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exim4 Issues - a Review of /var/log/exim4/paniclog

exim4 is a Mail Transfer Agent (MTA), but as configured on my RPi, it cannot send or receive mail from the Internet. It is passed down to RPi from Debian, and was installed on my system as a "Suggested Package" when I installed at. It may be used on the RPi primarily as a means for service daemons (e.g. using the MAILTO variable in cron) to communicate issues to the administrator. For that reason alone, it should be maintained.

It seems there is a problem with the default exim4 configuration for RPi. If you rummage about in the log files occasionally as I do, you may have noticed several files in/var/log : mail.warn, mail.info, mail.err, mail.log, syslog and daemon.log containing the following ALERT:

exim4: ALERT: exim paniclog /var/log/exim4/paniclog has non-zero size, mail system possibly broken

Following up, you may see the following error message in /var/log/exim4/paniclog:

socket bind() to port 25 for address ::1 failed: Cannot assign requested address: daemon abandoned

Note that address ::1 is the IPv6 loopback address; equivalent (roughly) to 127.0.0.1 in IPv4.

You will also note that the exim4 daemon is not running;

$ pgrep exim 
$

I think this is a bug - an issue with the default configuration files installed with exim4. Here's what I did to address that:

1. Edit the exim4 configuration file as follows:

$ sudo nano /etc/exim4/update-exim4.conf.conf

Edit this line:

FROM: dc_local_interfaces='127.0.0.1 ; ::1'
  TO: dc_local_interfaces='127.0.0.1'

Save & exit the editor, apply the update & re-start exim4:

$ sudo update-exim4.conf
$ sudo systemctl restart exim4

Other solutions advised adding the following line to the configuration file, but I found this unnecessary.

disable_ipv6='true'

2. Verify /etc/sysctl.conf contains the following line:

net.ipv6.conf.all.disable_ipv6 = 1

Other solutions also advised adding this line, but it was included in my default conf file.

3. OPTIONAL: Clear the logs

Clearing /var/log/exim4/paniclog will stop recurring "false alarm" log entries in, e.g. /var/log/mail.warn:

$ sudo truncate -s 0 /var/log/exim4/paniclog

REFERENCES:

  1. exim4 won't bind to port 25
  2. exim in the Debian wiki
  3. An Internet search on exim
  4. Crontab Email Settings ( MAILTO )