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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" }

Simplest port scanner
Very handy way to perform a host scan if you don't have nmap,ncat,nc ...or other tools installed locally. When executing a command on a /dev/tcp/$host/$port pseudo-device file, Bash opens a TCP connection to the associated socket and UDP connection when using /dev/udp/$host/$port.A simlpe way to get servers banner is to run this command "cat < /dev/tcp/localhost/25" , here you will get mail server's banner. NOTE: Bash, as packaged for Debian, does not support using the /dev/tcp and /dev/udp pseudo-device it's not enabled by default Because bash in Debian is compiled with ?disable-net-redirections.

Prevent non-root users from logging in
Also with optional message: $ echo "no login for you" > /etc/nologin (This doesn't affect your current X session - you're already logged in!)

Generate random passwords (from which you may select "memorable" ones)
See: "man pwgen" for full details. Some Linux distros may not have pwgen included in the base distribution so you maye have to install it (eg in Mandriva Linux: "urpmi pwgen").

Search some text from all files inside a directory

Convert files from DOS line endings to UNIX line endings
This method will also convert mac line endings.

Download latest released gitlab docker container
Download latest released gitlab docker container

Silently Execute a Shell Script that runs in the background and won't die on HUP/logout
This command runs your shell script in the background with no output of any kind, and it will remain running even after you logout.

Backup of a partition
Clone a partion with tar.

list all files in a directory, sorted in reverse order by modification time, use file descriptors.
It's both silly, and infinitely useful. Especially useful in logfile directories where you want to know what file is being updated while troubleshooting.


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