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Troubleshooting Log Files

The only real unique entity for logging on Cumulus Linux compared to any other Linux distribution is switchd.log, which logs the HAL (hardware abstraction layer) from hardware like the Broadcom or Mellanox ASIC.

This guide on NixCraft is amazing for understanding how /var/log works. The green highlighted rows below are the most important logs and usually looked at first when debugging.

Log

Description

Why is this important?

/var/log/alternatives.log

Information from the update-alternatives are logged into this log file.

/var/log/apt

Information the apt utility can send logs here; for example, from apt-get install and apt-get remove.

/var/log/audit/*

Contains log information stored by the Linux audit daemon, auditd.

/var/log/auth.log

Authentication logs.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/autoprovision

Logs output generated by running the zero touch provisioning script.

/var/log/boot.log

Contains information that is logged when the system boots.

/var/log/btmp

This file contains information about failed login attempts. Use the last command to view the btmp file. For example:

cumulus@switch:~$ last -f /var/log/btmp | more

/var/log/clagd.log

Logs status of the clagd service.

/var/log/cron.log

Log file for cron jobs.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/daemon.log

Contains information logged by the various background daemons that run on the system.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/debug

Debugging information.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/dmesg

Contains kernel ring buffer information. When the system boots up, it prints number of messages on the screen that display information about the hardware devices that the kernel detects during boot process. These messages are available in the kernel ring buffer and whenever a new message arrives, the old message gets overwritten. You can also view the content of this file using the dmesg command.

dmesg is one of the few places to determine hardware errors.

/var/log/dpkg.log

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

/var/log/faillog

Contains failed user login attempts. Use the faillog command to display the contents of this file.

/var/log/fsck/*

The fsck utility is used to check and optionally repair one or more Linux filesystems.

/var/log/kern.log

Logs produced by the kernel and handled by syslog.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/lastlog

Formats and prints the contents of the last login log file.

/var/log/lpr.log

Printer logs.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/mail.log

Mail server logs. Also includes mail.err, mail.info and mail.warn.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/messages

General messages and system-related information.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/news/*

The news command keeps you informed of news concerning the system.

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/ntpstats

Logs for network configuration protocol.

/var/log/openvswitch/*

ovsdb-server logs.

/var/log/quagga/*

Where Quagga logs to once enabled.

This is how Cumulus Networks troubleshoots routing. For example an md5 or mtu mismatch with OSPF.

/var/log/switchd.log

The HAL log for Cumulus Linux.

This is specific to Cumulus Linux. Any switchd crashes are logged here.

/var/log/syslog

The main system log, which logs everything except auth-related messages.

The primary log; it's easiest to grep this file to see what occurred during a problem.

/var/log/user.log

Note that Cumulus Linux does not write to this log file; but because it's a standard file, Cumulus Linux creates it as a zero length file.

/var/log/watchdog

Hardware watchdog log files.

/var/log/wtmp

Login records file.