After running
apt-get update && apt-get upgrade
on a Debian Wheezy server package apache2-mpm-prefork:amd64 was removed and package apache2-mpm-itk:amd64 installed instead. After this change in Apache worker, all Virtualhosts sites on the server stopped working, with the following error format in the logs:
[Mon Nov 21 09:57:41 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4012
[Mon Nov 21 09:57:55 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4019
[Mon Nov 21 09:57:58 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4025
[Mon Nov 21 09:58:23 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4058
[Mon Nov 21 09:59:23 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4092
[Mon Nov 21 10:00:47 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4737
[Mon Nov 21 10:01:47 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4770
[Mon Nov 21 10:02:23 2016] [emerg] [client xxx.xxx.xxx.xxx] (13)Permission denied: mod_fcgid: can't lock process table in pid 4813
PHP version was Wheezy default at the time, 5.4.45-0+deb7u5
Apache version was 2.2.22-13+deb7u7
ISPConfig hosting control panel was installed. PHP in ISPConfig was set as FastCGI.
After the upgrade, Apache could not start. I had to do a:
killall -9 apache2
and check the system ports to verify no process was still using port 80.
netstat -pnat | grep :80
showed no process, so Apache would start, but websites would not work.
After running
apt-get install apache2-mpm-prefork the prefork worker was installed, the newly installed itk worker was removed, and normal operation of the virtualhosts was resumed.