Drush 安装失败：您的需求无法解析为一组可安装的软件包答案

【问题标题】：Drush is failing to install: Your requirements could not be resolved to an installable set of packagesDrush 安装失败：您的需求无法解析为一组可安装的软件包
【发布时间】：2016-01-18 11:25:08
【问题描述】：

我已经根据https://getcomposer.org/doc/00-intro.md#globally 上的说明全局安装了 Composer，然后尝试安装 drush。不幸的是，drush 安装失败，出现以下错误：

composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for symfony/console v3.0.1 -> satisfiable by symfony/console[v3.0.1].
    - symfony/console v3.0.1 requires php >=5.5.9 -> your PHP version (5.4.16) or value of "config.platform.php" in composer.json does not satisfy that requirement.
  Problem 2
    - symfony/console v3.0.1 requires php >=5.5.9 -> your PHP version (5.4.16) or value of "config.platform.php" in composer.json does not satisfy that requirement.
    - psy/psysh v0.6.1 requires symfony/console ~2.3.10|^2.4.2|~3.0 -> satisfiable by symfony/console[v3.0.1].
    - Installation request for psy/psysh v0.6.1 -> satisfiable by psy/psysh[v0.6.1].

即使http://docs.drush.org/en/master/install 列出：

Drush 8 master  PHP 5.4.5+

我的环境是：

CentOS Linux release 7.2.1511 (Core) 
php -v
PHP 5.4.16 (cli) (built: Jun 23 2015 21:17:27) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies

不幸的是，我无法升级 PHP，因为我需要严格遵循 RHEL/CentOS 官方版本。

然后我决定尝试 Drush 7.x 分支，不幸的是它也给了：

composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Installation request for symfony/console v3.0.1 -> satisfiable by symfony/console[v3.0.1].
- symfony/console v3.0.1 requires php >=5.5.9 -> your PHP version (5.4.16) or value of "config.platform.php" in composer.json does not satisfy that requirement.
Problem 2
- symfony/console v3.0.1 requires php >=5.5.9 -> your PHP version (5.4.16) or value of "config.platform.php" in composer.json does not satisfy that requirement.
- psy/psysh v0.6.1 requires symfony/console ~2.3.10|^2.4.2|~3.0 -> satisfiable by symfony/console[v3.0.1].
- Installation request for psy/psysh v0.6.1 -> satisfiable by psy/psysh[v0.6.1].

在这种情况下我该怎么办？

【问题讨论】：

标签： drush

【解决方案1】：

你试过这样吗？为最新的 HEAD 版本执行此操作：

composer global require drush/drush:dev-master

如果您需要特定版本，例如最新版本 7，请执行此操作：

composer global require drush/drush:7.*

【讨论】：

是的，我做到了，但不幸的是它显示了上述依赖关系。我已经手动将 drush 命令的符号链接路径设为可执行，它现在对我有用，但是“官方”安装方式对我来说仍然失败。