Apache2 配置

A. Directory Indexes (from `mod_autoindex.c`)

When you access a directory and there is no default file found in this directory AND Apache Options Indexes is not enabled for this directory.

A.1. `DirectoryIndex` option example

DirectoryIndex index.html default.php welcome.php

A.2. `Options Indexes` option

If set, apache will list the directory content if no default file found (from the above option)

If none of the conditions above is satisfied

You will receive a 403 Forbidden

Recommendations

You should not allow directory listing unless REALLY needed.
Restrict the default index DirectoryIndex to the minimum.
If you want to modify, restrict the modification to the needed directory ONLY, for instance, use .htaccess files, or put your modification inside the <Directory /my/directory> directive

B. `Deny, Allow` directives (Apache 2.2)

Mentioned by @Radu, @Simon A. Eugster in the comments You request is denied, blacklisted or whitelisted by those directives.

I will not post a full explanation, but I think some examples may help you understand, in short remember this rule:

IF MATCHED BY BOTH, THE LAST IS WILL WIN

`Order Allow, Deny`

Deny will win if matched by both directives (even if an Allow directive is written after the Deny in the conf)

`Order Deny, Allow`

Allow will win if matched by both directives

Example 1

Order Allow, Deny
Allow from localhost mydomain.com

Only localhost and *.mydomain.com can access this, all other hosts are denied

Example 2

Order Allow, Deny
Deny from evil.com
Allow from safe.evil.com # <-- has no effect since this will be evaluated first

All requests are denied, the last line may trick you, but remember that if matched by both the last win rule (here Deny is the last), same as written:

Order Allow, Deny
Allow from safe.evil.com
Deny from evil.com # <-- will override the previous one

Example 4

Order Deny, Allow
Allow from site.com
Deny from untrusted.site.com # <-- has no effect since this will be matched by the above `Allow` directive

Requests are accepted from all hosts

Example 4: typical for public sites (allow unless blacklisted)

Order Allow, Deny
Allow from all
Deny from hacker1.com
Deny from hacker2.com

Example 5: typical for intranet and secure sites (deny unless whitelisted)

Order Deny, Allow
Deny from all
Allow from mypc.localdomain
Allow from managment.localdomain

C. `Require` directive (Apache 2.4)

Apache 2.4 use a new module called mod_authz_host

Require all granted => Allow all requests

Require all denied => Deny all requests

Require host safe.com => Only from safe.com are allowed

D. Files permissions

One thing that most people do it wrong is configuring files permissions,

The GOLDEN RULE is

STARTS WITH NO PERMISSION AND ADD AS PER YOUR NEED

In linux:

Directories should have the Execute permission
Files should have the Read permission
YES, you are right DO NOT ADD Execute permission for files

for instance, I use this script to setup the folders permissions

# setting permissions for /var/www/mysite.com

# read permission ONLY for the owner 
chmod -R /var/www/mysite.com 400 

# add execute for folders only
find /var/www/mysite.com -type d --exec chmod -R u+x {};

# allow file uploads 
chmod -R /var/www/mysite.com/public/uploads u+w

# allow log writing to this folder
chmod -R /var/www/mysite.com/logs/

A. Directory Indexes (from mod_autoindex.c)

A.1. DirectoryIndex option example

A.2. Options Indexes option