Useful Linux command compilation

Set system date/time

: date -s "17 OCT 2010 13:00:00"

: hwclock -systohc


Change the time stamps of files

: touch foo


File Permissions

chmod -R ugoa =+- rwx filename
       ^ ^^^^ ^^^ ^^^     ^
       | |||| ||| |||     |
       | |||| ||| |||     \---------- file or directory
       | |||| ||| |||                 --------------------
       | |||| ||| ||\---------------- Execute
       | |||| ||| |\----------------- Write
       | |||| ||| \------------------ Read
       | |||| |||                     --------------------
       | |||| ||\-------------------- Remove
       | |||| |\--------------------- Add
       | |||| \---------------------- assign
       | ||||                         --------------------
       | |||\------------------------ All
       | ||\------------------------- Others
       | |\-------------------------- Group
       | \--------------------------- User
       |                              --------------------
       \----------------------------- Recursively 
                                      --------------------
       Usage: chmod g+w filename
 

From : http://en.wikibooks.org/wiki/Linux_Guide/Using_the_shell 

An excellent resource of information with clear explanations