Sam Pointer

If you install the default ‘nagios3’ package from the repositories on a Debian-based distribution, you wind up with a full copy of postfix installed. This is fine if you’re simply trying to get the thing to work, but as part of a wider infrastructure you most likely do not want a full-fledged MTA arbitrarily popping up on your Nagios host - an MTA that you have to administer, monitor (!), patch and most importantly secure.

The dependency  chain that causes postfix to be installed is:

nagios3 → nagios3-core → nagios3-common → bsd-mailx → default-mta | mail-transport-agent.

Why the package maintainers made bsd-mailx dependent on a fully-fledged MTA I will never know. Perhaps they wanted to ensure things “just worked”? It still seems a bit heavy handed to me, especially when one can configure .mailrc to point to a mailhost and be done with it.

In order to install nagios3 from the repositories and satisfy those dependencies without pulling in postfix you should install the ‘lsb-invalid-mta’ package, which provides ‘mail-transport-agent’ and satisfies the dependency chain above, in place of postfix. The package provides a sendmail binary that does nothing but return a non-zero return code, so you’ll never accidentally send mail from a local system, but you will have to configure your system to take advantage of a suitable MTA host.

Here is some puppet to install nagios3 without postfix:

# /etc/puppet/modules/nagios-server/manifests/init.pp
#
# Class: nagios-server
#
# This class maintains a Nagios server.
#
# Parameters:
#       None
#
# Requires:
#       nagios-server::install
#
class nagios-server {
        include nagios-server::install

        service { 'apache2':
                ensure => running,
                enable => true,
                require => Class['nagios-server::install'],
        }

        service { 'nagios3':
                ensure => running,
                enable => true,
                require => Class['nagios-server::install'],
        }
}

# /etc/puppet/modules/nagios-server/manifests/install.pp
#
# Class: nagios-server::install
#
# This class will install a Nagios server from the repo packages
#
# Parameters:
#       None
#
# Requires:
#       Nothing
#
class nagios-server::install {

        # Prevent nagios3-common->mailx dependency from pulling in an MTA.
        package { 'lsb-invalid-mta':
                ensure => present,
        }

        $packages = ['nagios3', 'nagios-images', 'nagios-plugins', 'nagios3-doc',]
        package { $packages:
                ensure => present,
                require => Package['lsb-invalid-mta'],
        }
}

I’ve recently had cause to try to parse the output of the `mailq’ command, by dint of it being the common queue output format between sendmail and postfix, and a desire to interoperate with them both. It is a complete bastard!

Here is some to save you running the command:

-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
637F5CFF9C*    1497 Sat Dec 18 21:40:34  sender@domain.com 
                                          recepient@domain.com

4C4D5A32E6*    1481 Sat Dec 18 21:39:45  sender@domain.com 
                                         recepient@domain.com

EBBE4D5C93*    1481 Sat Dec 18 21:51:52  sender@domain.com 
                                         recepient@domain.com

 ...


36BAAA3C9E     1471 Sat Dec 18 18:19:16  sender@domain.com 
(delivery temporarily suspended: host mailxx-xx.xxxx.aol.com[xxxxxx] refused to talk to me: 421 4.7.1 : (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html)
                                         recepient@domain.com
  
350FE10A66C     1438 Wed Dec 15 01:33:38  sender@domain.com 
(lost connection with mx-c1.xxxx.net[61.20.xx.xx] while receiving the initial server greeting)
                                          recepient@domain.com

...

-- 359752 Kbytes in 174586 Requests.

This is awkward to parse because:

• The queue to which a mail identified by a given queue-id belongs to is denoted by a single character appended to the queue-id. Except if you’re in the deferred queue, in which case there is no special character - an atribute by absence, if you like.
• The ‘arrival time’ doesn’t include a year. We either have to assume that the year is the current year and open ourselves up to year-end bugs, or we have to compensate for edge cases with time and boundary checks.
• Records span multiple lines, and how many depends on the queue that the mail is in. This leads to nasty “if the last character of the first field of the following line was not an asterix of exclamation mark read two more line, otherwise read three more lines. And that field that was on the second line before is now on the third” logic in parsers.

  Whilst parsable with somewhat icky code, it just seems designed not to be parsed or piped: “records” spanning multiple lines is a definite no-no when you’re ‘xargs’-ing or piping through awk or anything else remotely UNIXy. I wonder what was going through the minds of the original authors of the `sendmail -bp` option, that `mailq` ultimately emulates?

  I’m currently working on some Ruby code to parse the output of `mailq` and to populate an ActiveRecord model with the appropriate attributes. Wrapped up as a gem, it would be a convenient way to provide Rails applications access to the mail queue.