free -k/m/g information on machine's memory
top information on processes running
du {path} disk usage
df free space
ps processes running on your account
w\who logged in users information
find / -name 'file_name' find a file/directory
rm -r remove directory
stat {file_name} display file status
crontab -l list all crontab jobs
crontab -e edit crontab file
which {command}/type {command} show path of a command