older Red hat versions

[Bevan C. Bennett]

> 1) My friend has written a script and wants it to automatically run if a
> certain user logins in( how can he add the script to automatically run
> when he logs on)

There are many ways to accomplish this, depending on complexity, which 
vary slightly depending on the "certain user's" choice of shell.

If you don't mind that the user can see and mess with this 
functionality, just add a line to run the script into the user's startup 
files (~/.profile for bash or ~/.login for tcsh).

If you don't want the user to know, then the following might be more useful:

For tcsh and csh, the administrator could edit /etc/csh.login, which 
gets executed (before the user's .login) on login and add something like:
if ( $USER == "username_in_question" )
      /bin/sh /etc/script_to_run.sh
		[or]
      include /etc/script_to_run.csh
endif

For bash and sh, edit /etc/profile instead with something like:
if [ "$USER" == "username_in_question" ]; then
      . /etc/script_to_run.sh
		[or]
      /bin/csh /etc/script_to_run.csh
fi

WARNING: Many countries have laws regarding how and if one may be 
monitored without notification.  If your friend intends to use this to 
covertly log or monitor unaware users (and not for other useful purposes 
or geneeral amusement) he/she should check his/her locally applicable laws.