This documentation is for the extended support release (ESR) version of Cumulus Linux. We will continue to keep this content up to date until 21 February, 2023, when ESR support ends. For more information about ESR, please read this knowledge base article.

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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 Spectrum 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/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.

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/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.

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/fsck/*

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

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/installer/*

Directory containing files related to the installation of Cumulus Linux.

/var/log/lastlog

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

/var/log/netd.log

Log file for NCLU.

/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/frr/*

Logs for FRRouting.

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

/var/log/rdnbrd.log

Logs for redistribute neighbor.

/var/log/snapper.log

Log file for snapshots.

These logs are valuable for the snapshots you take on your switch.

/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/wtmp

Login records file.