Generate a random password 30 characters long

$ strings /dev/urandom | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo

Checking disk usage

$ sudo apt-get install terminator

Alt+F2 > terminator

$ df -h
$ lsblk

Check open ports

$ sudo lsof -Pni4 | grep LISTEN

$ sudo lsof -i -P | grep -i "listen"

or

$ sudo su -

# lsof -Pni4 | grep LISTEN

# lsof -i -P | grep -i "listen"

Show apps that are using the Internet connection at that moment

Open Terminal, CLI, Terminator , and enter this line...

$ lsof -P -i -n | cut -f 1 -d " "| uniq | tail -n +2

Get your external IP address

Get your external IP address

$ $ curl -s http://checkip.dyndns.org/ | grep -o "[[:digit:].]\+"

or

$ dig +short myip.opendns.com @resolver1.opendns.com

or

$ curl ip.appspot.com

or

$ sudo apt-get install curl

$ curl ifconfig.me

$ watch -n 1 "netstat -tpanl | grep ESTABLISHED"
Monitor TCP opened connections

How to check Linux version from command line

$ cat /proc/version

Ubuntu / Xubuntu

$ cat /etc/lsb-release

Check if a machine is online

$ ping -c 1 -q MACHINE_IP_OR_NAME >/dev/null 2>&1 && echo ONLINE || echo OFFLINE