环境是阿里云的CentOS7.0，更新了yum源（更新yum源请参考https://help.aliyun.com/knowledge_detail/5974184.html）之后先是尝试安装了MySQL5.7，但是折腾了一下午没有解决初始密码的问题。项目进度很紧，索性推倒重来上MySQL5.5。今天总算装好了。以下是基本步骤：(可以跳过卸载这一步)
1.卸载原mysql
1 #列出安装的mysql
2 rpm -qa | grep mysql
1 #干掉列出的items
2 rpm -e [item1]
3 rpm -e [item2]
4 rpm -e [item3]
由于5.7基于mariadb，所以还必须卸掉它：
1 #列出
2 rpm -qa | grep mariadb
1 #卸载
2 rpm -e mariadb-devel-5.5.44-2.el7.centos.x86_64
3 rpm -e mariadb-libs-5.5.44-2.el7.centos.x86_64
删除相关文件夹
find / -name mysql
#将列出的文件夹一一删除。
2.下载MySQL（RPM Bundle）
地址不一定存在，所以去官网复制一下比较保险，官网找到MySQL Community Server，platform我选的是Linux-Generic.
注意要选这个RPM Bundle，其他版本是编译安装的，只有带RPM Bundle的是RPM合集包。点Dowlaod去下一页：
复制这个 No thanks 的链接地址就是我们需要的链接地址。
3.安装MySQL5.5.48
回到linux,使用刚才复制的地址：
mkdir /usr/local/src/mysql
cd /usr/local/src/mysql
wget http://dev.mysql.com/get/Downloads/MySQL-5.5/MySQL-5.5.48-1.linux2.6.x86_64.rpm-bundle.tar
下载完毕，tar -xf MySQL-5.5.48-1.linux2.6.x86_64.rpm-bundle.tar
ls 应该能看到如下：
需要依次安装 client devel server （community-release我也装了）
安装的时候有几次报错如下：
error: Failed dependencies:
libc.so.6 is needed by MySQL-client-5.5.48-1.linux2.6.i386
libc.so.6(GLIBC_2.0) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libc.so.6(GLIBC_2.1) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libc.so.6(GLIBC_2.1.3) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libc.so.6(GLIBC_2.2) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libc.so.6(GLIBC_2.3) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libdl.so.2 is needed by MySQL-client-5.5.48-1.linux2.6.i386
libdl.so.2(GLIBC_2.0) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libdl.so.2(GLIBC_2.1) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libm.so.6 is needed by MySQL-client-5.5.48-1.linux2.6.i386
libm.so.6(GLIBC_2.0) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libncurses.so.5 is needed by MySQL-client-5.5.48-1.linux2.6.i386
libpthread.so.0 is needed by MySQL-client-5.5.48-1.linux2.6.i386
libpthread.so.0(GLIBC_2.0) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libpthread.so.0(GLIBC_2.1) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libpthread.so.0(GLIBC_2.2) is needed by MySQL-client-5.5.48-1.linux2.6.i386
libpthread.so.0(GLIBC_2.3.2) is needed by MySQL-client-5.5.48-1.linux2.6.i386
librt.so.1 is needed by MySQL-client-5.5.48-1.linux2.6.i386
librt.so.1(GLIBC_2.2) is needed by MySQL-client-5.5.48-1.linux2.6.i386
error: Failed dependencies:
libaio.so.1 is needed by MySQL-server-5.5.48-1.linux2.6.i386
libaio.so.1(LIBAIO_0.1) is needed by MySQL-server-5.5.48-1.linux2.6.i386
libaio.so.1(LIBAIO_0.4) is needed by MySQL-server-5.5.48-1.linux2.6.i386
整理了一下，基本上安装以下几个依赖（如果yum源没有这些包，可以尝试更新一下https://help.aliyun.com/knowledge_detail/5974184.html)
1 yum -y install glibc.i686
2 yum -y install libncurses.so.5
3 yum -y install libaio.so.1
4 yum -y install libz.so.1
安装完毕再次尝试安装MySQL5.5，这次没问题了：
1 rpm -ivh MySQL-server-5.5.48-1.linux2.6.i386.rpm
2 rpm -ivh MySQL-devel-5.5.48-1.linux2.6.i386.rpm
3 rpm -ivh MySQL-client-5.5.48-1.linux2.6.i386.rpm
4 rpm -ivh mysql57-community-release-el7-7.noarch.rpm
5 #以下并不必须
6 rpm -ivh MySQL-embedded-5.5.48-1.linux2.6.i386.rpm
7 rpm -ivh MySQL-shared-5.5.48-1.linux2.6.i386.rpm
8 rpm -ivh MySQL-shared-compat-5.5.48-1.linux2.6.i386.rpm
9 rpm -ivh MySQL-test-5.5.48-1.linux2.6.i386.rpm
启动：
service mysql start
这里我遇到一个问题，似乎是还有原来的mysql进程没有杀干净，我使用了ps -ef | grep mysql，然后kill -9 了列出的进程，就启动成功了。
测试：
perfect！！
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