Hi Sebastian,

On Mo 16 Sep 2013 16:17:31 CEST Sebastian Flothow wrote:

I did some further testing, and the resume failures are indeed due
to missing AFS tokens. When suspending a session, the SSH connection
is closed, sshd will call pam_close_session(), which means that
pam_krb5 and pam_afs_session will delete the user's ticket/token
(resp.). The session therefore loses access to the home directory
and appears to freeze up, preventing it from being resumed.

Both pam_krb5 and pam_afs_session accept retain_after_close as a
parameter, which disables the delete-on-close behavior. With this
parameter set, it becomes possible to resume sessions, unless the
AFS token has expired.

Thanks for digging this out. Good work!!!

This solves at least the case where the user reconnects quickly (eg.
after a short network outage), but it still means sessions will
become unresumable when left unused for a few days.

I get that. NFSv4 with Kerberos is very similar to the AFS token behaviour.

I guess the only way to avoid this is to not store session data in
the home directory. Can X2go be configured such that it uses eg.
/tmp or /var/lib for this purpose?

In earlier versions of X2Go every session detail was in $HOME. Some of
the session information has to be accessible by super-user root. Those
bits, I have already moved out of the home (e.g. the session.log file).

Normally, the AFS token should be immediately restored after SSH login
(which is the first action taken when resuming a session). However,
this AFS token does not re-awake the session so it can be resumed. The
question is why...

Does a session simply not resume (with an x2goagent still being
present for this session)? Or does the x2goagent crash somewhere on
the run (i.e. when the session is suspended and the AFS home freezes
some time later)?

When evoking x2golistsessions, the first field of each output line is
the x2goagent PID that is associated to that session in the same line.
With non-resumable sessions, please check if the x2goagent processes
remain active on the X2Go server or if the x2goagent processes crash
(disappear). I can only imagine that the x2goagent processes remain
alive (frozen) until the AFS token gets reinstated by the X2Go
resuming SSH login. If x2goagent crashes somewhere on the way, we have
to find out why and how to prevent it.

However, if x2goagent stays functional, we have to investigate, if
there is anything AFS-critical in /usr/bin/x2goresume-session. If you
look at the script /usr/bin/x2goresume-session, can you spot anything
that might fail on AFS?

Greets, Mike

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