I have clients running webshops like oscommerce, clients having classifieds, auction and more. Some of them have cc processing, advanced scripts etc.

I wonder what the following commands might do to these sites or in
general what the function is i real life ??

I have looked at php.net and it say what it's for but I do not get that :-)

So:

disable_functions = exec, shell_exec, system, passthru

Can someone explain what that is, what it's good for and bad for and
in general if clients is affected or maybe it's not used often etc.

Note: I know what disable_functions is and why !

with those functions a user can act from php like he can act by logging via ssh...

http://www.php.net/exec



in my case i've also blocked proc_*, popen and other related functions...

if i want to grant shell access to a user i'll set up a chrooted "ambient" and give him access via ssh

softwares like oscommerce doesn't need shell access to work properly