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7.5.1. Monitoring Logs with logcheck

The logcheck program monitors log files every hour by default and sends unusual log messages in emails to the administrator for further analysis.

The list of monitored files is stored in /etc/logcheck/logcheck.logfiles. The default values work fine if the /etc/rsyslog.conf file has not been completely overhauled.

logcheck can report in various levels of detail: paranoid, server, and workstation. paranoid is very verbose and should probably be restricted to specific servers such as firewalls. server is the default mode and is recommended for most servers. workstation is obviously designed for workstations and is extremely terse, filtering out more messages than the other options.

In all three cases, logcheck should probably be customized to exclude some extra messages (de- pending on installed services), unless you really want to receive hourly batches of long unin- teresting emails. Since the message selection mechanism is rather complex, /usr/share/doc/ logcheck-database/README.logcheck-database.gz is a required—if challenging—read.

The applied rules can be split into several types:

• those that qualify a message as a cracking attempt (stored in a file in the /etc/logcheck/ cracking.d/ directory);

• ignored cracking attempts (/etc/logcheck/cracking.ignore.d/);

• those classifying a message as a security alert (/etc/logcheck/violations.d/);

• ignored security alerts (/etc/logcheck/violations.ignore.d/);

• finally, those applying to the remaining messages (considered as system events).

ignore.d files are used to (obviously) ignore messages. For example, a message tagged as a cracking attempt or a security alert (following a rule stored in a /etc/logcheck/violations.d/myfile file) can only be ignored by a rule in a /etc/logcheck/violations.ignore.d/myfile or /etc/ logcheck/violations.ignore.d/myfile-extension file.

A system event is always signaled unless a rule in one of the /etc/logcheck/ignore.d.

{paranoid,server,workstation}/ directories states the event should be ignored. Of course, the only directories taken into account are those corresponding to verbosity levels equal or greater than the selected operation mode.

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