I added a new check command to nagios to check the sendmail mail queue but received an error while executing within nagios:

/usr/bin/mailq = can not chdir(/var/spool/mqueue/): Permission denied
Program mode requires special privileges, e.g., root or TrustedUser.
CRITICAL: Error code 78 returned from /usr/bin/mailq

This is because the nagios process (which runs as the nagios user) does not have the permissions to look at the spool directory for mail (/var/spool/mqueue) – the permissions on that directory are 700 and owned by root.

The fix is to permit nagios to execute this command as root and also to run the /usr/bin/mailq program with sudo in the check_mailq perl script.

Step 1: Modify check_mailq
Edit the check_mailq file, after making a backup of the file. Search for the place where the mailq is opened for reading from the pipe and add /usr/bin/sudo prior to the command. The resulting line looks like the following (note: this is does using sendmail as the MTA):

if (! open (MAILQ, "/usr/bin/sudo $utils::PATH_TO_MAILQ | " ) ) {

Step 2: Modify sudoers
Edit the sudoers file to give nagios permission to execute /usr/bin/mailq as root without requiring a password. I accomplished this by adding the following line to the end of the file:

nagios ALL= (root) NOPASSWD: /usr/bin/mailq


Test prior to reloading nagios by executing the check_mailq command as nagios:

su nagios -c "./check_mailq -w 5 -c 10"

If you see an error message about a tty, like:

sudo: sorry, you must have a tty to run sudo

or in nagios:

CRITICAL: Error code 1 returned from /usr/bin/mailq

you will need to either comment out the line about requiring the tty (Defaults requiretty), or add a new line not requiring the tty for nagios:

Defaults:nagios !requiretty


Ever since upgrading to Snow Leopard, my MacBook Pro often was unable to see the local network hosts. It turns out the mDNSResponder, now responsible for DNS caching, is rotating the order of the DNS Servers. Since I have my own DNS server that is the authority for my network, this should always be the first one checked. As it is also a home network, it made sense to have a backup DNS server pushed out via DHCP. However, it turns out that having the backup DNS server (my favorite: OpenDNS) in case the local one fails, actually causes the problem on the Snow Leopard machines.

I found a great amount of information regarding this at the Apple Support Discussions list. If this issue plagues you, many of the messages in this thread are a worthwhile read.

The following is useful when the linux machine is not correctly joined to a domain:

I have noticed a number of PROBLEM alerts from my Nagios 3.2.0 implementation on Fedora 12 when checking the available disk space on a WinXP share such as:

• Result from smbclient not suitable
• No Answer from Client

This used to work before upgrading both my Nagios and Fedora implementations.

To get this working once again, I’ve had to do two things – allow Nagios to login and specify the domain name as part of the user name on the check_disk_smb command.

To permit login to nagios, edit the passwd file with sudo vipw and change the shell to /bin/sh for nagios (should have been /sbin/nologin).

Next, in the private configuration file for Nagios, change the USER variable to be DOMAIN\\\\User; note the four backslashes are necessary. If that USER variable is being used elsewhere where the the new value would alter the results from other Nagios checks, add a new USER variable and update the configuration files accordingly.