Basic commands

head file: shows the first 10 rows of a file
less file : shows the content of the file (you can enter /searchterm oder %90 to jump in the file)
ln -s source destination : ln -s /etc/hosts ~/computers -> a shortcut computers will be created in your homedirectory
mkfs.ext3 /dev/sdc1 : format the disc /dev/sdc1 with the filesystem ext3
mount -o loop /mycd.iso /mnt : mount .iso file in a folder
newaliases: genearte the new file /etc/aliases.db from the file /etc/aliases
tail file : shows last 10 rows of a file
    tail -f file : shows the changes of the file in realtime
sendmail -v user@domain.com : send an e-mail to user@domain.com (you can write your message and set a dot (.) at the end to send the message
   sendmail -v user@domain.com < test.mail : sends the mail directly with test file test.mail as message
wget -r http://google.ch : saves the whole page recursivly