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Get last sleep time on a Mac
Similarly for last wake time: $ sysctl -a | grep waketime

Displays the attempted user name, ip address, and time of SSH failed logins on Debian machines
A variation of a script I found on this site and then slimmed down to just use awk. It displays all users who have attempted to login to the box and failed using SSH. Pipe it to the sort command to see which usernames have the most failed logins.

a function to find the fastest DNS server
http://public-dns.info gives a list of online dns servers. you need to change the country in url (br in this url) with your country code. this command need some time to ping all IP in list.

Watch and cat the last file to enter a directory
Great for watching things like Maildir's or any other queue directory.

Running scripts after a reboot for non-root users .
Sometimes we may want to run a script when a system reboots . We can simply do this by just scheduling the script using vixie cron with the @reboot option . e.g @reboot I use it to send me an alert message on our prod hosts to send an alert message when the system reboots . @reboot zaman uptime | echo `uptime` | mail -s "`uname -n` got rebooted" me@myhost.com

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Random colours at random locations

list files recursively by size

use jq to validate and pretty-print json output
the `jq` tool can also be used do validate json files and pretty print output `cat file.json | jq` available on several platforms, including newer debian-based systems via `#sudo apt install jq`, mac via `brew install jq`, and from source https://stedolan.github.io/jq/download/

Create a single-use TCP (or UDP) proxy
Redirect the local port 2000 to the remote port 3000. The same but UDP: $ nc -u -l -p 2000 -c "nc -u example.org 3000" It may be used to "convert" TCP client to UDP server (or viceversa): $ nc -l -p 2000 -c "nc -u example.org 3000"


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