参考： http://blog.csdn.net/baidu_30000217/article/details/52942258 注意：composer并不是一个像apt-get 或者yum那样的包管理器，因为他们是全局的。而composer只是一个项目的依赖管理，它只会对当前目录的composer.json文件进行解析，然后将依赖的库安装到当前目录，除非手动指定全局安装到指定目录。
在自己用户的家目录下新建一个目录，来开始我们的测试，不要在/var/www目录或其子目录下创建这个项目
cqq@ubuntu:~/repos/test_composer$ ll total 12K drwxr-xr-x 2 cqq cqq 4.0K May 7 19:39 ./ drwxrwxr-x 12 cqq cqq 4.0K May 7 19:40 ../ -rw-r--r-- 1 cqq cqq 213 May 7 19:39 composer.json -rw-r--r-- 1 cqq cqq 0 May 7 19:28 function.php -rw-r--r-- 1 cqq cqq 0 May 7 19:27 index.php cqq@ubuntu:~/repos/test_composer$ composer install Cannot create cache directory /home/cqq/.composer/cache/repo/https---packagist.laravel-china.org/, or directory is not writable. Proceeding without cache Cannot create cache directory /home/cqq/.composer/cache/files/, or directory is not writable. Proceeding without cache Loading composer repositories with package information Updating dependencies (including require-dev) Package operations: 1 install, 0 updates, 0 removals - Installing phpmailer/phpmailer (v5.2.23): Downloading (100%) phpmailer/phpmailer suggests installing league/oauth2-google (Needed for Google XOAUTH2 authentication) Writing lock file Generating autoload files cqq@ubuntu:~/repos/test_composer$ ll total 20K drwxr-xr-x 3 cqq cqq 4.0K May 7 19:43 ./ drwxrwxr-x 12 cqq cqq 4.0K May 7 19:40 ../ -rw-r--r-- 1 cqq cqq 213 May 7 19:39 composer.json -rw-rw-r-- 1 cqq cqq 3.8K May 7 19:43 composer.lock -rw-r--r-- 1 cqq cqq 0 May 7 19:28 function.php -rw-r--r-- 1 cqq cqq 0 May 7 19:27 index.php drwxrwxr-x 4 cqq cqq 4.0K May 7 19:43 vendor/ cqq@ubuntu:~/repos/test_composer$ ll vendor/ total 20K drwxrwxr-x 4 cqq cqq 4.0K May 7 19:43 ./ drwxr-xr-x 3 cqq cqq 4.0K May 7 19:43 ../ -rw-rw-r-- 1 cqq cqq 178 May 7 19:43 autoload.php drwxrwxr-x 2 cqq cqq 4.0K May 7 19:43 composer/ drwxrwxr-x 3 cqq cqq 4.0K May 7 19:43 phpmailer/ cqq@ubuntu:~/repos/test_composer$ cat composer.json { "require": { "phpmailer/phpmailer": "*" }, "repositories": { "packagist": { "type": "composer", "url": "https://packagist.laravel-china.org" } } }