Chapter 14. Apache HTTP Server

197

other words, after a reverse lookup is performed, a forward lookup is performed on the result. At least

one of the IP addresses in the forward lookup must match the address from the first reverse lookup.

Generally, you should leave

HostnameLookups

set to

off

, because the DNS requests add a load to

your server and may slow it down. If your server is busy, the effects of

HostnameLookups

will be

noticeable.

HostnameLookups

are also an issue for the Internet as a whole. All of the individual connections

made to look up each hostname add up. Therefore, for your own Web server's benefit, as well as for

the good of the Internet as a whole, you should leave

HostnameLookups

set to

off

.

If you like to see the hostnames in your log files, consider running one of the many log analyzer tools

that perform the DNS lookups more efficiently and in bulk when you come to rotate your log files.

14.5.38.

ErrorLog

ErrorLog

names the file where server errors are logged. As this directive indicates, the error log file

for your Web server is

/var/log/httpd/error_log

.

The error log is a good place to look if your Web server generates any errors or fails, and you are not

sure what happened.

14.5.39.

LogLevel

LogLevel

sets how verbose the error messages in the error logs will be.

LogLevel

can be set (from

least verbose to most verbose) to

emerg

,

alert

,

crit

,

error

,

warn

,

notice

,

info

or

debug

. The

default

LogLevel

is

warn

.

14.5.40.

LogFormat

The

LogFormat

directives in your

httpd.conf

file set up a format for the messages in your access

log. The actual

LogFormat

used will depend on the settings given in the

CustomLog

directive (see

Section 14.5.41).

14.5.41.

CustomLog

CustomLog

identifies the log file and the log file format. In your Web server's default

configuration,

CustomLog

defines the log file in which accesses to your Web server are recorded:

/var/log/httpd/access_log

. You will need to know the location of this file if you want to

generate any access based server performance statistics for your Web server.

CustomLog

also sets the log file format to combined. The common logfile format looks like this:

remotehost rfc931 authuser [date] "request" status bytes referer user agent

remotehost

The remote hostname. If the hostname is not available from DNS, or if

HostnameLookups

is

set to

Off

, then

remotehost

will be the IP address of the remote host.

rfc931

Not used. You will see a

in the log file in its place.