Unison File Synchronizer is a tremendous utility. It keeps the contents of two directories in sync with one another. It’s fast, secure, lightweight and good at sorting out collisions but unfortunately it lacks the ability to generate alerts when errors occur. Instead it just silently makes note of the error in a log file.

Luckily we can watch Unison’s logs for error events and notify ourselves as soon as a match is found with a tool called Simple Event Correlator, or SEC.

By default, Unison writes log entries in a file named “unison.log” under the home directory of the user running the application. We’ll assume that unison is running as root and is logging to the default location of /root/unison.log.

To configure SEC we simply need to write a short rule that includes the regular expression that matches a unison error message and the action we wish to execute when a match is found. Here is a simple example rule to send e-mail alerts on unison file conflicts.

type=Single
ptype=RegExp
pattern=(^\[CONFLICT\]|^Fatal error)
desc=$0
action=pipe '' /usr/bin/tac /root/unison.log | grep '^UNISON' -m 1 -B 9999 | tac | /usr/bin/mailx -s "UNISON: $0" root

This will send an e-mail alert to root when a line starting with [CONFLICT] or Fatal Error is logged and include the most recent unison run log output in the body of the message.

To invoke sec use something to the effect of:

 sec -conf=./sec_unison.conf -input=/root/unison.log

Where -conf is the file containing of the above rule and -input is unison’s log file.

[ad]