When supporting systems you have inherited or in environments that have many different OS versions and distributions of Linux. There are times when you simply don't know off hand what OS version or distribution the server you are logged into is.
Luckily there is a simple way to figure that out.
Ubuntu/Debian $ cat /etc/lsb-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=13.04 DISTRIB_CODENAME=raring DISTRIB_DESCRIPTION="Ubuntu 13.04" RedHat/CentOS/Oracle Linux # cat /etc/redhat-release Red Hat Enterprise Linux Server release 5 (Tikanga) Catchall If you are looking for a quick way and don't care what the output looks like, you can simply do this as well....
Today's article is going to cover a command that falls into the “I don't use this often, but when I do it's awesome” category.
The tac command is very similar to the cat command in that it is used to concatenate and print files. However there is one very large difference, the tac command does this in reverse, starting with the last line of the file and working its way up to the first line....
The grep command is a command that most Linux users learn early on, and many times they learn to use it via pipes (stdin). Because of this some Linux users just assume that grep can only be used with stdin; it's ok, I was one of those too!
Before I continue with some grep tricks I want to clarify the basic grep usage.
Stop Doing This:
$ cat file.log | grep "something" something Do This More:...
In the world of Cloud Servers and Virtual Machines scripting and automation are top priority for any sysadmin. Recently while I was creating a script that logged into another server via SSH to run arbitrary commands, I ran into a brick wall.
$ ssh 192.168.0.169 The authenticity of host '192.168.0.169 (192.168.0.169)' can't be established. ECDSA key fingerprint is 74:39:3b:09:43:57:ea:fb:12:18:45:0e:c6:55:bf:58. Are you sure you want to continue connecting (yes/no)? To anyone who has used SSH long enough the above message should look familiar....
Adding and Modifying Users and Groups is a core systems administration task. The act of adding a user and group is fairly easy however there are some tricks that help make the long-term management of users easier.
Tips for easier management Keep user attributes consistent amongst all systems A common mistake sysadmins make when building a new environment is they will allow uid's, gid's, home directories and other user attributes to be mis-matched from system to system....