~ubuntu-branches/ubuntu/natty/apache2/natty-security

Contents
========

	Apache2 Configuration under Debian GNU/Linux
		Files and Directories in /etc/apache2
		Tools

	Using mod_disk_cache

	SSL
		Enabling SSL
		Creating self-signed certificates
		SSL workaround for MSIE

	Suexec
	
	Documentation

	Upgrades

	Common Problems


Apache2 Configuration under Debian GNU/Linux
============================================

Debian's default Apache2 installation attempts to make adding and
removing modules, virtual hosts, and extra configuration directives as
flexible as possible, in order to make automating the changes and
administering the server as easy as possible.

Please be aware that this layout is quite different from the standard
Apache configuration. Due to the use of environment variables, apache2
needs to be started/stopped with /etc/init.d/apache2 or apache2ctl. 
Calling /usr/bin/apache2 directly will not work with the default
configuration. To call apache2 with specific command line arguments,
just call apache2ctl with the same arguments.

Files and Directories in /etc/apache2:
-------------------------------------

apache2.conf

	This is the main configuration file.

envvars

	This contains environment variables that may be used in the
	configuration. Some settings, like user and pid file, need to
	go in here so that other scripts can use them. It can also
	be used to change some default settings used by apache2ctl.
	Here is also the default LANG=C setting that can be changed
	to a different language.

conf.d/

	Files in this directory are included by this line in
	apache2.conf:

	# Include generic snippets of statements
	Include /etc/apache2/conf.d

	This is a good place to add additional configuration
	directives. Packages should not use configuration
	files that start with 'local-' or end with '.local'.
	The local administrator can use these filenames to make
	sure that there are no conflicts with files provided by
	packages.

	If the local administrator is not comfortable with packages
	activating their config files by default, it is possible
	to change the 'Include /etc/apache2/conf.d/' in apache2.conf
	into 'Include /etc/apache2/conf.d.enabled/' and create that
	directory. He can then put symlinks to the files in conf.d
	which he wants to enable into conf.d.enabled.

httpd.conf

	Empty file.

magic

	Patterns for mod_mime_magic. This is not compatible with the format
	used by current versions of the file/libmagic packages.

mods-available/

	This directory contains a series of .load and .conf files.
	The .load files contain the Apache configuration directive
	necessary to load the module in question.  The respective
	.conf files contain configuration directives necessary to
	utilize the module in question.

mods-enabled/

	To actually enable a module for Apache2, it is necessary to
	create a symlink in this directory to the .load (and .conf, if
	it exists) files associated with the module in
	mods-available/.  For example:

	cgi.load -> /etc/apache2/mods-available/cgi.load

ports.conf

	Configuration directives for which ports and IP addresses to
	listen to.

sites-available/

	Like mods-available/, except it contains configuration
	directives for different virtual hosts that might be used with
	apache2.  Note that the hostname doesn't have to correspond
	exactly with the filename.  'default' is the default host.

sites-enabled/

	Similar in functionality to mods-enabled/, sites-enabled
	contains symlinks to sites in sites-available/ that the
	admnistrator wishes to enable.

	Apache uses the first VirtualHost that matches the IP/Port
	as default for named virtual hosts. Therefore the 'default'
	site is linked to '000-default' so that it will be read first.

	Example:
	dedasys -> /etc/apache2/sites-available/dedasys

The Include directive ignores files with names that

- do not begin with a letter or number
- contain a character that is neither letter nor number nor _-.
- contain .dpkg

Other files
-----------

For historical reasons, the pid file is in /var/run/apache2.pid and not in
/var/run/apache2/apache2.pid.

Tools
-----

a2enmod and a2dismod are available for enabling and disabling modules utilizing
the above configuration system.

a2ensite and a2dissite do essentially the same thing as the above tools, but
for sites rather than modules.

apxs2 -a/-A is modified to use a2enmod to activate newly installed modules.


Using mod_disk_cache
====================

To ensure that the disk cache does not grow indefinitely, htcacheclean is
started when mod_disk_cache is enabled. Both daemon and cron (daily) mode
are supported. The configuration (run mode, cache size, ...) is in
/etc/default/apache2 .

Normally, htcacheclean is automatically started and stopped by
/etc/init.d/apache2. However, if you change the state of mod_disk_cache or the
configuration of htcacheclean while apache2 is running, you may need to
manually start/stop htcacheclean with "/etc/init.d/apache2 start-htcacheclean"
or "/etc/init.d/apache2 stop-htcacheclean".


SSL
===

Enabling SSL
------------

To enable SSL, type (as user root):

	a2ensite default-ssl
	a2enmod ssl

If you want to use self-signed certificates, you should install the ssl-cert
package (see below). Otherwise, just adjust the SSLCertificateFile and
SSLCertificateKeyFile directives in /etc/apache2/sites-available/default-ssl to
point to your SSL certificate. Then restart apache:

	/etc/init.d/apache2 restart

The SSL key file should only be readable by root, the certificate file may be
globally readable. These files are read by the Apache parent process which runs
as root. Therefore it is not necessary to make the files readable by the
www-data user.

Creating self-signed certificates
---------------------------------

If you install the ssl-cert package, a self-signed certificate will be
automatically created using the hostname currently configured on your computer.
You can recreate that certificate (e.g. after you have changed /etc/hosts or
DNS to give the correct hostname) as user root with:

	make-ssl-cert generate-default-snakeoil --force-overwrite

To create more certificates with different host names, you can use

	make-ssl-cert /usr/share/ssl-cert/ssleay.cnf /path/to/cert-file.crt

This will ask you for the hostname and place both SSL key and certificate in
the file /path/to/cert-file.crt . Use this file with the SSLCertificateFile
directive in the Apache config (you don't need the SSLCertificateKeyFile in
this case as it also contains the key). The file /path/to/cert-file.crt should
only be readable by root. A good directory to use for the additional
certificates/keys is /etc/ssl/private .

