Linux

  1. Most Useful Unix Commands
  2. File and Directory Manipulation
  3. File Viewing and Editing
  4. File and Account Protection
  5. System and Process Information

To find out more about each command type man 'the command' (without the quotes) in the terminal

1. The Most Useful Unix Commands

man -k keywordList titles and descriptions of manual pages realted to your keyword
man [section-number] titleView the manual page called title. (The section-number is optional.)

2. File and Directory Manipulation

mv fromfile tofileMove or rename a file or directory
cp fromfile tofileCopy a file - like mv but fromfile is unchanged
rm filenameRemove (delete) a file. *Warning* There is no undelete, consider using rm -i for interactive deleting.
mkdir directory-nameMake a directory.
rmdir directory-nameRemove an empty directory. rm -r removes a directory and everything in it.
ls [options] [filename]List a file or directory. Try ls -l (long) or ls -a (all) to get more information about the same file or directory. If no filename is given, ls will print the current directory
cd [directory-name]Change to directory directory-name. If no directory-name is given, cd will put you in your home directory.
pwdPrint the name of your current directory. (Present Working Directory)

3. File Viewing and Editing

cat filenameQuick-and-dirty way to view a file.
more filenameLike cat, but does a whole lot more.
less filenameLike more, but does even more. (Don't ask)
vi filenameStandard Unix full-screen editor. Available everywhere.
emacs filenameAnother standard Unix editor.

4. File and Account Protection

passwdChange your password. DO THIS! Passwords should follow Heisenberg Uncertainty Principle. Loosly translated to mean: If someone sees it, change it.
chmodChange the mode (access rights) of a file or directory.
setfaclLike chmod only more powerful. A MUST read in the man-pages.
getfaclDisplays the file attributes set by setfacl.
chgrpChange the group ID of a file or dircetory.
umaskSet protection mask for file creation. umask 077 will help keep your files private.

5. System and Process Information

psSee running processes. Try ps -ef on Unix or ps -awux on Linux.
dfCheck drive sizes and mounted directories. Try df -k.
prstatReal-time view of running process and their status.
uptimeSee how long the system has been on for.
whoList users currently logged on to the system.

Thanks to http://www.cse.psu.edu/handouts/unix.html for the base of this information.