OpenVPN comes with example-scripts to update /etc/resolv.conf using "resolvconf" or systemd-resolvconf. I don't use one of them therefore I modified the script so that it simply changes /etc/resolv.conf directly. I placed a variable "IMMUTEABLE" in this script. If IMMUTEABLE is set to 1, this script will change the fileattribute of /etc/resolv.conf to immuteable. In that way it is possible to prevent other programms like dhcp-clients to change /etc/resolv.conf while openvpn is running.

GNU parallel is an amazing command line tool for executing jobs in parallel using one or more machines. It has a lot of features and therefore a lot of options. Fortunately the manual page is full of examples.

Most linux-users know $OLDPWD. It's an environment variable to get the recently used directory. Sometimes it would be nice to remember more visited directories. In such cases pushd and popd would be a good choice..

Most common shells do have a directory stack. By looking in the man-page of bash I found the following description of the DIRSTACK:

echo error >&2

Magnificent app which corrects your previous console command, inspired by a @liamosaur tweet.

A sysadmin needs his tools.  I really need at least 3 tools to be productive:

1. Terminal-Emulator (or screen/tmux if I am working without X)
2. Shell
3. Editor

This is my Rule Of Three. Those 3 tools can make my life much easier. Therefore I have to choose those tools wisely. And of course I have to know them very well, so I can get all the benefits of them. In this article I want to introduce one of my "favourite" shells: zsh

http://www.tecmint.com/mysterious-uses-of-symbol-or-operator-in-linux-commands/

Sometimes it is useful to compare to directories and display the differences. diff can do the trick for you

diff -r dir1/ dir2/

If you just want a overview about the differences then just use "brief":

diff --brief -r dir1/ dir2/

git can show you the differences too, and it can do it colorful if you want

git diff dir1/ dir2/

dr@tardis> for i in `ls -d *`; do du -hs $i; done
4,0K    cron-job.txt
48K     etc
4,0K    install.sh
4,0K    README.Debian.TXT
4,0K    README.TXT
16K     usr