因为版本过低而导致composer服务器安装扩展失败怎么呢？下面由composer教程栏目给大家介绍其升级过程！
ps : 服务器 配置
Linux VM-0-9-ubuntu 4.4.0-91-generic #114-Ubuntu SMP Tue Aug 8 11:56:56 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
1. 失败经历
安装 easyswoole 的过程中，发现无法通过 composer 安装
报错信息如下：
ubuntu@VM-0-9-ubuntu:~/demo/easyswoole$ composer require easyswoole/easyswoole=3.x
./composer.json has been created
Loading composer repositories with package information
Updating dependencies (including require-dev)
Installation failed, deleting ./composer.json.
[ErrorException]
"continue" targeting switch is equivalent to "break". Did you mean to use "continue 2"?
require [--dev] [--prefer-source] [--prefer-dist] [--no-plugins] [--no-progress] [--no-update] [--update-no-dev] [--update-with-dependencies] [--ignore-platform-reqs] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--] [].. google 一下，没有对应的错误信息。 想着先查看一下 composer 版本
发现 ： composer 版本过低，就顺便升级composer 升级了再说。
ubuntu@VM-0-9-ubuntu:~/demo/easyswoole$ composer -V Composer version @package_branch_alias_version@ (1.0.0-beta2) 2016-03-27 16:00:34
升级的过程中发现，升级失败。 老版本的 composer 不能自动升级
ubuntu@VM-0-9-ubuntu:~$ composer self-update
[InvalidArgumentException]
Command "self-update" is not defined.看来是 composer 包太低，都没有自动升级的功能
2. 下载新的 composer 包
1. 新增最新的composer
wget https://dl.laravel-china.org/composer.phar -O /usr/local/bin/composer sudo chmod a+x /usr/local/bin/composer
然后把脚本 覆盖到原来的 （通过软链）
2. 查看原来的位置
sudo mv /usr/bin/composer /tmp/ sudo ln -s /usr/local/bin/composer /usr/bin/composer ubuntu@VM-0-9-ubuntu:~$ composer -V Composer version 1.8.5 2019-04-09 17:46:47
3. 安装
使用 composer 安装项目
