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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" }

Check for login failures and summarize
This command checks for the number of times when someone has tried to login to your server and failed. If there are a lot, then that user is being targeted on your system and you might want to make sure that user either has remote logins disabled, or has a strong password, or both. If your output has an "invalid" line, it is a summary of all logins from users that don't exist on your system.

list block devices
Shows all block devices in a tree with descruptions of what they are.

Convert tab separate file (TSV) to JSON with jq
With this command you can convert a tab separate file (TSV) into a JSON file with jq. For example, this input.tsv i-0b9adca882e5e6326 172.16.0.188 i-088dd69e5c3624888 172.16.0.102 i-0e70eac180537d4aa 172.16.0.85 will produce the showed output.

Clean swap area after using a memory hogging application
When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again. Both swapoff and swapon require root privileges.

Alias to securely run X from tty and close that tty afterwards.
There are different ways to run X, I prefer to run it without xdm/gdm. The problem is you can't lock X because one can press Ctrl+Alt+F1, press Ctrl+Z and kill you X locking process. Of course you can disable Ctrl+Alt* or Ctrl+Alt+Backspace keys, but it's inconvinient if you really need to switch into console.

docker kill all containers

Remove all the files except abc in the directory
Finds all files in the current directory and deletes them besides file called "abc"

ping a host until it responds, then play a sound, then exit
Audio acknowledgement for host availability. When running the command from a Linux systems, you can use "festival" or "espeak" instead of "say".


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