Recipe 3.2 Getting More Detailed Errors

Problem

You want more information in the error log in order to debug a problem.

Solution

Change (or add) the LogLevel line in your httpd.conf file. There are several possible arguments, which are enumerated below:

For example:

LogLevel Debug

Discussion

There are several hierarchical levels of error logging available, each identified by its own keyword. The default value of LogLevel is warn. Listed in descending order of importance, the possible values are:

emerg

Emergencies; web server is unusable

alert

Action must be taken immediately

crit

Critical conditions

error

Error conditions

warn

Warning conditions

notice

Normal but significant condition

info

Informational

debug

Debug-level messages

emerg results in the least information being recorded and debug in the most. However, at debug level a lot of information will probably be recorded that is unrelated to the issue you're investigating, so it's a good idea to revert to the previous setting when the problem is solved.

Even though the various logging levels are hierarchical in nature, one oddity is that notice level messages are always logged regardless of the setting of the LogLevel directive.

The severity levels are rather loosely defined and even more loosely applied. In other words, the severity at which a particular error condition gets logged is decided at the discretion of the developer who wrote the code—your opinion may differ.

Here are some sample messages of various severities:

[Thu Apr 18 01:37:40 2002] [alert] [client 64.152.75.26] /home/smith/public_html/
     test/.htaccess: Invalid command 'Test', perhaps mis-spelled or defined by a
     module not included in the server configuration
[Thu Apr 25 22:21:58 2002] [error] PHP Fatal error:  Call to undefined function:
     decode_url(  ) in /usr/apache/htdocs/foo.php on line 8
[Mon Apr 15 09:31:37 2002] [warn] pid file /usr/apache/logs/httpd.pid overwritten --
     Unclean shutdown of previous Apache run?
[Mon Apr 15 09:31:38 2002] [info] Server built: Apr 12 2002 09:14:06
[Mon Apr 15 09:31:38 2002] [notice] Accept mutex: sysvsem (Default: sysvsem)

These are fairly normal messages that you might encounter on a production web server. If you set the logging level to Debug, however, you might see many more messages of cryptic import, such as:

[Thu Mar 28 10:29:50 2002] [debug] proxy_cache.c(992): No CacheRoot, so no caching.
     Declining.
[Thu Mar 28 10:29:50 2002] [debug] proxy_http.c(540): Content-Type: text/html

These are exactly what they seem to be: debugging messages intended to help an Apache developer figure out what the proxy module is doing.

See Also

At the time of this writing, there is an effort underway to provide a dictionary of Apache error messages, what they mean, and what to do about the conditions they report, but it doesn't have anything concrete to show at this point. When it does, it should be announced at the Apache server developer site:

http://httpd.apache.org/dev/

It will be mentioned on this book's companion web site, as well:

http://Apache-Cookbook.Com/

In addition, see the detailed documentation of the LogLevel directive at the Apache site:

http://httpd.apache.org/docs/mod/core.html#loglevel