Logrotate

Logrotate is a utility that rotates logs. Log rotation simply means to rename an existing log file to something else, thereby keeping the log file sizes tenable. Logrotate makes it easy to define log rotation rules, such as how many old logs to keep and for how long, the size a log should be before it's rotated, any post-rotation commands it needs to run, and more.

Introduction

Logrotate is typically found in your distro's repos as 'logrotate'.

# yum -y install logrotate

Logrotate is triggered daily via a cronjob and as a result, there is no logrotate daemon. Typically, the cronjob is installed in /etc/cron.daily/ but could also be as a @daily job in /etc/crontab on some systems.

By default, installing Logrotate will also include some standard configuration files that will rotate some common system logs in /var/log.

Configuration

Configuration is done with /etc/logrotate.conf and additional log rotate definitions can be placed in /etc/logrotate.d/. For example, we could put httpd log rotation rules in /etc/logrotate.d/httpd.

Log rotations are defined with the following syntax:

/path/to/logs/*.log {
 ** Directives **
}

It should also have at minimum the following directives:

Description	Directives
When to rotate. By time or by size.	daily, weekly, monthly OR size based: size 10M
How many rotated logs to keep. Eg. keep 30 logs. Anything past this will be deleted. Set this to 0 to delete all rotated logs.	rotate 30

You may also optionally add the following directives depending on your needs:

Description	Directives
Whether to create a new empty log after rotation is done. Optionally, you may specify the new file's mode and ownership.	create, create mode owner group, nocreate
Use date as the suffix for rotated logs using the specified date format. Creates logs like 'messages-2020-12-26'	dateext dateformat .%Y-%m-%d
If you are not using date extensions, logrotate will use numbers starting at 0 instead. Specify the starting number. Eg. 1. The first rotated log would be 'messages.0'.	start 1
Whether to compress the log or not. Uses gzip by default.	compress
The extension of rotated log files. Eg. 'messages-2020-12-26.log' or 'messages.0.log'.	extension log
Send an email when a log is rotated out of existance.	mail user@domain.com
Move rotated logs to a different location.	olddir /var/log/rotated
Ignore if file is missing	missingok
Don't rotate if the file is empty	notifempty
Run a command after the rotation is executed. The contents are run using /bin/sh. The log files are passed as an argument.	postrotate /bin/kill -HUP endscript

After defining your new rule, you can test it by running logrotate -v /etc/logrotate.d/your-new-config. If your logs aren't rotating, it's possible you need to tweak the state file in /var/lib/logrotate/logrotate.status for your particular log file in order for the rotate conditions to be fulfilled.

Tasks

Rotating Traefik access logs

After configuring Traefik to log to /var/log/traefik, you may want to use this rule to rotate logs and then send USR1 to the container running Traefik.

/var/log/traefik/access.log {
  monthly
  rotate 60

  create 0644 root root
  missingok
  notifempty
  compress
  dateext
  dateformat .%Y-%m-%d

  postrotate
    docker kill --signal="USR1" $(docker ps | grep traefik | awk '{print $1}')
  endscript
}

See also

• https://linux.die.net/man/8/logrotate