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Emlyn Jones
emlynj at gmail.com
Mon Jun 26 13:29:02 EDT 2006
On 6/26/06, Emlyn Jones <emlynj at gmail.com> wrote: > On 6/26/06, Emlyn Jones <emlynj at gmail.com> wrote: > > On Monday 26 Jun 2006 01:13, Graham Dumpleton wrote: > > > Emlyn Jones wrote .. > > > > > > > Hello, > > > > I've got this simple piece of mod_python/psp; If I uncomment the > > > > foo=session line I get a seg fault. Has anyone seen this before and can > > > > direct me towards finding out what the problem is please? > > > > I'm running Apache/2.0.50, mod_python 3.2.8 and Python 2.4. > > > > I've confirmed that it isn't the known expat and mysql/php problems. > > > > > > > > <% > > > > #foo = session > > > > done_login = False > > > > if(form.has_key("username")): > > > > username = form["username"] > > > > password = form["password"] > > > > req.write("%s" % (username,)) > > > > %> > > > > > > What PSP does is that if it sees that the variable "session" is referenced > > > from inside of PSP code, then it will do what is necessary to create the > > > session, or if the session already exists, it will retrieve it from the > > > session database. > > > > > > Two problems could be occurring here. The first is that if this is > > > occurring on the very first time the session needs to be created, that the > > > session database it tries to use is corrupt in some way and therefore > > > crashing. The second is that the session already exists in the database, > > > but something was stored in the session object that probably shouldn't have > > > and when the session object is being restored, it is triggering some code > > > (possibly C code) which is then subsequently crashing. > > > > > > First thing you need to do is get out of PSP and write a simple handler > > > that creates a session object just to validate that sessions work and that > > > the session database is okay. Use a handler such as: > > > > > > from mod_python import Session > > > from mod_python import apache > > > > > > def handler(req): > > > session = Session.Session(req) > > > session['data'] = 1 > > > session.save() > > > req.content_type = 'text/plain' > > > req.write('hello') > > > return apache .OK > > > > > > If this dies, then there is possibly a problem with the session > > > database, or your Python DBM modules are stuffed somehow. You need to > > > work out what type of session database is being used. It will probably > > > be DBM database and it will be stored in "/tmp" as "/tmp/mp_sess.dbm". I > > > am guessing you aren't on Win32 as in that case an in memory session > > > database is being used and it would be almost impossible to crash. Which > > > is might be is dictated by the MPM which Apache was configured with. > > > > > > Assuming it is DBM, check who owns the database in "/tmp". The owner > > > should match the user that Apache runs as. If you have multiple versions > > > of Apache running and they run as different users, you could have problems > > > because of that. If it is the wrong user and you only have one Apache > > > instance, you could try deleting the database and restarting Apache. > > > If you have multiple versions of Apache running as different users, you > > > may have to use PythonOption to change location where session database > > > is stored. See documentation for mod_python. > > > > > > If this is all okay, may be what you are storing in the session object. > > > This is where you need to show your code as to what you are sticking in the > > > session object before we can really comment. Also read: > > > > > > http://www.dscpl.com.au/articles/modpython-005.html > > > > > > Graham > > > > Hi Graham, thanks for the reply and explanation. > > That simple handler does die. The dbm file in /tmp checks out ok, it's the > > correct user and I haven't actually managed to store anything in it yet. This > > is the first use of it; In fact, If I rename it (the dbm file) and restart > > apache it doesn't get recreated so I guess that leaves me with the python DBM > > modules. > > I'll have a dig around and see what I can come up with. > > I do vaguely remember a caffeine fuelled evening running into problems with > > sleepycat which sounds like it might be connected (maybe library versions?). > > Is there any extra debugging info I can turn on to point me in the right > > direction? Otherwise I suppose it's trying to test out the dbm stuff in a > > python shell first and take it from there. > > > > Cheers, > > Emlyn. > > > > _______________________________________________ > > Mod_python mailing list > > Mod_python at modpython.org > > http://mailman.modpython.org/mailman/listinfo/mod_python > > > Hello, > I'm not sure if I'm heading in the right direction here. > I can see from a python shell that the dbm module is using the > "Berkeley DB" library (dbm.library). > lsof -p <http pid> | grep dbm shows that it is linked to libgdbm.so.3.0.0. > I'm a little confused but could this be the root of my problems? > > Cheers, > Emlyn. > > /usr/lib/libgdbm.so.3.0.0 > Ok, now I'm really stuck. I've rebuilt a vanilla version of Python2.4 and recompiled Apache and mod_python. I then removed the existing dbm file in /tmp and restarted everything. Still get a seg fault when I try to use the session. No new dbm file has been created. Is there a way to make mod_python/psp use a FileSession instead of DBM? At least then I can confirm that it is some kind of dbm problem. Maybe there are some tests I can do from the shell to see if the dbm stuff is working in python (a simple test of creating a new db and saving stuff to it suggests that it is)? It's definitely not what I'm storing in the session, I can't get close to storing anything. Any more pointers would save what little hair I have left. Cheers, Emlyn.
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