Nagios Support Forum

No easy way, but you can tell check_by_ssh to login with nagios or root or whatever on the remote system by using the -l argument.

does this look correct ?

/usr/local/nagios/libexec/check_by_ssh -H $HOST -C "top -cSbn 1" -l nagios

Assuming you have apache's id_rsa.pub from your nagios box in ~/.ssh/authorized_keys for nagios user on the remote box - yes