Re: FcgidAccessChecker hangs. (Apache Users)

Thanks for looking into this, Jeff; I've attached an strace with
mod_fcgid (strace-fcgid), one with mod_fastcgi (strace-fastcgi) and
one with mod_fcgid and relative time stamps so you can see where it
hangs (strace-fcgid-with-relative-time).

Ouch. Is your script running in there somewhere? I just saw httpd activity but no activity of your script. (s/script/application/)

Perhaps the most straightforward way to get a trace is to start httpd, identify the mod_fastcgi or mod_fcgid daemon process, start strace -fp DAEMON-PID, and then make the request.

How to identify the mod_fcgid daemon: At startup, it logs a message at LogLevel info which says "mod_fcgid: Process manager XXXX started", where XXXX is the pid.

mod_fastcgi? I don't know. But you may be very used to gdb and strace before this is over, so maybe you can pick the child that doesn't look like the others ;)

--/--

OTOH, how much effort is required to get your chicken-scheme script running on Linux?

It looks like the immediate call is:

rt_sigtimedwait(~[ILL TRAP ABRT BUS FPE KILL SEGV USR2 PIPE CONT
STOP SYS RTMIN RT_1], NULL, NULL, 8) = 1

> On Sunday, November 11, 2012, Peter Danenberg wrote:
>
> > Digging a little deeper, mod_fcgid hangs on line 318 of
> > fcgid_bridge.c:
> >
> > ap_scan_script_header_err_core(r, sbuf, getsfunc_fcgid_BRIGADE,
> > brigade_stdout)
> >
> > I don't know enough about ap_scan_script_header_err_core yet to figure
> > out why this might be the case.
>
>
> Can You compare an strace/truss/dtruss of your script running with the
> alternative modules?
>
> >
> > > The following trivial script,[1] which simply returns a 200 header,
> > > hangs under FcgidAccessChecker:
> > >
> > > (call-with-dynamic-fastcgi-query
> > > (λ (query)
> > > (display-status-&c.)))
> > >
> > > The same script works fine under mod_fastcgi with
> > > FastCgiAccessChecker; or handled as an fcgid-script or fastcgi-script.
> > >
> > > The output from error_log is as follows:
> > >
> > > [Sun Nov 11 01:39:44 2012] [info] mod_fcgid: server
> > > localhost:/usr/local/var/html/scm/api/access.scm(15965)
> > > started
> > >
> > > [Sun Nov 11 01:40:24 2012] [warn] [client 127.0.0.1] mod_fcgid: read
> > > data timeout in 40 seconds
> > >
> > > [Sun Nov 11 01:40:24 2012] [error] [client 127.0.0.1] Premature end of
> > > script headers: access.scm
> > >
> > > [Sun Nov 11 01:40:24 2012] [warn] [client 127.0.0.1] mod_fcgid: user
> > > (null) access check failed, respond 500, URI /scm/api/access.scm
> > >
> > > [Sun Nov 11 01:40:26 2012] [debug] fcgid_pm_main.c(357): mod_fcgid:
> > > gracefully terminated 1 processes
> > >
> > > How can I diagnose the problem? I find it interesting that it works
> > > under mod_fastcgi but not mod_fcgid; I'm not sure whether that implies
> > > the problem is in mod_fcgid, however.
> > >
> > >
> > > Footnotes:
> > > [1] The script is written in Chicken Scheme, by the way.
> > >
> > >
> > > ---------------------------------------------------------------------

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> >
>
> --
> Born in Roswell... married an alien...
> http://emptyhammock.com/

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