Python – Why does httpd seem to use a different version of python with the same executable

apache-2.4mod-wsgipythonvirtualenv

I am running Apache httpd 2.4.4 on a RedHat 5 machine. I am using Django and running through mod_wsgi. I have Python 2.4.3 installed in /usr/bin and Python 2.7.6 installed in /usr/local/bin and I want to use 2.7.6. I build the 2.7.6 from source and also built mod_wsgi-3.4.

I have created a virtualenv using 2.7.6 and from a command shell, python -V tells me it's using 2.7.6 (after doing a . virtpy/bin/activate). Running import sys; sys.version shows me 2.7.6 as well, and sys.executable shows me /www/sqla/virtpy/bin/python.

When I run it from httpd, I get problems loading libraries and when I look at sys.version, I see 2.7.3. The weird thing is that sys.executable still shows me /www/sqla/virtpy/bin/python, exactly the same one as I see from the command shell.

Specifically, when python tries to load _socket, I see this error from httpd:

ImportError: /www/sqla/virtpy/lib/python2.7/lib-dynload/_socket.so: undefined symbol: _PyInt_AsInt

If I try to import _socket from a command shell, no problem. I have . /www/sqla/virtpy/bin/activate in my /etc/sysconfig/httpd and have restarted Apache with that change.

How can the same executable give different versions of python? How can I convince it to use the right one?

Best Answer

Use the checks documented in the mod_wsgi documentation to validate that how your mod_wsgi was compiled is correct:

http://code.google.com/p/modwsgi/wiki/CheckingYourInstallation#Python_Shared_Library

Ensure that when doing this check that LD_LIBRARY_PATH is not set. Provide the output from ldd.

Also indicate whether you also have any Python 2.7 installation under /usr in addition to the one under /usr/local and specifically whether there is a Python 2.7 shared library under /usr/lib anywhere.

If you have used WSGIPythonHome directive in Apache configuration, say what you have set it to.

compiling python 2.7

./configure \
   --prefix=/usr/local \
   --enable-unicode=ucs4 \
   --enable-shared \
   LDFLAGS="-Wl,-rpath /usr/local/lib"

make && make altinstall

don't forget --enable-shared or you may have problems later on.

compiling mod_wsgi for python 2.7

https://code.google.com/p/modwsgi/wiki/InstallationIssues

since you did a make altinstall to install python2.7 you won't have a python-devel package to install; so you would need the mod_wsgi to refer to proper python.

./configure --with-python=/usr/local/bin/python2.7 
# then edit Makefile if you want to change DESTDIR
make && make install

... try to start httpd ...

Starting httpd: httpd: Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 2 of /etc/httpd/conf.d/wsgi.conf: Cannot load /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so into server: libpython2.7.so.1.0: cannot open shared object file: No such file or directory

Because we are not using the same python and we didn't link the module with any particular option to make it look in the correct place, it cannot find libpython2.7.so.1.0, we can change that by making libtool check the correct place.

# use LDFLAGS to tell libtool resulting lib needs to
# look for shared libs in /usr/local/lib too.
./configure \
   --with-python=/usr/local/bin/python2.7 \
   LDFLAGS="-R/usr/local/lib"
# then edit Makefile if you want to change DESTDIR
# e.g. DESTDIR = /opt/mod_wsgi2.7
make && make install

... try to start http again ...

Starting httpd: httpd: Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 2 of /etc/httpd/conf.d/wsgi.conf: Cannot load /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so into server: /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so: cannot open shared object file: Permission denied

That last error is because my system is running selinux and the file has the default context. A quick look at stackoverflow tells me it is an selinux issue.

fixing selinux context

# ls -Z /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so 
-rwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so

The fix is to use the correct context, which can be found on the original mod_wsgi module.

chcon --reference /etc/httpd/modules/mod_wsgi.so /opt/mod_wsgi2.7/usr/lib64/httpd/modules/mod_wsgi.so

Ubuntu – Recompiling python with SSL support on ubuntu

To link custom built software with library you need to have C headers installed. In ubuntu they are in -dev packages (libname-dev).

In your particular case you need to install libssl-dev (apt-get install libssl-dev) and

If you need SSL related functionality in standard library, then you should rebuild your python 2.7 installation.
For custom library SSL support, just rebuild libraries (pip uninstall && pip install)

Best Answer

Related Solutions

Python – Make mod_wsgi use python2.7.2 instead of python2.6

compiling python 2.7

compiling mod_wsgi for python 2.7

fixing selinux context

Ubuntu – Recompiling python with SSL support on ubuntu

Related Topic