SSL workaround for MSIE
-----------------------

The SSL workaround for MS Internet Explorer needs to be added to your SSL
VirtualHost section (it was previously in ssl.conf but caused keepalive to be
disabled even for non-SSL connections):

	BrowserMatch "MSIE [2-6]" \
		nokeepalive ssl-unclean-shutdown \
		downgrade-1.0 force-response-1.0
	BrowserMatch "MSIE [17-9]" ssl-unclean-shutdown

The default SSL virtual host in /etc/apache2/sites-available/default-ssl
already contains this workaround.


Suexec
======

Debian ships two version of the suexec helper program required by mod_suexec.
It is not installed by default, to avoid possible security issues. The package
apache2-suexec contains the standard version that works only with document root
/var/www, userdir suffix public_html, and Apache run user www-data. The package
apache2-suexec-custom contains a customizable version, that can be configured
with a config file to use different settings (like /srv/www as document root).
For more information see the suexec(8) man page in the apache2-suexec-custom
package.

Since apache2-suexec-custom has received less testing and might be slightly
slower, apache2-suexec is the recommended version unless you need the features
from apache2-suexec-custom.


Documentation
=============

The full Apache 2 documentation can be found on the web at

http://httpd.apache.org/docs/2.2/

or, if you have installed the apache2-doc package, in

/usr/share/doc/apache2-doc/manual/

or at

http://localhost/manual/

There is also a wiki that contains useful information:

http://wiki.apache.org/httpd/

Some hints about securing Apache 2 on Debian are available at

http://wiki.debian.org/Apache/Hardening


Upgrades
========

Changes in the Apache packages that require manual configuration adjustments
are announced in NEWS.Debian. Installing the apt-listchanges package is
recommended. It will display the relevant NEWS.Debian sections before
upgrades.


Multiple instances
==================

There is some support for running multiple instances of Apache2 on the same
machine. See /usr/share/doc/apache2.2-common/README.multiple-instances for more
information.


Common Problems
===============

1) Error message "Could not reliably determine the server's fully qualified 
domain name, using 127.0.0.1 for ServerName" during start

This can usually be ignored but it means that Apache httpd was unable to obtain
a fully-qualified hostname by doing a reverse lookup on your server's IP
address. You may want to add the fully-qualified hostname to /etc/hosts .
An alternative is to specify "ServerName 127.0.0.1" in the global server
context of the configuration, e.g. in /etc/apache2/conf.d/servername.local .

2) Error message "mod_rewrite: could not create rewrite_log_lock"

This probably means that there are some stale SYSV semaphores around. This
usually happens after apache2 has been killed with kill -9 (SIGKILL). You can
clean up the semaphores with:

	ipcs -s | grep www-data | awk ' { print $2 } ' | xargs ipcrm sem

3) Message "NameVirtualHost *:80 has no VirtualHosts" in error log

Probably the VirtualHost definitions have not been adjusted after the 
NameVirtualHost directive was changed in ports.conf. 
See /usr/share/doc/apache2.2-common/NEWS.Debian.gz

4) Message "File does not exist: /etc/apache2/htdocs" in error log

In most cases this means that no matching VirtualHost definition could be
found for an incoming request. Check that the target IP address/port and the
name in the Host: header of the request actually match one of the virtual
hosts.

5) Message "Couldn't create pollset in child; check user or system limits" in
  error log

On Linux kernels since 2.6.27.8, the value in

    /proc/sys/fs/epoll/max_user_instances

needs to be larger than

    for prefork/itk  MPM: 2 * MaxClients
    for worker/event MPM: MaxClients + MaxClients/ThreadsPerChild

It can be set on boot by adding a line like

        fs.epoll.max_user_instances=1024

to /etc/sysctl.conf.

There are several other error messages related to creating a pollset that can
appear for the same reason.

On the other hand, errors about to adding to a pollset are related to the
setting fs.epoll.max_user_watches. On most systems, max_user_watches should be
high enough by default.

6) Message "Server should be SSL-aware but has no certificate configured" in
   error log

Since 2.2.12, Apache is stricter about certain misconfigurations concerning
name based SSL virtual hosts. See NEWS.Debian.gz for more details.

7) Apache does not pass Authorization header to CGI scripts

This is intentional to avoid security holes. If you really want to change it,
you can use mod_rewrite:

	RewriteCond %{HTTP:Authorization} (.*)
	RewriteRule . - [env=HTTP_AUTHORIZATION:%1]

8) mod_dav is behaving strangely

In general, if you use mod_dav_fs, you need to disable multiviews and script
execution for that directory. For example:

    <Directory /var/www/dav>
        Dav on
        Options -MultiViews -ExecCGI
        SetHandler none
        <IfModule mod_php5.c>
            php_admin_value engine Off
        </IfModule>
    </Directory>

9) Message "apache2: bad user name ${APACHE_RUN_USER}" when starting apache2
   directly

Use apache2ctl (it accepts all options of apache2).

10) Apache is using a lot of memory and is not freeing it even when idle

By default, Apache will not give back unused memory but keep it around for
later use.

  * Tune StartServers, MaxRequestsPerChild, MinSpareThreads/MinSpareServers,
    MaxSpareThreads/MaxSpareServers in /etc/apache2/apache2.conf

  * If you are really starved for memory, try adding 'MaxMemFree 4' to your
    Apache configuration. This will reduce Apache's performance.
    Because of the way Apache's memory allocator interacts with glibc's malloc,
    higher values of MaxMemFree don't have much effect.