the MySQL service what is correction in the script to do that.

why do you have a \\ in front of your shebang? If it's there to keep it from looking like a comment, then it's unnecessary. Shebangs are treated special like by Bash, as in they don't need to be escaped because they aren't comments in the sense that a comment is a piece of code that is not evaluated at all. — Alexej Magura, Apr 21 '14 at 06:37
Also, avoid using [ ... ] or test <TEST> in Bash. They're deprecated syntax. Use [[ ... ]] instead. Only use [ ... ] and/or test <TEST> when [[ ... ]] is not available. — Alexej Magura, Apr 21 '14 at 06:43
this is first shell script I tried by using some available scripts, I just modified it. don't know much about syntax. problem is still there mysql restarts on every CRON job execution @AlexejMagura — Vaibhav Dhage, Apr 21 '14 at 07:09
Try something like this: if ! (service mysql status | grep 'mysql start/running' &>/dev/null); then sudo service mysql restart; fi What this does, is it starts up a subshell, wherein service mysql status | grep 'mysql start/running' &> /dev/null gets run, the return (exit) status of said subshell then gets passed to the if-statement, which then checks to see if it is non-zero, and if it is not non-zero then it runs the then block. — Alexej Magura, Apr 21 '14 at 07:17
Doesn't mysql write its process pid to pid file? If it does you could use that as another way to check your mysql status — Flint, Apr 21 '14 at 07:57
Quite a long time ago, MySQL installation came with the default script called safe_mysqld or something like this (I don't remember details anymore) that was used to start the service. This script itself was monitoring the service and restarting it if it happens to crash. Is it no more the case? — raj, Sep 10 '21 at 07:59

Radu Rădeanu · Accepted Answer · 2014-08-22T17:11:08.257

20

I suspect that you setup the cron job to execute this script in your crontab file, and not in the root crontab file. This is not correct because if you don't run service mysql status as root, the mysql service will not be recognized.

So, modify the script as follow:

#!/bin/bash
if [[ ! "$(/usr/sbin/service mysql status)" =~ "start/running" ]]
then
    /usr/sbin/service mysql start
fi

Be sure that is executable:

chmod +x /path/to/script

Then add a new entry in the root crontab as follow:

Edit root crontab file using:
```
sudo crontab -e
```
And add the following line to the file:
```
*/1 * * * * /path/to/script
```
Note: I have set the cron job for every minute, but you can change as you wish or as you think is better. See http://en.wikipedia.org/wiki/Cron in this sense.

edited Aug 22 '14 at 17:11

answered Apr 21 '14 at 07:40

Radu Rădeanu

169,590

I setup it as crontab, I guess problem is with the script, i'll try above script – Vaibhav Dhage Apr 21 '14 at 07:45
./mysql-check.sh: line 2: [: =~: binary operator expected error in above script – Vaibhav Dhage Apr 21 '14 at 07:48
I believe you want to negate that regex matching with ! if you actually intend to restart the mysql service on crash – Flint Apr 21 '14 at 08:01
@Flint That's true also... Sorry, I'm still drinking my morning coffee. :) – Radu Rădeanu Apr 21 '14 at 08:03
@D_Vaibhavツ Now should be everything OK. So, try now, as root. – Radu Rădeanu Apr 21 '14 at 08:06
I have added crontab as */1 * * * * /home/ubuntu/mysql-check.sh – Vaibhav Dhage Apr 21 '14 at 08:55
I had to add @donkzilla PATH value to my crontab in order for it to work. – emeraldjava Oct 27 '15 at 16:07
I added echo "MySQL restarted" | mail -s "vvaaccc.com MySQL" testtt@gmail.com to get notified each time restart the mysql, each time I run the bash file it is sending the mail, so I feel if condition is not checking well where there mysql is running or not, so it is restarting the service each time. – Bira Nov 05 '18 at 08:46
#!/bin/bash TMP=mysqladmin -u root -pPassword status 2>&1 | head -n 1 | cut -f1 -d: case ${TMP} in Uptime) echo "MySQL is running." echo "You are good" ;; *) service mysql restart # the following sends an email for notification, change email address if needed. echo "MySQL restarted" | mail -s "your-site-name.com MySQL" email@gmail.com ;; esac – Bira Nov 05 '18 at 08:57
I had to change "start/running" to "active (running)" and then it worked – omega1 Feb 28 '19 at 10:56

score 3 · Answer 2 · answered Aug 22 '14 at 16:14

3

Radu's answer nearly worked. I had to set the path to make it work:

#!/bin/bash
PATH=/usr/sbin:/usr/bin:/sbin:/bin
if [[ ! "$(service mysql status)" =~ "start/running" ]]
then
    service mysql start
fi

answered Aug 22 '14 at 16:14

Donkzilla

31

1

In fact I have set my PATH in the crontab file. Anyway, in your case you need to use PATH=/usr/sbin:$PATH or use the full path for service as I edited my answer. – Radu Rădeanu Aug 22 '14 at 17:15

Pablo Bianchi · Answer 3 · 2023-02-24T04:44:24.267

Restart

With systemd you can set up your service to Restart on certain conditions:

systemctl cat mysql.service | grep Restart     # Check current status. cat PATTERN... Show files and drop-ins of specified units

Probably you wish to move from on-abort to on-failure, on [Service] section.

sudo EDITOR=nano systemctl edit mysql.service

nano or whatever editor you want.
To do this temporary use --runtime, changes will be lost on next reboot.
Add a RestartSec= to sleep before restarting a service.

Other useful commands:

sudo systemctl daemon-reload  # Reload systemd manager configuration. `systemctl edit` automatically does this for you.
systemctl cat mysql.service   # unit configuration
systemd-delta                 # Check the whole system changes

OOMScoreAdjust

On the same place, you may also want to adjust systemd OOMScoreAdjust:

Sets the adjustment value for the Linux kernel's Out-Of-Memory (OOM) killer score for executed processes. Takes an integer between -1000 (to disable OOM killing of processes of this unit) and 1000 (to make killing of processes of this unit under memory pressure very likely).

# Useful options not previously available in [mysqld_safe]
Kernels like killing mysqld when out of memory because its big.
Lets temper that preference a little.
OOMScoreAdjust=-600

Shell script issue: cron job script to Restart MySQL server when it stops accidentally

4 Answers4

Restart

OOMScoreAdjust

Kernels like killing mysqld when out of memory because its big.

Lets temper that preference a little.

OOMScoreAdjust=-600