Monitor ssh on non-default port with Nagios

In ssh pluging config /usr/local/nagios/etc/objects/commands.cfg, there an alias named check_ssh_port.
if it not existe you may define it like above:

define command{ command_name check_ssh_port command_line $USER1$/check_ssh  -p $ARG1$ $HOSTADDRESS$ }

in the service file /usr/local/nagios/etc/servers/hosttomonitor.cfg, define you ssh service to monitor like this:

define host{ use                                 linux-server host_name                           hosttomonitor.localnet alias                               hosttomonitor address                             10.10.10.19 max_check_attempts                  5 check_period                        24x7 notification_interval               30 notification_period                 24x7 } define service {         use                         generic-service         host_name                   hosttomonitor.localnet         service_description         SSH2         check_command               check_ssh_port!1422         notifications_enabled       0         }

replace 1422 by you default ssh port and server by your target.

finally restart nagios service