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Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

du and sort to find the biggest directories in defined filesystem
I had the problem that our monitoring showed that the "/" filesystem is >90% full. This command helped me to find out fast which subdirs are the biggest. The system has many NFS-mounts therefore the -x.

Complete TCP Handshake on a given host-port
Try to perform a fully TCP 3 way handshake on for a given host-port with a timeout of 1s.

Bash autocomplete case insensitive search
Change bash autocomplete case search to insensitive when pressing tab for completion.

tmux start new session with title and execute command
in this examp start htop command in tmux session over the shell cosole and set title for the tmux without doing it manuelly in tmux

scp a good script from host A which has no public access to host C, but with a hop by host B
middlehost allows ssh access from where you are but not securehost. Use nice ssh piping to simulate scp through A => B => C setting up the shell function if left as an exercise for the reader. ;-) Agent forwarding should avoid password typing.

Find all files with root SUID or SGID executables
Discovering all executables on your system that can be run as another user, especially root, is critical for system security. The above command will find those files with have SUID or SGID bits set and are owned by the root user or group.

alias to close terminal with :q
Put this in your ~/.bashrc file (or the equivalent) If you use vim a lot, this alias will be immediately obvious. Your brain will thank you.

Create incremental backups of individual folders using find and tar-gzip
Problem: I wanted to backup user data individually, using and incremental method. In this example, all user data is located in "/mnt/storage/profiles", and about 25 folders inside, each with a username ( /mnt/storage/profiles/mike; /mnt/storage/profiles/lucy ...) I need each individual folder backed up, not the whole "/mnt/storage/profiles". So, using find while excluding directories depth and creating two variables (tarfile=username & desdir=destination), tar will create a .tgz file for each folder, resulting in a "mike_2013-12-05.tgz" and "lucy_2013-12-05.tgz".

Remove a line in a text file. Useful to fix "ssh host key change" warnings


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