Unable to start Apache after dist-upgrade on Plesk server

Unable to start Apache after dist-upgrade on Plesk server? We can help you.

This might be due to a package that exists on the server which remained from the older version.

As part of our Server Management Services, we assist our customers with several Plesk queries.

Today, let us see how our support techs fix this issue for our customers.

Unable to start Apache after dist-upgrade on Plesk server

The most common symptoms of this error include the following:

• A dist-upgrade from Debian 8 to Debian 9 can cause Apache2 to fail to start with the following error:

systemctl start apache2.service
Apr 24 09:39:24 hostname systemd[1]: Starting The Apache HTTP Server…
Apr 24 09:39:24 hostname apachectl[14512]: apache2: Syntax error on line 146 of /etc/apache2/apache2.conf: Syntax error on line 2 of /etc/apache2/mods-enabled/proxy_http.load: Cannot load /usr/lib/apache2/modules/mod_proxy_http.so into server: /usr/lib/apache2/modules/mod_proxy_http.so: undefined symbol: ap_proxy_check_connection
Apr 24 09:39:24 hostname apachectl[14512]: Action ‘start’ failed.

• The proxy module is enabled and the proxy_fcgi module is disabled:

apachectl -M | grep -E ‘proxy_module|proxy_fcgi’
proxy_module (shared)

We come across this error because the libapache2-mod-proxy-psa package exists on the server which remained from Debian 8:

dpkg -l libapache2-mod-proxy-psa
…
ii libapache2-mod-proxy-psa 2.4.10-debian8.0.17100418 amd64 Apache Module mod_proxy

Moving ahead, let us see how our Support Techs fix this issue once and for all.

How to Resolve this?

Suppose we cannot access the server by a direct SSH. In that case, our Support Techs recommend contacting the server administrator for further assistance.

Now, to fix the error, first, we connect to the server via SSH.

Then we remove the libapache2-mod-proxy-psa package:

dpkg -r –force-depends libapache2-mod-proxy-psa

After that, we go ahead and disable proxy module:

a2dismod proxy

Now we start Apache:

systemctl start apache2.service

Once done, we enable proxy and proxy_fcgi modules.

a2enmod proxy
# a2enmod proxy_fcgi

Finally, we restart Apache:

systemctl restart apache2

[In case you are still stuck with the restart, We are here to assist you]

Conclusion

In short, we saw how our Support Techs go about the restart error in Plesk.