sysadmin Tips » Tips

How to remove ^M from files

admin — Sat, 09 Jan 2010 15:12:57 +0000

When you transfered a file from Windows to Linux, you have ^ M characters that appear. This is due to the end line characters on Windows (\ r \ n) which are differents from Linux (\ n). There is some tips to remove them.

On vi, in command mode

:%s/[ctrl+v][ctrl+M]//

On emacs

M-%

From the shell, install tofrodos (on Debian):

$ dos2unix file.txt

$ unix2dos file.txt

The second command do the opposite.

Squid, HTTP authentification in accelerator mode

admin — Wed, 06 Jan 2010 19:12:23 +0000

When you use HTTP authentification, like in .htaccess with Apache, by default Squid doesn’t support this feature. You need to add an option, login=PASS, to the cache_peer to forward HTTP authentification requests to the backend servers:


cache_peer 172.16.1.1 parent 80 0 login=PASS no-query originserver weight=1

How to use differents cache_peer in Squid

admin — Wed, 06 Jan 2010 18:56:25 +0000

In accelerator mode, you can use the same Squid instance with differents cache_peer configuration using acl to choose where requests will go:

acl example2 dstdomain www.example2.com

cache_peer 172.16.1.1 parent 80 0 no-query originserver weight=1 name=clust1

cache_peer 172.16.1.2 parent 80 0 no-query originserver weight=1 name=clust2

cache_peer_access clust1 allow !example2

cache_peer_access clust2 allow example2


Request for the domain www.example2.com go to clust2 (172.16.1.2). However, request for others domain, like www.toto.com go to clust1 (172.16.1.1).



Rewrite rules for maintenance
admin — Mon, 21 Dec 2009 16:50:49 +0000
Here is the minimal (and the ultimate) rewrite rules to put a website in maintenance mode, works for Apache 2.x:
Options FollowSymLinks

AllowOverride All

RewriteEngine On

RewriteEngine on

RewriteCond %{REQUEST_URI} !\.gif$ [NC]

RewriteCond %{REQUEST_URI} !/maintenance.html$

RewriteRule $ /maintenance.html [R=307,L]
If you have anothers ressources in the maintenance.html page, like a css or js files, add more RewriteCond conditions:
RewriteCond %{REQUEST_URI} !\.css$ [NC]

RewriteCond %{REQUEST_URI} !\.js$ [NC]

RewriteCond %{REQUEST_URI} !\.png$ [NC]
Also, you can add a RewriteCond conditions to bypass the maintenance mode from a specific IP (or subnet …):
RewirteCond %{REMOTE_ADDR} !xxx\.xxx\.xxx\.xxx
Don’t forget to activate the rewrite module in Apache2, on a Debian:
# a2enmod rewrite

# apache2ctl configtest

# /etc/init.d/apache2 reload
Externals resources:

Apache 2.2 mod_rewrite