Bug#301305: apache2-common: APR support for shmem appears nonfunctional on 2.2 kernels

[Daniel Freedman <freedman@physics.cornell.edu>]

Package: apache2-common
Severity: normal

Hi,

It appears that the Debian APR has some difficulty with shmem on 2.2
kernels.  I perform the following configuration of Apache2 (debian
testing package: 2.0.53-5) on a given machine with everything
identical except for the difference of kernel (between official Debian
2.2.19 package and 2.4.27 package).  It works perfectly with 2.4.27
and fails repeatedly as below with 2.2.19.  During discussions with a
RedHat engineer through dev@httpd.apache.org list, it appears that a
similar shmem configuration is known to work with them on 2.2 kernels.  

The failure is that apache2 won't start if I include the following
line in my 'apache2-modssl.conf' file:

SSLSessionCache shmcb:/var/log/apache2/scache(512000)

I get the following error in my logs:
  [error] Cannot allocate shared memory: (22)Invalid argument
  
At first glance, bug #270524 might appear similar as it also deals
with a failure to allocate shared memory, but it that case the cache
file named in Apache's "SSLSessionCache" already exists.  In those
cases (generally from unclean shutdowns) it appeared that the solution
was easy: just manually delete the file.
  
In my case, the file doesn't exist, and I'm getting the "Invalid
argument" error.  Note also, that I've properly installed the Debian
libmm13 package, which appears to be necessary for properly
functioning shmcb, even though this doesn't appear to be widely
documented.

I solved my own problem by using the 2.4.27 kernel, but thought it
possibly should be documented and examined for others who need to stay
with 2.2.

Take care,
Daniel

-- 
Daniel A. Freedman <freedman@physics.cornell.edu>, Graduate Fellow
  Electronic Structure Calculations, LASSP, Cornell University