Useful Linux commands

grep

grep -nr 'yourString*' .

The dot at the end searches the current directory. Meaning for each parameter:

-n            Show relative line number in the file
'yourString*' String for search, followed by a wildcard character
-r            Recursively search subdirectories listed
.             Directory for search (current directory)

How to grep ps output with headers

ps -ef | egrep "Download|PID"

FreeBSD

• su:

     The su utility requests appropriate user credentials via PAM and switches
     to	that user ID (the default user is the superuser).  A shell is then
     executed.