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Running Linux, Fourth Edition by Lar Kaufman, Terry Dawson, Matthias Kalle Dalheimer, Matt Welsh

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Managing System Logs

The syslogd utility logs various kinds of system activity, such as debugging output from sendmail and warnings printed by the kernel. syslogd runs as a daemon and is usually started in one of the rc files at boot time.

The file /etc/syslog.conf is used to control where syslogd records information. Such a file might look like the following (even though they tend to be much more complicated on most systems):

*.info;*.notice    /var/log/messages 
mail.debug         /var/log/maillog 
*.warn             /var/log/syslog 
kern.emerg         /dev/console

The first field of each line lists the kinds of messages that should be logged, and the second field lists the location where they should be logged. The first field is of the format:

            facility.level [; facility.level ... ]

where facility is the system application or facility generating the message, and level is the severity of the message.

For example, facility can be mail (for the mail daemon), kern (for the kernel), user (for user programs), or auth (for authentication programs such as login or su). An asterisk in this field specifies all facilities.

level can be (in increasing severity): debug, info, notice, warning, err, crit, alert, or emerg.

In the previous /etc/syslog.conf, we see that all messages of severity info and notice are logged to /var/log/messages, all debug messages from the mail daemon are logged to /var/log/maillog, and all warn messages are logged to /var/log/syslog. Also, any emerg warnings from the kernel are sent to the console ...

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