Randy McMurchy wrote:
> 
> Just for my FYI, (and sorry for not being able to answer this myself
> due to no time for recent BLFS), what does having X installed do to
> a Linux-PAM build?
> 
> I've always installed cracklib/PAM/Shadow before X so I cannot say
> or determine what may or may not be different.
> 

Yes, it's a reciprocal dependency.  Proper order is as you have it but 
later to rebuild Linux-PAM.

I hadn't quite figured out what to do with su and sudo yet.  Wasn't sure 
if requisite would fail if the module didn't exist, but optional seems 
to be the appropriate control in this situation anyway (since we don't 
know if it exists).  I was just over thinking it I guess.  I'll get 
/etc/pam.d/su updated in a sec.  Anyway, to directly answer your 
question, it provides pam_xauth which IIUC creates $XAUTHORITY for the 
target user with the current xauth session key for use with su (and 
later, for sudo when /etc/pam.d/su is copied).  From the 
modules/pam_xauth/README file:

pam_xauth — PAM module to forward xauth keys between users

--------------------------------------------------------------------------

DESCRIPTION

The pam_xauth PAM module is designed to forward xauth keys (sometimes 
referred to as "cookies") between users.

Without pam_xauth, when xauth is enabled and a user uses the su(1) 
command to assume another user's priviledges, that user is no longer 
able to access the original user's X display because the new user does 
not have the key needed to access the display. pam_xauth solves the 
problem by forwarding the key from the user running su (the source user) 
to the user whose identity the source user is assuming (the target user) 
when the session is created, and destroying the key when the session is 
torn down.

-- DJ Lucas

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