PROBLEM:

You try to execute from a shell some apache command like this:

# apache2 -t -D DUMP_MODULES

and you get the following error messages:

[Sun Nov 01 21:21:22.767389 2015] [core:warn] [pid 2923] AH00111: Config variable ${APACHE_LOCK_DIR} is not defined
[Sun Nov 01 21:21:22.767698 2015] [core:warn] [pid 2923] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Sun Nov 01 21:21:22.767936 2015] [core:warn] [pid 2923] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Sun Nov 01 21:21:22.768226 2015] [core:warn] [pid 2923] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Sun Nov 01 21:21:22.768530 2015] [core:warn] [pid 2923] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Nov 01 21:21:22.770286 2015] [core:warn] [pid 2923:tid 139821306185600] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Nov 01 21:21:22.770573 2015] [core:warn] [pid 2923:tid 139821306185600] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sun Nov 01 21:21:22.770772 2015] [core:warn] [pid 2923:tid 139821306185600] AH00111: Config variable ${APACHE_LOG_DIR} is not defined

CAUSE:

The user in your linux server does not have the apache2 environment variables properly set

SOLUTION:

Before executing any apache command, run this:

# source /etc/apache2/envvars

after this, all your apache commands will run successfully:

# apache2 -t -D DUMP_MODULES
Loaded Modules:
 core_module (static)
 so_module (static)
 watchdog_module (static)
 http_module (static)
 log_config_module (static)
 logio_module (static)
 version_module (static)
 unixd_module (static)
 access_compat_module (shared)
 alias_module (shared)
 auth_basic_module (shared)
 authn_core_module (shared)
 authn_file_module (shared)
 authz_core_module (shared)
 authz_host_module (shared)
 authz_user_module (shared)
 autoindex_module (shared)
 deflate_module (shared)
 dir_module (shared)
 env_module (shared)
 filter_module (shared)
 mime_module (shared)
 mpm_event_module (shared)
 negotiation_module (shared)
 setenvif_module (shared)
 socache_shmcb_module (shared)
 ssl_module (shared)
 status_module (shared)