A table of commands that were useful to me when I first began using Linux. Note that all of these may not apply to your particular distribution, configuration, etc.

adduser USERNAME
Create a new user
alias quit='exit'
Be able to type quit and accomplish the same thing as exit
Ctrl-Alt-FUNCTION_KEY
Switch consoles
apt-cache search PROGRAM
Find a particular program and its spec.s
apt-get clean
Clears out retrieved package files, frees disk space
apt-get install PROGRAM
Install PROGRAM
apt-get install PROGRAM --fix-broken
Fix the broken PROGRAM
apt-get install PROGRAM --fix-missing
Pick up where you left off
apt-get dist-upgrade
Updates everything
apt-get remove PROGRAM
Uninstalls PROGRAM
apt-get update
Do before running apt-get dist-upgrade
aumix
A tool to adjust volume
chmod NUMBER FILE
Change permissions on FILE
depmod MODULE
Lists the dependencies for MODULE
df -h
Lists partitions and their sizes, how much of them has been used, and how much space is left on each
du -h
Shows how much space has been used in the current directory
free -m
Lists the total mem./swap free/total/used/etc. in megabytes
groups
Lists the groups the current user is in
insmod
Add a module
kill -9 PID
If a program has gotten out of control, run ps aux to find out its PID (second column); then, use this command to end that program
ln -s SOURCE DESTINATION
Link something symbolically
lpr -P PRINTER FILE
Print FILE with PRINTER
ls
Lists the files in the current directory
ls -al
Lists the files in the current directory; shows “hidden” files and more information
lsmod
Lists the current active modules
man PROGRAM
Displays a manual for PROGRAM
modprobe MODULE
Activates MODULE
mount WHAT WHERE
Mount WHAT at location WHERE
nslookup URL
Finds an IP address for URL
passwd USER
Changes the password for USER
ps aux
Lists all running processes
rmmod MODULE
Remove MODULE if it is active
rpm --test -Uvh RPM
Test RPM for errors
rpm -Uvh RPM
Install RPM
startx
Start an X session
su
Become root
su USER
Become USER
shutdown -r now
Reboot computer
shutdown -h now
Shut off computer
tar jxvf FILE
Decompress a .tar.bz2 file
tar zxvf FILE
Decompress a .tar.gz file
tar zcvf FILENAME.tar.gz STUFF
Create a .tar.gz archive called FILENAME.tar.gz of STUFF
top
Displays a list of processes and CPU/memory usage
umount DIRECTORY
Unmount DIRECTORY
xv -root -rmode 9 -quit IMAGE
Make IMAGE your desktop wallpaper