$ df -h ( hit enter )
Will return something similar to:
Filesystem Size Used Avail Use% Mounted on /dev/sda5 128G 80G 47G 64% / /dev/sda2 2.0G 264M 1.6G 15% /tmp /dev/sda1 99M 23M 71M 25% /boot tmpfs 16G 0 16G 0% /dev/shm
Tags: command line, hard drive size, server, ssh