Viewing files, up close and personal
Heads or Tails?
Although less can be powerful, sometimes it – and even more or cat – can be imprecise or overkill for what you want. In many circumstances, you might want to turn to head or tail instead.
As the name implies, head looks at the first 10 lines of a file by default. Probably its greatest use is to let you identify a file quickly. For instance, if you were logged in as the root user and unsure what information /var/log/scrollkeeper.log contained, head might be just enough for you to find that answer.
In contrast, tail looks at the last 10 lines of a file and often writes them to the command line. This glimpse is useful because system log files generally write the latest information at the bottom of the file, and it is ideal for ongoing monitoring for troubleshooting. All you need to do is open a terminal on an unused virtual desktop and continue your work on another, glancing occasionally at the output from tail to see what is happening.
If 10 lines are not enough, use -<number> to change the number of lines displayed in either head or tail. If you want to see the file header, which can contain such information as the name of the file or information that identifies its format, then use the -v (verbose) option (Figure 5). Alternatively, you can suppress the head with -q (quiet).
Additionally, tail has several commands to help you to manipulate troubleshooting information. If you add -f, information will be added to the output as it becomes available. Should the monitored file be inaccessible or become so, you can use --retry to ensure that you keep monitoring it (or, conversely, to ensure that the reason you haven't received new data isn't that something has happened to the file). To control how often the file is scanned and reduce the amount of system resources used by tail, add -s<SECONDS>.
Still another useful feature is --pid<PID>, which stops tail from running if the system process with the specified ID stops running. Most likely, you will need to run the top or ps commands as the root user to find the PID of the process you want to monitor.
A Basic Beginning
These options are not the only ones you can use with the viewing commands. In particular, less has dozens more, some of which you are unlikely to use unless you have advanced skills in system administration and troubleshooting. Still, the ones mentioned here should help you use the commands efficiently without getting bogged down in too much memorization. Take a look at the man page for the command of your choice. The view commands are not complicated – even if the way options are described in their man pages sometimes are.
« Previous 1 2
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.
-
Canonical Collaborates with Qualcomm on New Venture
This new joint effort is geared toward bringing Ubuntu and Ubuntu Core to Qualcomm-powered devices.
-
Kodi 21.0 Open-Source Entertainment Hub Released
After a year of development, the award-winning Kodi cross-platform, media center software is now available with many new additions and improvements.
-
Linux Usage Increases in Two Key Areas
If market share is your thing, you'll be happy to know that Linux is on the rise in two areas that, if they keep climbing, could have serious meaning for Linux's future.
-
Vulnerability Discovered in xz Libraries
An urgent alert for Fedora 40 has been posted and users should pay attention.
-
Canonical Bumps LTS Support to 12 years
If you're worried that your Ubuntu LTS release won't be supported long enough to last, Canonical has a surprise for you in the form of 12 years of security coverage.
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.