1，下载composer并执行

[root@localhost ~]# curl -sS https://getcomposer.org/installer | php
All settings correct for using Composer
Downloading 1.1.3...

Composer successfully installed to: /root/composer.phar
Use it: php composer.phar
[root@localhost ~]# 

2.把composer.phar移动到全局环境中

[root@localhost ~]# mv composer.phar /usr/local/bin/composer
[root@localhost ~]# composer -v
   ______
  / ____/___  ____ ___  ____  ____  ________  _____
 / /   / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__  )  __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
                    /_/
Composer version 1.1.3 2016-06-26 15:42:08