ctrl-s - freezes the screen, ctrl-q unfreezes it. Useful to stop output without stopping program
at Do job at certain time
cron Execute script at certain intervals (daily, weekly, etc.).
du -k -s directory Get directory size
find rootdir -name filename Look for filename starting with rootdir.
gzip zip/unzip
hexedit filename Edit a file in hex (access raw binary, not ASCII text)
kill-9 pid Kill any process. Signal 9 can't be ignored.
ln -s old new Symbolic link to directory.
netstat Prints open connections, ports, etc.
od -x file Octal dump (print file in octal). -x is hex flag.
ps List processes currently running. try "ps -u username"
reboot Can reboot machine remotely. Do "find / -name reboot"
shutdown now Shuts down a *nix box
su Get superuser priveledges, without logging in as root.
talk name@host Chat with another user
tar cvf myfile.tar files compress
tar xvf myfile.tar extract
tcpdump Print packets received by host. Try -Nt for succint output.
time operation Times how long an operation takes (time a.out)
traceroute dest Print hops from current host to dest (an ip addr or web page).
w or finger List users currently logged on.
ps -u username (get his processes and their pid)
$fpath - path variable
exec $SHELL -l - reload shell
sudo visudo - to edit /etc/sudoers
man hier - man page for directory structure
getfacl filename - to get acl of a file
setfacl -m u:user:rwx filename - to set acl for user on a file
setfacl -r u:user: filename - to remove acl for a user on a file