Updating Drupal Core using Drush

Log into your server through SSH, and change directories to your root Drupal installation directory which contains the sites folder.

cd /home/myuser/public_html/

Run the following command which will ask you to confirm you want to update the found Drupal installation, enter "y" to finish

drush pm-update

Example Output:

sh-4.1$ drush pm-update
 Name    Installed Version  Proposed version  Message
 Drupal  7.26               7.27              SECURITY UPDATE available


Update information last refreshed: Wed, 05/07/2014 - 04:32
Code updates will be made to drupal core.
WARNING:  Updating core will discard any modifications made to Drupal core files, most noteworthy among these are .htaccess and robots.txt.  If you have made any modifications to these files, please back them up before updating so that you can re-create your modifications in the updated version of the file.
Note: Updating core can potentially break your site. It is NOT recommended to update production sites without prior testing.

Do you really want to continue? (y/n): y
Project drupal was updated successfully. Installed version is now 7.27.
Backups were saved into the directory /home/myuser/drush-backups/mysite/20140507150101/drupal.                    [ok]
No database updates required                                                                                      [success]
'all' cache was cleared.                                                                                          [success]
Finished performing updates.                                                                                      [ok]

Installing Drupal's Drush

Installing Drush on CentOS using Yum and PEAR

Check if PEAR is on the server:

pear version

If PEAR is not on the server then install using yum:

yum install php-pear

Prepare PEAR

sudo pear channel-discover pear.drush.org

Install:

sudo pear install drush/drush