A2enmod

a2enmod

is a shell script provided on Debian, and Debian-based Linux systems for quickly enabling extension modules of the Apache web server.

From the manual: a2enmod is a script that enables the specified module within the apache2 configuration. It does this by creating symlinks within /etc/apache2/mods-enabled. Likewise, a2dismod disables a module by removing those symlinks. It is not an error to enable a module which is already enabled, or to disable one which is already disabled.

Source

If you've never looked at a shell script before, and tutorials seem too basic, then here is an example of a more complete shell script:

/usr/sbin/a2enmod

#!/bin/sh -e

SYSCONFDIR='/etc/apache2'

if [ -z $1 ]; then
echo "Which module would you like to enable?"
echo -n "Your choices are: "
ls /etc/apache2/mods-available/*.load | \
sed -e "s,$SYSCONFDIR/mods-available/,,g" | sed -e 's/\.load$//g;' | xargs echo
echo -n "Module name? "
read MODNAME
else
MODNAME=$1
fi

#figure out if we are on a prefork or threaded mpm
if [ -x /usr/sbin/apache2 ]; then
PREFORK=`/usr/sbin/apache2 -l | grep -E 'prefork|itk' || true`
fi

if [ "$MODNAME" = "cgi" ] && [ -z $PREFORK ]; then
MODNAME="cgid"
echo "Your MPM seems to be threaded. Selecting cgid instead of cgi."
fi

if [ -e $SYSCONFDIR/mods-enabled/$MODNAME.load ]; then
echo "This module is already enabled!"
exit 0
fi

if ! [ -e $SYSCONFDIR/mods-available/$MODNAME.load ]; then
echo "This module does not exist!" >&2
exit 1
fi

DEPENDS=`grep "# Depends:" $SYSCONFDIR/mods-available/$MODNAME.load|cut -f2 -d:`
if [ ! -z "$DEPENDS" ]; then
for i in $DEPENDS; do
echo "Enabling $i as a dependency"
/usr/sbin/a2enmod "$i";
done
fi

Enabling a Module

If you don't know the exact name of the module you want to enable, you can invoke a2enmod without any arguments and it will output a list of the modules available on your host.

sudo a2enmod
Your choices are: actions alias asis auth_basic auth_digest authn_alias authn_anon authn_dbd authn_dbm authn_default authn_file authnz_ldap authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cern_meta cgi cgid charset_lite dav dav_fs dav_lock dav_svn dbd deflate dir disk_cache dump_io env expires ext_filter file_cache filter headers ident imagemap include info ldap log_forensic mem_cache mime mime_magic negotiation php5 proxy proxy_ajp proxy_balancer proxy_connect proxy_ftp proxy_http rewrite setenvif speling ssl status substitute suexec unique_id userdir usertrack version vhost_alias
Which module(s) do you want to enable (wildcards ok)?

Press 'Enter' to simply exit the script without making a selection.

If you do supply an argument (module name) to a2enmod, then the script will enable the module for you and give you some additional instructions to restart Apache

Disabling a Module

Similarly, modules can be disabled by using a2dismod