Tag Archives: linux

Add Line Numbers to “cat” Output

cat can be used to print the contents of a file in a Terminal, and it’s often useful to number each line of the output (including empty lines). Adding line numbers is as simple as adding the -n switch to the command: cat -n filename.txt Example Output, with -n switch: $ cat -n filename.txt 1 Line …

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Using grep and Ignoring Case (Case Insensitive grep)

grep is a great way to find phrases, words, and characters in text.  One of the biggest stumbling blocks is case – is the word “Hello”, “hello”, “HELLO”, or even “HeLLo”?  All of these are different, and a “grep “Hello”” would only find lines containing the first “Hello” example. You can, however, exclude case from …

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Using dig to Query a Specific DNS Server (Name Server) Directly (Linux, BSD, OSX)

There may be occasions when you wish to query a DNS server directly.  I often do it before changing DNS servers for a domain; I’ll setup the new records on the new DNS servers, and then query them directly to ensure they are returning the correct records. I recommend that anyone running DNS services for …

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Using grep to Exclude Lines Containing Certain Characters/Text

I like to watch Apache log files using tail -f but they often get filled up with data I don’t want/need to see – like, when I access the web site. grep is a great tool to search for certain information in text files – but it can also exclude certain pieces of information which …

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Kill a GNU Screen Session from the Command Line

This article is about GNU Screen – you can read about GNU Screen here: http://www.gnu.org/software/screen/ There may be times when you have multiple, or even a single, screen session which you want to kill without attaching to it and ending it as you normally would. You can kill a screen session using the session ID or the …

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Removing packages only installed as dependancies and no longer needed (Ubuntu, Debian)

We’ve all installed packages, using apt-get, where it’s installed a lot of other packages to satisfy dependancies. But what if you remove that package at a later date that needed all of those dependancies?  You’ll probably find it’s left the dependancies installed.. and if you’ve not installed any other packages which also need those dependacies, …

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Finding out when (and where from) a user last logged into a Linux/BSD machine

There may be times when you want to find out when and where from a user last logged into a Linux or BSD machine. Of course, you could trawl through auth logs, but there is a quicker way by using “lastlog“. lastlog is a command which shows you the last login time and also from …

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Viewing Another Users’ Crontab Entries in Ubuntu, Debian or CentOS

There may be occasions where you, as the administrator of a machine, may want to see what cron entries your users have.  Maybe you have slow downs at a particular time every day, and want to see who’s running what. All crontab’s, for all users, are stored in /var/spool/cron/crontabs on Debian and Ubuntu, as plain …

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