View source for How To Manage Logfiles with Logrotate

[[Category:Ubuntu]]
[[Category:Ubuntu System]]
[[Category:201904]]

= See also: Systemd logging =

Systemd logging aims to be better than syslog. Usually both Systemd and Syslog are available on the system. You might consider looking into it:
* https://www.loggly.com/ultimate-guide/linux-logging-with-systemd/

Sent log message from shell script:
<source lang=bash>
#-p [severity 0-7] 0=emergency, 2=error, 6=info, 7=debug
echo "[wjv backup] backup error message" | systemd-cat -t "identifier" -p 2
</source>

= Syslog =

<!-- retention rotate logging -->
To prevent your log files from growing without limit the 'logrotate' command can be used to specify what you want to keep. There are a lot of options and you might want to integrate your log-cleaning into the daily logrotate schedule. 

More info here:
* https://www.digitalocean.com/community/tutorials/how-to-manage-logfiles-with-logrotate-on-ubuntu-16-04

Complete info can be found on the man page:
<source lang=bash>
man logrotate
</source>

= Independent configuration  =

This example is limited to an independent configuration and some basic options. 

Create logrotate config file:

<syntaxhighlight lang=bash>
sudo nano /home/user1/logs/example.conf
</syntaxhighlight>

<blockquote>
<syntaxhighlight lang=bash>
/home/user1/logs/*.log {
    rotate 4
    daily
    size 10k
    create
    compress
    delaycompress
}
</syntaxhighlight>
</blockquote>

This file will be ignored if it hasn't the correct permissions. Permissions that work are 'all=read' (444) OR 'user/owner=read/write, group and other=read' (644):

<syntaxhighlight lang=bash>
chmod u=rw,g=r,o=r /home/user1/logs/example.conf
</syntaxhighlight>

Options explained:

{| class="wikitable"
|-
! Option !! Meaning
|-
| rotate 4 || Keep 4 archived logfiles (1-4), older files are disposed of
|-
| daily || Rotate not more than once a day, the state-file is used to check if the logfile was rotated earlier today.
|-
| size 1k || Do not rotate if the logfile size is less than 1k
|-
| missingok || Do not report an error if the logfile does not exist
|-
| compress || Compress (gz) rotated logfiles
|-
| delaycompress || Compress the last archived logfile with the next rotation (2-4 will be compressed)
|-
| notifempty || Do not rotate if the logfile is empty
|-
| create || Create new empty logfile after rotation
|}

== Manually logrotate ==

Option -v (verbose) is added so you can see what is happening.

<syntaxhighlight lang=bash>
logrotate -v /home/user1/logs/example.conf --state /home/user1/logs/logrotate-state
</syntaxhighlight>

== Add to daily crontab ==

The time that was used here is daily at 4:04 am.

<syntaxhighlight lang=bash>
nano /etc/crontab
</syntaxhighlight>

  04 04 * * * *  /usr/sbin/logrotate /home/user1/logs/example.conf --state /home/user1/logs/logrotate-state

= System settings and locations for logrotate =

Linux allows you to use the general logging and logrotate process. It will help if you use the standard files and locations to reduce the complexity of your app. 

Start-off with placing your app-logs in your own app directory under /var/log/

<syntaxhighlight lang=bash>
mkdir /var/log/yourapp
</syntaxhighlight>

A logfile could be '''/var/log/yourapp/yourapp.log'''

Sytem logrotate default settings can be found in the file '''/etc/logrotate.conf''' you don't have to edit this file. The file '''/etc/logrotate.conf''' will include all configuration files in the directory '''/etc/logrotate.d/'''. You should place 'yourapp' logrotate configuration in that directory in a new file.

<syntaxhighlight lang=bash>
nano /etc/logrotate.d/yourapp
</syntaxhighlight>

<blockquote>
<syntaxhighlight lang=bash>
/var/log/yourapp/*.log {
    daily
    missingok
    rotate 7
}
</syntaxhighlight>
</blockquote>

Rotating will not be done more that once a day as it will be part of a daily crontab job. The log status for all the logs (name,date and time) will be kept in a single file:

<syntaxhighlight lang=bash>
cat /var/lib/logrotate/status
</syntaxhighlight>

= Empty a logfile as admin =

<!-- used for log backup monitor redirect stdout -->

Clear:

<syntaxhighlight lang=bash>
echo "" | sudo tee /var/log/logfile.log
cat /var/log/logfile.log
</syntaxhighlight>

Append (-a):

<syntaxhighlight lang=bash>
echo "append this line" | sudo tee -a /var/log/logfile.log
</syntaxhighlight>