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How to switch from prefork mpm to worker mpm on ubuntu server?
how to roll back if there is any problem?

    root@myserver:~# apache2ctl -l
Compiled in modules:
root@myserver:~# aptitude search apache2-mpm-
p   apache2-mpm-event                                                      - Event driven model for Apache HTTPD
p   apache2-mpm-itk                                                        - multiuser MPM for Apache 2.2
p   apache2-mpm-perchild                                                   - Transitional package - please remove
i A apache2-mpm-prefork                                                    - Traditional model for Apache HTTPD
p   apache2-mpm-worker                                                     - High speed threaded model for Apache HTTPD

Thanks in advance.

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up vote 6 down vote accepted

As you will be changing your configuration it would be advisable to backup your current configuration befor your install:

$ cp -R /etc/apache2 ~/backup
$ sudo apt-get install apache2-mpm-worker

If you run into problems you can

$ sudo apt-get install apache2-mpm-prefork
$ cp -R ~/backup /etc/apache2
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On Ubuntu Server 14.04 I had to manually disable mpm-event and enable mpm-worker like this: sudo a2dismod mpm_event && sudo a2enmod mpm_worker && sudo service apache2 restart – dav.garcia May 19 at 6:46

Just install the package apache2-mpm-worker. If you have any problem with it, just install the package apache2-mpm-prefork again.

Also note that they are mutually exclusive. You can't install them at the same time.

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