Location of http.conf

ps -ef | grep apache

will give the location of the instance of apache that is running:

root      1186     1  0 Aug04 ?        00:00:02 /usr/sbin/apache2 -k start
www-data  1430  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  1431  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  1432  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  1433  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  1434  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  3315  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
www-data  3499  1186  0 Aug04 ?        00:00:00 /usr/sbin/apache2 -k start
john      4818  4559  0 19:55 pts/1    00:00:00 grep --color=auto apache

In my case, that's actually a link, not the executable:

apache2 -> ../lib/apache2/mpm-prefork/apache2*

However,

/usr/sbin/apache2 -V

gives me:

Server version: Apache/2.2.22 (Ubuntu)
Server built:   Jul 22 2014 14:37:02
Server's Module Magic Number: 20051115:30
Server loaded:  APR 1.4.6, APR-Util 1.3.12
Compiled using: APR 1.4.6, APR-Util 1.3.12
Architecture:   32-bit
Server MPM:     Prefork
  threaded:     no
    forked:     yes (variable process count)
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=128
 -D HTTPD_ROOT="/etc/apache2"
 -D SUEXEC_BIN="/usr/lib/apache2/suexec"
 -D DEFAULT_PIDLOG="/var/run/apache2.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_LOCKFILE="/var/run/apache2/accept.lock"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="mime.types"
 -D SERVER_CONFIG_FILE="apache2.conf"

httpd.conf is therefore in /etc/apache2. It was empty to begin with.

Restart server

/etc/init.d/apache2 restart

Define Default Page(s)
in

/etc/apache2/mods-enabled/dir.conf

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Resources
Ubuntu Documentation > Ubuntu 10.04 > Ubuntu Server Guide > Web Servers > HTTPD - Apache2 Web Server