Monit: Monitor BIND 9 (named) Name Server and Auto Restart SSH If It Does Not Respond

To use Monit to monitor the BIND 9 (named) name server and automatically restart it if it does not respond, you will need to add a configuration file to the /etc/monit/conf.d/ directory.

Here's an example of a Monit configuration file that you can use to monitor the BIND 9 name server and restart it if it does not respond:

check process named with pidfile /var/run/named/named.pid
  start program = "/usr/sbin/service bind9 start"
  stop program = "/usr/sbin/service bind9 stop"
  if failed host 127.0.0.1 port 53 protocol dns then restart
  if 5 restarts within 5 cycles then timeout

This configuration file tells Monit to monitor the BIND 9 process using the PID file at /var/run/named/named.pid. If the process is not running, Monit will start it using the /usr/sbin/service bind9 start command. If the process is running but does not respond to DNS queries on port 53, Monit will restart it. If the process is restarted 5 times within 5 cycles, Monit will consider it to be in a failed state and will not attempt to restart it again.

To monitor SSH and automatically restart it if it does not respond, you can use a similar configuration file. Here's an example:

check process ssh with pidfile /var/run/sshd.pid
  start program = "/usr/sbin/service ssh start"
  stop program = "/usr/sbin/service ssh stop"
  if failed host localhost port 22 protocol ssh then restart
  if 5 restarts within 5 cycles then timeout

This configuration file tells Monit to monitor the SSH process using the PID file at /var/run/sshd.pid. If the process is not running, Monit will start it using the /usr/sbin/service ssh start command. If the process is running but does not respond to SSH connections on port 22, Monit will restart it. If the process is restarted 5 times within 5 cycles, Monit will consider it to be in a failed state and will not attempt to restart it again.

After you have created the Monit configuration files, you will need to restart Monit to apply the changes. You can do this by running the following command:

systemctl restart monit

Monit will now monitor the BIND 9 name server and SSH and automatically restart them if they do not respond. You can use the monit command to check the status of the monitored services and to view any log messages or alerts that Monit generates.