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Rsyslog property based filtering features

By Emanuele “Lele” Calò
September 4, 2014

Do you need something more powerful than the usual, clunky selectors based Rsyslog filtering rules but still you don’t see the benefit of going full throttle and use RainerScript?

Perhaps you weren’t aware, but there is an additional filtering rule you may not have used, which is a great alternative to the classic selector-based one, called property-based filtering.

This kind of filtering lets you create rules like:

:msg, contains, "firewall: IN=" -/var/log/firewall

There’s a few more properties that you can use like hostname,fromhost,fromip and the number (and variety) is growing over time.

Instead of just verifying that a specific string is contained in the highlighted property, you could also be interested in operators like isempty, isequal or the powerful regex and ereregex which could be used to compare the string content against regexes, that we all love so much.

:fromhost, regex, ".*app-fe\d{2}" -/data/myapp/frontend_servers.log
:fromhost, regex, ".*app-db\d{2}" -/data/myapp/DB_servers.log

Also remember that you can always use the ! to negate the condition and the discard operator to block Rsyslog from further rules parsing for that specific content:

:msg, !contains, "firewall: IN=" -/data/myapp/all_logs_but_firewall_related.log
:fromhost, regex, ".*appfe\d{2}" ~ -/data/myapp/frontend_servers.log
:fromhost, regex, ".*appdb\d{2}" ~ -/data/myapp/DB_servers.log
*.* /data/myapp/all_logs_but_firewall_related_and_not_from_appfe_and_appdb_servers.log

In case you don’t know what the - (dash) sign stands for, that’s used to put the log writing process in async mode, so that Rsyslog can proceed with other filtering and won’t wait for disk I/O to confirm a successful write before proceeding to something else.

Now go back to your logging system and let us know what nice set up you came up with!


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