Nov 27

remove server info and PHP info from response header

Below is a comm http response header:

HTTP/1.1 200 OK
Date: Wed, 27 Nov 2013 01:18:27 GMT
Server: Apache/2.0.55 (Debian) PHP/5.1.2
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-Encoding: gzip
Vary: Accept-Encoding
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8

To keep your server from attack, you should hide all unnecessary information about your system.With apache web server,this was control by ServerTokens  and ServerSignature config directive.From apache manual,we find out  all available config value of ServerTokens and its sample out.

ServerTokens Prod[uctOnly]
Server sends (e.g.): Server: Apache
ServerTokens Major
Server sends (e.g.): Server: Apache/2
ServerTokens Minor
Server sends (e.g.): Server: Apache/2.0
ServerTokens Min[imal]
Server sends (e.g.): Server: Apache/2.0.41
ServerTokens OS
Server sends (e.g.): Server: Apache/2.0.41 (Unix)
ServerTokens Full (or not specified)
Server sends (e.g.): Server: Apache/2.0.41 (Unix) PHP/4.2.2 MyMod/1.2

Obviously, we should turn our config to ServerTokens Prod.

To stop apache from exposing info in related error page,we need to turn off ServerSignature.

ServerSignature off

To hide the php related information,locate your php config file, find or add expose_php.

expose_php off

Nov 17

linux – how to replace special string in multiple files

As an administrator, you will need to fix an error for all user.I found that there are some users use [NC] flag with -f,-d,-l in their RewriteCond directive in zen cart .htaccess file. This misconfiguration is not so critical but it will force the busy server stop  to write to disk and generate huge big error log.i can not just sent a  notice to all the related customers about fixing their error.you know the customer is the god.

i don’t want to correct all the .htaccess file one by one.So,first i need to locate all the file contain
RewriteCond %{REQUEST_FILENAME} !-f [NC]

The command below will list all the .htaccess file containing ‘!-f [NC]‘ from all users’ document root.
# grep -ril ‘\!-f \[NC\]‘ /home/*/www/.htaccess

Now,with the single command below, i will replace all ‘!-f [NC]‘ with ‘!-f‘ in all related .htaccess files found.
#sed -i ‘s/\!-f \[NC\]/\!-f/g’ `grep -ril ‘\!-f \[NC\]‘ /home/*/www/.htaccess`

 

Nov 16

Apache – RewriteCond: NoCase option for non-regex pattern xx is not supported

we got lots of ‘NoCase option not supported’ warning like below from our apache server error log

[Fri Nov 15 20:46:14 2013] [warn] RewriteCond: NoCase option for non-regex pattern ‘-f’ is not supported and will be ignored.

As you may have guessed the problem is with your rewrite rule and one or more lines RewriteCond in your .htaccess file. From the mod_rewrite documentation,i found this

‘nocase|NC’ (no case)
This makes the test case-insensitive – differences between ‘A-Z’ and ‘a-z’ are ignored, both in the expanded TestString and the CondPattern. This flag is effective only for comparisons between TestString and CondPattern. It has no effect on filesystem and subrequest checks.

Pay attention to the last sentence It has no effect on filesystem and subrequest checks. this means that ‘nocase|NC’  is no need when you use ‘-d’ (directory) ‘-f’ (regular file) and ‘-l’ (symbolic link)  in your code pattern in the RewriteCond directive. they will just be ignored.

Unfortunately it is not explicitely written but these CondPatterns will only work in case sensitive mode when it contains filesystem related flags(-d,-f,-l).so keep in minds that you can not test insensitive mode in linux server.This means

If there is a file name A.php in domain(abcdomain.com) root it can be reached via http://www.abcdomain.com/A.php but not http://www.abcdomain.com/a.php

Someone may find that the warning messages still showing up that the waring show up in the error log file after the removed the NC flag.i thought it was because the error log was global error log,so the warning messages will continue showing up before you fix all website on the server.