Linux log files

This article identifies what is in each of the Linux® logs, where they are stored, and which distributions (distro) use the logs.

For most of the following logs, you can use vi, less, tail, or cat to view the log details. Exceptions to this rule are noted in the descriptions.

• /var/log/alternatives.log (Ubuntu® operating system/Debian® (DEB))

  Stores information from update-alternatives.

• /var/log/apache2/access.log (Ubuntu operating system/DEB)

  Stores requests, such as HTTP GET and POST requests, that are processed by Apache®. Parse these logs by using log parsers such as awstats or webalizer. Configure this log by using the CustomLog directive.

• /var/log/apache2/error.log (Ubuntu operating system/DEB)

  Stores all Apache errors and diagnostic information found while serving requests. The location of the error.log file is set by the ErrorLog directive.

• /var/log/audit/audit.log

  Stores information from the Linux audit daemon (auditd). This log contains information about the files on which users perform reads or writes. For example, you can use this log to determine who changed a specific file.

• /var/log/auth.log

  Contains system authorization information, including user logins and which authentication mechanism was used.

• /var/log/boot

  Contains information about the boot process after the kernel is loaded. Information includes things such as system file checks, mounting a file system, starting a firewall, starting network devices, and starting services.

• /var/log/btmp

  Contains failed login attempts. Use the last command to view this log. For example: last -f /var/log/btmp |more

• /var/log/cron

  Stores information from crondaemon and anacron after they start a cron job.

• /var/log/dmesg

  Contains kernel information about hardware and devices detected during the boot process. This file is overwritten when new messages are sent to it, such as during the next boot.

• /var/log/dpkg.log (Ubuntu operating system/DEB)

  Stores information that is logged when a package is installed or removed by using the dpkg command.

• /var/log/faillog

  Contains failed user login attempts. Use faillog to access the information.

• /var/log/kern.log (Ubuntu operating system/DEB, and can be configured for Centos® and Red Hat®)

  Contains log details from the kernel’s initialization at system bootup, as well as any kernel errors or informational messages that are sent from the kernel.

• /var/log/lastlog

  Displays recent login information. Run this command to view the log entries.

• /var/log/maillog.log (Centos/Red Hat)

  Stores information from the mail server that is running on your system, such as Sendmail® logging information.

• /var/log/mail.log (Ubuntu operating system/DEB)

  Stores information from the mail server that is running on your system, similar to maillog.log for the Centos and Red Hat flavors.

• /var/log/mail

  Contains additional logs provided by your mail server. For example: Sendmail stores collected mail statistics in /var/log/mail/statistics.

• /var/log/messages (Centos/Red Hat)

  Contains global system messages, including the messages logged during boot. Log entries include information from mail, cron, daemon, kern, auth, and so on.

• /var/log/sa

  Contains daily sar files collected by the sysstat package.

• /var/log/samba/

  Contains log information stored by the samba daemon, which is used to connect to Microsoft® Windows® and Linux file systems.

• /var/log/setroubleshoot/

  Used by SELinux to capture security issues in files and log that information.

• /var/log/secure (Centos/Red Hat)

  Stores information related to authentication and authorization privileges. For example, sshd logs all information here, including unsuccessful attempts.

• var/log/wtmp or /var/log/utmp

  Contains login records and shows who is logged into the system. The who command uses this file to display the information.

• /var/log/yum.log (Centos/Red Hat)

  Stores information that is logged when a package is installed or removed.