[plug] the problem with starting X - fixed

[Jason Nicholls]

G'day all,

Don't know whether you noticed, but before I began my talk I couldn't get
Xwindows to start in the usual way (startx). Matt suggested I use xdm to get
around the problem which solved it temporarily for the presentation.

Well it was bugging me, of course, and I couldn't get to sleep until I found out
why. Here is a run down of what I did to find a real solution:

	- performed traces on the process to see what was happening.
	  (strace -v -f startx)
	- I discovered the problem was something to do with Xwrapper, which is
	  a suid root wrapper script.
	- the trace would keep showing up the error EPERM when trying to
	  execute Xwrapper. I didn't know what this stood for so I went a
	  searching (from the execve man page):

		EPERM   The process is being traced, the user is not the 
			superuser and the file has an SUID or SGID bit set.
	- OK, this was telling me I couldn't actually see what Xwrapper was
	  doing because it was SUID and I wasn't the super user (logged in as
	  jason). As a temporary measure I SUID root strace so I can get
	  around this problem.
	- Now the trace is *much* more informative and I find out the problem
	  is occuring when Xwrapper (or some related thing like pam_console)
	  tries to read the file /var/lock/console/jason. I check the
	  permissions with rpm first (rpm -V filesystem) and
	  discover it's wrong for the /var/lock directory (I also check on 
	  another RH box).
	- I fix the permissions and it all works again.

I havn't got a clue why the permission had changed, can file system errors do
this sort of thing? My laptop battery emptied out recently without linux
shutting down...


Later,

Jason Nicholls
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Jason Nicholls    icq: 11745841    email: <jason at mindsocket.com.au>
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