Symptoms
- There was a dist-upgrade from Debian 8 to Debian 9 that caused 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.
/var/log/plesk/install/plesk-distupgrade.log
file:
apache2: Syntax error on line 146 of /etc/apache2/apache2.conf: Syntax error on line 2 of /etc/apache2/mods-enabled/proxy_fcgi.load: Cannot load /usr/lib/apache2/modules/mod_proxy_fcgi.so into server: /usr/lib/apache2/modules/mod_proxy_fcgi.so: undefined symbol: ap_proxy_check_connection
-
proxy
module is enabled andproxy_fcgi
module is disabled:# apachectl -M | grep -E ‘proxy_module|proxy_fcgi’
proxy_module (shared)
Cause
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
Resolution
Note: if direct SSH access to the server is not possible, contact server administrator for further assistance.
- Connect to the server via SSH;
- Remove libapache2-mod-proxy-psa package:
# dpkg -r –force-depends libapache2-mod-proxy-psa
-
Disable
proxy
module# a2dismod proxy
-
Start Apache:
# systemctl start apache2.service
-
Enable
proxy
andproxy_fcgi
modules.# a2enmod proxy
# a2enmod proxy_fcgi -
Restart Apache:
# systemctl restart apache2
Additional information
Apache fails to start: ndefined symbol: ap_unixd_setup_child