Monitoring the servers could be well – “not difficult” but boring and monotonous. And since this is something that you should ideally do on daily basis, so why not have a script for the same.
You can’t possibly copy your ssh-keys to all the servers that you are monitoring, better if you can, then you need to do ssh to server with password. So, here is link to my github repo for monitoring servers with perl script. Preety straight forward script and you can schedule this in cron to get a daily mail.
The script covers solaris and Linux ( i.e. Ubuntu/Fedora/Debian/ideally any distro)
Do let me know in comments, if you feel something is missnig.