Wednesday, January 27, 2010

Ubuntu Log Files

An important part of Ubuntu system administration is knowing what’s happening on the
system. Because there’s so much activity happening behind the scenes, it’s often hard
to keep tabs on your workstation. Fortunately, Ubuntu provides a relatively easy way for
you to look at what’s happening on the system. This section walks through the use of log
files and explains how to easily view them all from one location.

Ubuntu Log Files
Ubuntu provides several levels of log files for the system. Log files are used by processes
to track errors, warnings, and general items of information that may be important. It’s
usually a good idea to take a peek at the log files on a regular basis to see what’s happening
on the system.

The process that controls logging on the Ubuntu system is syslogd. The syslogd process
runs in the background and directs log messages from applications and the Linux kernel
to different log files. Because there’s so much activity going on, Ubuntu uses several
different log files to track different features of the system. All of the log files are stored
in the /var/log directory on the Ubuntu system.

The Ubuntu Log Files
auth.log System authentication events, such as login attempts

daemon.log Background process events

kern.log Linux kernel events

messages Standard system and application events

syslog System errors

user.log User events

Xorg.0.log X Window system events

Fortunately, you don’t have to hunt for each of these log files individually. Ubuntu provides a handy utility that helps manage all of the log files from a single graphical interface.

The System Log Viewer
The System Log Viewer is a utility in the Administration menu (select System ->
Administration -> System Log from the Panel menu). It allows you to quickly view all of the configured log files from a single location. The System Log Viewer window has three sections:

• The log file list: Lists the log files available to view. Log files with data that have been added since the System Log Viewer was started appear in bold.

• The calendar: Allows you to select a day from the log files to view. Ubuntu creates a new version of each log file each day. You can view any of the available daily log files by selecting the date in the calendar. Days with available log files appear in bold.

• The log viewer: Displays the contents of the selected log file.

The System Log Viewer uses monitored mode to watch the log files in real-time. This mode notifies you of new log file entries by displaying the log filename in bold in the log file list and making the new entries appear in bold in the log viewer. If your system is experiencing a problem that is quickly filling up the log file, you can disable monitored mode by selecting View -> Monitor from the menu bar.

The log files used by the syslogd process are defined in the /etc/syslog.conf file. This file defines what type of log entries are stored in which log files.

Log entries are classified by a tiered system, from lowest to highest priority:
• debug: application debugging messages
• info: informational messages
• notice: event notices from applications
• warning: minor error messages
• err: an error condition in an application
• crit: a critical system error
• alert: a system error that requires immediate action
• emerg: an error that prevents the system from running

Some Linux distributions provide a single log file for handling critical and alert messages, but Ubuntu doesn’t use this technique. Instead, it separates log messages by source and importance.

For example, you’ll find four log files for logging mail activity on the Ubuntu system: mail.error,, mail.log, and mail.warn. Each log file contains messages for the specified log level for the mail system.

Source of Information : Wiley Ubuntu Linux Secrets

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