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Jim Gallacher
jpg at jgassociates.ca
Mon Jun 26 14:12:27 EDT 2006
Emlyn Jones wrote: > 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. To use FileSession rather than the default DbmSession use: PythonOption session FileSession Jim
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