Mostly useful for Ubuntu or debian based operating system.

Top 10 largest directories

du -a /var | sort -n -r | head -n 10

Find largest files on Linux

find / -size +10M -ls

find / -size +700M -ls

Top 10 processes by memory

ps aux --sort -rss | head

Bash check timing time measure

time ls /bin

time mongo --eval "db.users.find({})"

batch file extension renamer in bash

for file in *.png; do mv "$file" "basename $file .png.jpg" done

Create bootable disk (usb) from image

sudo dd bs=4M if=/home/$USERNAME/path/to/2014-09-09-wheezy-raspbian.img of=/dev/sdd

Update & upgrade packages

sudo apt-get update

sudo apt-get upgrade

Clean up packages for saving up disk space

sudo apt-get clean

Scan the local network for connected devices with IPs.

sudo apt-get install nmap

sudo nmap -sP

Python setup tools

sudo apt-get install python-setuptools

sudo easy_install

SSH into a remote computer

ssh name@hostname

Pipe both standart output and error into a file

Useful for logs

./some_binary >> logs.txt 2>&1

My usual run structure for unique log files:

./some_binary >> logs_date +%Y%m%d_%H%M%S.txt 2>&1 &