The apache2 server frequently stops with the error below. When I manually (re)start the apache2 server, it starts okay.

The error messages in the apache2 log:
[Sat Jan 30 14:15:02.081221 2016] [mpm_prefork:notice] [pid 19521] AH00171: Graceful restart requested, doing restart
[Sat Jan 30 14:15:02.113546 2016] [:notice] [pid 19521] mod_python: Creating 8 session mutexes based on 150 max processes and 0 max threads.
[Sat Jan 30 14:15:02.113562 2016] [:notice] [pid 19521] mod_python: using mutex_directory /tmp
Fatal Python error: PyEval_SaveThread: NULL tstate
[Sat Jan 30 14:15:02.113634 2016] [core:notice] [pid 19521] AH00060: seg fault or similar nasty error detected in the parent process

Please let me know if anyone has an advice.

Thank you!