The installation directory "/root" is not writable - Error when install Drush i want to install drush on my server . 

I want to install drush-toolbox project globaly on my linux server box so all users can use it

My server: Cpanel , Litespeed , Cagefs , Cloudlinux (centos 6)

my drupal version 7.5x

I try this article CLick here and after run this command:

curl -sS https://getcomposer.org/installer | php


I get this error :
The installation directory "/root" is not writable

I run this command : chmod 640 /root and chmod 644 /root  but give same error (not writable)

Please help me.Is any guidance for me?
The composer method for installing drush works, but is outdated. Use the drush documentation for the right instructions: http://docs.drush.org/en/master/install/

# Download latest stable release using the code below or browse to github.com/drush-ops/drush/releases.
php -r "readfile('https://s3.amazonaws.com/files.drush.org/drush.phar');" &gt; drush
# Or use our upcoming release: php -r "readfile('https://s3.amazonaws.com/files.drush.org/drush-unstable.phar');" &gt; drush

# Test your install.
php drush core-status

# Make `drush` executable as a command from anywhere. Destination can be anywhere on $PATH.
chmod +x drush
sudo mv drush /usr/local/bin

# Optional. Enrich the bash startup file with completion and aliases.
drush init