what is log file

The configuration for logrotate is typically stored in a file called logrotate.conf or in a file within the /etc/logrotate.d/ directory. The format of the configuration file is fairly simple and consists of directives and options that specify how logrotate should behave.

Here is an example logrotate.conf file:

# specify the location of the log files
/var/log/messages {
  # rotate the log files every day
  daily
  # keep 30 rotated copies of the log files
  rotate 30
  # compress the rotated log files
  compress
  # delay compression of the rotated log files until the next rotation
  delaycompress
  # create a new log file after rotating the old one
  create
  # set the owner and group of the new log file
  owner root
  group root
  # set the permissions of the new log file
  mode 0644
}

# specify the location of another set of log files
/var/log/nginx/*.log {
  # rotate the log files when they reach a size of 100MB
  size 100M
  # keep 3 rotated copies of the log files
  rotate 3
  # compress the rotated log files
  compress
  # delay compression of the rotated log files until the next rotation
  delaycompress
  # create a new log file after rotating the old one
  create
  # set the owner and group of the new log file
  owner root
  group root
  # set the permissions of the new log file
  mode 0644
}

In this example, the first block specifies that the log files in the /var/log/messages directory should be rotated daily, with 30 rotated copies kept and compressed. 

The second block specifies that log files in the /var/log/nginx directory with a .log extension should be rotated when they reach a size of 100MB, with 3 rotated copies kept and compressed.

You can also use logrotate to specify a script to be run before or after the log files are rotated. This can be useful for tasks such as restarting services or sending notifications when log rotation occurs.

and the majority of the commonly used directives are listed below:

1.      compress: This directive specifies whether the rotated log files should be compressed to save space.

2.      compresscmd: This directive specifies the command to use for compressing rotated log files.

3.      compressext: This directive specifies the extension to use for compressed log files.

4.      compressoptions: This directive specifies options to pass to the compression command.

5.      copy: This directive specifies that the log file should be copied, rather than moved, when it is rotated.

6.      copytruncate: This directive specifies that the log file should be truncated (emptied) after it is copied for rotation.

7.      create: This directive specifies the permissions and ownership of the rotated log files.

8.      dateext: This directive specifies that a date stamp should be added to the rotated log file names.

9.      dateformat: This directive specifies the format of the date stamp that is added to rotated log file names.

10.   delaycompress: This directive specifies whether the rotated log files should be compressed, but not until the next rotation.

11.   ifempty: This directive specifies whether log rotation should occur even if the log file is empty.

12.   include: This directive specifies additional configuration files to be included in the current configuration.

13.   mail: This directive specifies an email address to which a message should be sent after log rotation.

14.   mailfirst: This directive specifies that a message should be sent before log rotation.

15.   maillast: This directive specifies that a message should be sent after log rotation.

16.   maxage: This directive specifies the maximum number of days that a rotated log file should be kept.

17.   missingok: This directive specifies that logrotate should continue even if the log file does not exist.

18.   monthly: This directive specifies that log rotation should occur on a monthly basis.

19.   nocompress: This directive specifies that rotated log files should not be compressed.

20.   nocopy: This directive specifies that the log file should be moved, rather than copied, when it is rotated.

21.   nocopytruncate: This directive specifies that the log file should not be truncated after it is copied for rotation.

22.   nomail: This directive specifies that no message should be sent after log rotation.

23.   noolddir: This directive specifies that rotated log files should not be placed in a separate directory.

24.   nosharedscripts: This directive specifies that the postrotate script should not be run for each rotated log file.

25.   notifempty: This directive specifies that log rotation should not occur if the log file is empty.

26.   postrotate: This directive specifies a script to be run after log rotation.

27.   prerotate: This directive specifies a script to be run before log rotation.

28.   rotate: This directive specifies the number of rotated log files that should be kept.

29.   sharedscripts: This directive specifies that the postrotate script should be run for each rotated log file.

30.   size: This directive specifies the maximum size that a log file should reach before it is rotated.

31.   weekly: This directive specifies that log rotation should occur on a weekly basis.

lastaction keyword

It is a keyword that is used in the configuration file for the `logrotate` utility. 

The `lastaction` keyword specifies the script or command that should be run after all the log files have been rotated. In the configuration file, the script or command that is specified with the `lastaction` keyword is placed between `lastaction` and `endscript` keywords.

Here is an example of how the `lastaction` keyword might be used in a logrotate configuration file:

/var/log/myapp.log {
    rotate 7
    compress
    delaycompress
    copytruncate
    lastaction
        /usr/local/bin/myapp-log-cleanup
    endscript
}

In this example, the lastaction keyword specifies that the script /usr/local/bin/myapp-log-cleanup should be run after the log file /var/log/myapp.log has been rotated. The script specified with the lastaction keyword can perform any desired actions, such as deleting old log files or sending an email notification.

you can get full list of commands used in logroate configuration file by checking the man Page: man logrotate