How To Manage Logfiles with Logrotate

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:

#-p [severity 0-7] 0=emergency, 2=error, 6=info, 7=debug
echo "[wjv backup] backup error message" | systemd-cat -t "identifier" -p 2

Syslog

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:

man logrotate

Independent configuration

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

Create logrotate config file:

sudo nano /home/user1/logs/example.conf

/home/user1/logs/*.log {
    rotate 4
    daily
    size 10k
    create
    compress
    delaycompress
}

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):

chmod u=rw,g=r,o=r /home/user1/logs/example.conf

Options explained:

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.

logrotate -v /home/user1/logs/example.conf --state /home/user1/logs/logrotate-state

Add to daily crontab

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

nano /etc/crontab

 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/

sudo mkdir /var/log/yourapp

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.

sudo nano /etc/logrotate.d/yourapp

/var/log/yourapp/*.log {
    rotate 4
    daily
    size 5k
    missingok
    create
    compress
    notifempty
    delaycompress
}

sudo chmod u=rw,g=r,o=r /etc/logrotate.d/yourapp

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:

cat /var/lib/logrotate/status

Trigger logrotate manually:

sudo logrotate /etc/logrotate.d/

Empty a logfile as admin

Clear:

echo "" | sudo tee /var/log/logfile.log
cat /var/log/logfile.log

Append (-a):

echo "append this line" | sudo tee -a /var/log/logfile.log