Posts Tagged ‘unix servers’

Using rsync to copy / synchronize files or backups between Linux / BSD / Unix servers

Monday, November 21st, 2011

Rsync and Rsync over ssh logo picture

Many of us have already taken advantage of the powerful Rsync proggie, however I'm quite sure there are still people who never used rsync to transfer files between servers.. That's why I came with this small post to possibly introduce rsync to my blog readers.
Why Rsync and not Scp or SFTP? Well Rsync is designed from the start for large files transfer and optimized to do the file copying job really efficient. Some tests with scp against rsync will clearly show rsync's superiority.
Rsync is also handy to contiue copying of half copied files or backups and thus in many cases saves bandwidth and machine hdd i/o operations.

The most simple way to use rsync is:

server:~# rsync -avz -e ssh remoteuser@remotehost:/remote/directory /local/directory/

Where remoteuser@remotehost — is the the username and hostname of remote server to copy files to.
/remote/directory — is the directory where the rsync copied files should be stored
/local/directory — is the local directory from which files will be copied to remote directory

If not a preliminary passwordless ssh key (RSA / DSA) authentication is configured on remote server, the above command will prompt for a password otherwise the rsync will start doing the transfer.

If one needs to have a RSA or DSA (public / private key) passwordless SSH key authentication , a RSA key first should be generated and copied over to the remote server, like so:

server:~# ssh-keygen -t dsa
server:~# ssh-copy-id -i ~/.ssh/ root@remotehost

That's all folks, enjoy rsyncing 😉

Howto check if mod_rewrite is installed and loaded in Apache 2.x and serving directories correctly

Wednesday, February 10th, 2010

During my professional experience as a system administrator, it was a common misfortune in newly
configured unix servers mod_rewrite not to be serving .htaccess files.
Everytime I had to fix issue in which mod_rewrite was not working I loosed a lot of my precious time
The same story happened once again I had to check why mod_rewrite is not configured correctly and I cannot
apply some redirection rules in WordPress necessery for me
to exercise some SEO on my wordpress blog .
Therefore this time I decided to blog a step by step check on in order to:

1. Determine if mod_rewrite is installed & loaded correctly in Apache
2. Find out if mod_rewrite is configured to serve .htaccess files correctly
Going through this two scenarios I would be able to determine why I cannot get wordpress SEO optimization
mod_rewrite redirection rules to work as they should.
Okay, so let’s go through the two scenarios:

1. Here is a tiny script in PHP to determine if mod_rewrite is installed and loaded in Apache correctly
To use the script save it somewhere in your Domain document root with a .php extension
Here is the code of the script as well:

< ?phpprint_r(apache_get_modules());?>

If your mod_rewrite module is configured correctly you’ll see it in the php array containing
all your apache loaded modules.

Without PHP from the shell in order to get installed Apache modules on Linux, the following command applies:

apache2ctl -t -D DUMP_MODULES

For apache 2.2.x
httpd (or apache.exe) -M will show static and shared modules loaded via LoadModule.
httpd -l will show only static (compiled in) modules

For apache 2.0.x
httpd (apache.exe) -l is available but -M is not.
You will need to manually check the LoadModule directives and the files.

2. Now we continue, further on with another script that has to be installed somewhere in Apache’s DocumentRoot
I decided to install it in a directory /test/ so in my case it’s installed in
Here is a link to the script you need to find out if mod_rewrite is configured to serve .htaccess files for your preferred domain name’s DocumentRoot.

Now save this file and again make sure it has a .php extension.

Now you need to create an .htaccess file in the directory where you have rewrite.php file stored.
The content of the .htaccess file should be the following:

RewriteEngine OnRewriteOptions InheritRewriteRule ^link([^/]*).html$ rewrite.php?link=$1 [L]

Make sure the permissions of the .htaccess are correct, for example the file should have at least read
permissions for your webserver.
So let’s execute:

chmod a+r .htaccess to ensure the newly created file has proper permissions
So let’s check if mod_rewrite is enabled for my domain DocumentRoot by visiting:
this link
Hopefully if all is okay you’ll see:
Congratulations!! You are using Apache mod_rewrite whenever you press the TEST2 link
on the upmentioned webpage.

In case if you get a 404 error message, then most probably you don’t have mod_rewrite configured
to serve .htaccess files for your domain.
This often happens because of missing:
AllowOverride All in your main Directory directives in your webserver configuration file.
In my case I had a problem where mod_rewrite rules were not red from the .htaccess file:
To solve my issue I had to change:

Directory /
AllowOverride None
Order Deny,Allow
Deny from all
in my httpd.conf to

Directory /
AllowOverride All
Order Deny,Allow
Deny from all

So well, That’s all Folks!