Introduction

Viewing logfiles in real time is one of the primary task for system administrators. Usually it is the end of the log file were new information is appended. Therefore the command tail -f LOGFILE is used. This document describes tail as well as other tools.

Tail

The Swiss knife for system administrators. The tool tail can be used for various purposes, the most common ones are:

1. View some lines at the end of a huge file: tail -n NUMBER FILE
2. View a logfile updating in real time (follow): tail -f FILE
3. Use it in scripts like: cat FILE|sort|uniq|tail -n 1

In cases more that one log file need to be monitored, many approaches have been implemented.

4. Quick and Dirty: cd /var/log&&tail -f mail.{err,warn,info,log}
5. Executing one tail per terminal
6. using screen and tail
7. using tmux and tail
8. …

Or one can use multitail

Multitail

The advantages of multitail over tail is that if you open 2 or more logfiles with one command in one window, unlike tail multitail will group the output. Installation is easy.

aptitude install multitail

Unfortunately the command line options differ from tail, but some are similar.

1. View some lines at the end of a huge file: multitail -n NUMBER FILE
2. View a logfile updating in real time (follow): multitail -f FILE
3. Use it in scripts like: cat FILE|sort|uniq|mailtail -j -n 1 will not work
4. View many files: cd /var/log&&multitail -f mail.{err,warn,info,log}

Some differences to tail are:

• Leaving the multitail session with q not CTL-C
• Output is colorful
• Compared to tail, multitail is difficult to use in scripts
• Displays the filename per default

Grc

If the color feature of multitail would be the only reason to switch from tail to multitail, then one should consider using grc to colorize tail.

For mail logs grc creates in my opinion better color outputs, because it highlights some constructs, like round and square brackets content and the header of a syslog line can be easily distinguished from the rest.

aptitude install grc

• See grc for advanced usage of grc
• Repository: https://github.com/garabik/grc

History

Version	Date	Notes
0.1.1	2022-05-28	Link to grc & grc repository, +History, mv ../Tools
0.1.0	2022-05-27	Initial release