Truncate Log Files

This section provides a tutorial example on how to truncate log files in Linux computers.

If you are running some server programs on your Linux computer, you may see some large log files on the hard disk. For example, the following command shows a log file with 74 MB of an old Apache Web server:

herong$ ls -l /var/log/apache2/error_log
-rw-r--r--  1 root  wheel  74947393 Nov  6 10:37 /var/log/apache2/error_log

To save disk space, you should save a backup copy in an offline storage and truncate the log file to zero byte.

Here are some general guidelines on truncating log files.

1. Do not truncate the log file, if it is already rotated by the server program. For example: the following command shows rotated log files of an Apache Web server.

herong$ sudo ls -l /var/log/httpd/
-rw-r--r--. 1 root root     441 Oct 31 03:27 error_log
-rw-r--r--. 1 root root    7576 Oct 10 03:25 error_log-20211010
-rw-r--r--. 1 root root    1505 Oct 17 03:26 error_log-20211017
-rw-r--r--. 1 root root    5760 Oct 24 03:10 error_log-20211024
-rw-r--r--. 1 root root    6576 Oct 31 03:27 error_log-20211031

2. Do not delete the log file using the "rm" command. Some server program will crash, if its log file is gone. Also re-creating an empty log file with the original permissions takes multiple commands.

3. Redirect empty output to the log file. Here are some example commands:

herong$ : > /var/log/apache2/error_log

herong$ echo -n /var/log/apache2/error_log

herong$ cat /dev/null > /var/log/apache2/error_log

4. Add "sudo" command, if you don't have "write" permission on the log file. Here are some example commands:

herong$ sudo sh -c ': > /var/log/apache2/error_log'

herong$ sudo sh -c 'echo -n /var/log/apache2/error_log'

herong$ sudo sh -c 'cat /dev/null > /var/log/apache2/error_log'

herong$ cat /dev/null | sudo tee /var/log/apache2/error_log

5. Use "truncate" command as shown below:

herong$ truncate -s 0 /var/log/apache2/access.log

herong$ sudo truncate -s 0 /var/log/apache2/access.log

Table of Contents

 About This Book

 Introduction to Linux Systems

 Cockpit - Web Portal for Administrator

 Process Management

Files and Directories

 "find" - Search for Files

 "more", "head" and "cat" - Read Files

 "split" and "cat" - Split and Join Files

Truncate Log Files

 "compress/uncompress" - Compressed *.Z Files

 "gzip/gunzip" - Compressed *.gz Files

 "xz/unxz" - Compressed *.xz or *.lzma Files

 "tar -c" and "tar -x" - Create and Extract Archive Files

 "zip" and "unzip" - Create and Extract ZIP Files

 "Operation not permitted" Error on macOS

 Users and Groups

 File Systems

 Block Devices and Partitions

 LVM (Logical Volume Manager)

 Installing CentOS

 SELinux - Security-Enhanced Linux

 Network Connection on CentOS

 Internet Networking Tools

 SSH Protocol and ssh/scp Commands

 Software Package Manager on CentOS - DNF and YUM

 vsftpd - Very Secure FTP Daemon

 LDAP (Lightweight Directory Access Protocol)

 Administrative Tasks


 Full Version in PDF/EPUB