Nagios Support Forum

The nsclient password in XI is typically defined in resources.cfg. It needs to match the password probably defined in nsclient.ini if I recall.

If you can't be root you need to turn this over to someone who can be root. Otherwise this is pointless.
This is basic linux administration.
When someone with root access and admin experience can respond a meaningful reply might be forthcoming.

The root user is the root user. It's called root.
whoami

Are you the root user?
cd /tmp
du -sk ./* | sort -rn

I think it's time to go into /tmp as root and use du to find what's using space.

Maybe try searching the internet on those file names.

sort: cannot create temporary file in '/tmp': No space left on device
ls -l /tmp
What files are there filling the FS?

Filling up a filespace isn't really a nagios issue and the following message isn't very hard to understand.
sort: cannot create temporary file in '/tmp': No space left on device

If you can ping the host and the port is open you have an odbc connection issue. Often a uname/pasword issue.

Delete the .rrd and .xml measurement files.