Ubuntu plugin installation commands

install curl extension

sudo apt-get install php5-curl
sudo apt-get install curl libcurl3 libcurl3-dev php5-curl

install xslt extension

sudo apt-get install php5-xsl

command restart apache

sudo /etc/init.d/apache2 force-reload

path of the php.ini file
/etc/php5/apache2/php.ini

Increase you memory_limit in php.ini files to 32 MB
if your host now allowed you to change the php.ini files then
open your settings.php in sites/default folder

make ini_set("memory_limit","32M");

to see all the process
$ kill -9 pid
$ ps -A

installing GD library for ubuntu
Here are the steps to remedy it. This will install a GD pre-compiled working version. It is a complete bundled (forked) GD libraries:

1. Adding 2 lines to your file /etc/apt/sources.lst
deb http://packages.dotdeb.org stable all
deb-src http://packages.dotdeb.org stable all

2. If not already done removing your current GD package and its configurations.

sudo apt-get remove php5-gd
sudo apt-get --purge remove

3. Updating your current apt-get list

apt-get update

4. Installing working GD package.
apt-get install php5-gd

It will complain about non-authenticated sources, just ignore, it will also update some additional php libs.

When prompt select keep_current modified php.ini

5. Restarting Apache
/etc/init.d/apache2 restart