Rsyslog

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Revision as of 23:12, 4 September 2014 by Deoren (talk | contribs) (Added more references, basic overview and slight header level adjustment.)

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Overview

From the rsyslog homepage:

Rsyslog is a rocket-fast system for log processing. It offers high-performance, great security features and a modular design. While it started as a regular syslogd, rsyslog has evolved into a kind of swiss army knife of logging, being able to

accept inputs from a wide variety of sources, transform them, and output the results to diverse destinations.

Rsyslog has a strong enterprise focus but also scales down to small systems. It supports, among others, MySQL, PostgreSQL, failover log destinations, syslog/tcp transport, fine grain output format control, high precision timestamps, queued operations and the ability to filter on any message part.


discard operator

The discard operator (aka, "discard action" operator) is the ~ character. Using it tells rsyslog that you want to discard log messages matched by filters. I often see that operator in conjunction with the & character and allows for having multiple actions per selector. This allows for combinations where you direct matching log messages to a specific file and preventing the same message from being logged a second time.


v5-stable

From an Ubuntu 12.04 LTS box:

# /etc/rsyslog.d/20-ufw.conf

# Log kernel generated UFW log messages to file
:msg,contains,"[UFW " /var/log/ufw.log

# Uncomment the following to stop logging anything that matches the last rule.
# Doing this will stop logging kernel generated UFW log messages to the file
# normally containing kern.* messages (eg, /var/log/kern.log)
& ~


v7-stable

As of v7-stable this operator has been marked as deprecated and a different syntax is suggested as this warning suggests:

 rsyslogd-2307: warning: ~ action is deprecated, consider using the 'stop' statement instead [try http://www.rsyslog.com/e/2307 ]

From an Ubuntu 14.04 LTS box that runs v7.4.x and the suggested syntax:

# /etc/rsyslog.d/20-ufw.conf

:msg,contains,"[UFW " /var/log/ufw.log

# Uncomment the following to stop logging anything that matches the last rule.
# Doing this will stop logging kernel generated UFW log messages to the file
# normally containing kern.* messages (eg, /var/log/kern.log)
& stop

The & character is necessary (I found out the hard way) to "glue" the discard action to the filter above, otherwise it stops all log messages from being logged from that point forward.

Another example using a newer syntax:

auth,authpriv.* {
 /var/log/secure
 stop
}


References

Rsyslog actions

Filters

Regular Expressions

Properties

Receiving from and Sending to remote Syslog boxes