最近公司领导突然问有没有做过系统升级，从centos6.5到centos7.x，我想这还不简单，直接配置下yum源，yum updata 完事，不过升级中可能会有不兼容问题等。自己做了个测试，centos6.5 升级到centos7.2 ，不能直接yum update。具体操作如下。

安装升级辅助工具

配置yum源

cat > /etc/yum.repos.d/upgrade.repo << EOF
[upgrade]
name=upgrade
baseurl=https://buildlogs.centos.org/centos/6/upg/x86_64/
enable=1
gpgcheck=0
EOF
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安装辅助工具

yum install redhat-upgrade-tool preupgrade-assistant-contents -y
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卸载openscap

由于centos 6.5自带的助手之一版本较高，所以需要卸载了装个更老的。

yum erase openscap -y
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移走系统自带的yum源

mkdir -p /etc/yum.repos.d/repo
mv /etc/yum.repos.d/CentOS-* /etc/yum.repos.d/repo/
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这样就可以使用之前配置好的yum源来安装openscap。

问题：是否可以先将系统自带的repo文件移走，直接使用我们配置好的安装？

　　--- 不能，因为安装辅助工具需要一些依赖包，如果移走系统自带的repo，将无法安装这些依赖。报错信息如下：

--> Processing Dependency: yum >= 3.2.29-43 for package: 1:redhat-upgrade-tool-0.7.22-3.el6.centos.noarch
--> Finished Dependency Resolution
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: pkgconfig(libpcre)
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1()(64bit)
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1(LIBXML2_1.0.11)(64bit)
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: libexslt.so.0()(64bit)
Error: Package: openscap-1.0.8-1.0.1.el6.centos.x86_64 (upgrade)
           Requires: libexslt.so.0()(64bit)
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1(LIBXML2_1.1.18)(64bit)
Error: Package: openscap-1.0.8-1.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1(LIBXML2_1.1.18)(64bit)
Error: Package: openscap-1.0.8-1.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1(LIBXML2_1.0.11)(64bit)
Error: Package: openscap-1.0.8-1.0.1.el6.centos.x86_64 (upgrade)
           Requires: libxslt.so.1()(64bit)
Error: Package: 1:redhat-upgrade-tool-0.7.22-3.el6.centos.noarch (upgrade)
           Requires: yum >= 3.2.29-43
           Installed: yum-3.2.29-40.el6.centos.noarch (@anaconda-CentOS-201311272149.x86_64/6.5)
               yum = 3.2.29-40.el6.centos
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: pkgconfig(libxslt)
Error: Package: preupgrade-assistant-1.0.2-36.0.1.el6.centos.x86_64 (upgrade)
           Requires: pkgconfig(libxml-2.0)
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest
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检查

升级前检查潜在问题，执行命令：

preupg -s CentOS6_7
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注意：是否可以直接升级，不检查？

　　--- 不建议，如果检查，执行升级命令后，会有提示，如下：

setting up repos...
upgradeiso                                                                                                                                 | 3.6 kB     00:00 ... 
upgradeiso/primary_db                                                                                                                      | 2.8 MB     00:00 ... 
Unable to open file /root/preupgrade/result.xml
preupgrade-assistant has not been run.
To perform this upgrade, either run preupg or run redhat-upgrade-tool --force
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升级

在线升级建议连接国外网，国内网下载速度实在太慢。离线升级比较快，建议使用iso镜像离线升级。

在线：

centos-upgrade-tool-cli --network 7 --instrepo=

离线：

centos-upgrade-tool-cli --iso=

验证

[root@localhost ~]# cat /etc/redhat-release 
CentOS Linux release 7.2.1511 (Core)
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