CentOS6升级到CentOS7

前提

• 只有独立服务器，PC，本地虚拟机，XEN,KVM架构的VPS才能升级成功，OpenVZ架构的VPS无法升级，望周知。
• 所有命令均在root下执行！

准备工作

vim /etc/yum.repos.d/upgrade.repo

[upgrade]
name=upgrade
baseurl=http://dev.centos.org/centos/6/upg/x86_64/
enabled=1
gpgcheck=0

接下来安装官方辅助工具：

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

安装好上述工具后，执行如下命令：

preupg

看到如下截图：

输入y，即可开始升级准备工作，接下来会看到如下画面（需等待几分钟到十几分钟，工具需要扫描所有文件）

Gathering logs used by preupgrade assistant:
All installed packages : 01/11 ...finished (time 00:00s)
All changed files      : 02/11 ...finished (time 01:51s)
Changed config files   : 03/11 ...finished (time 00:00s)
All users              : 04/11 ...finished (time 00:00s)
All groups             : 05/11 ...finished (time 00:00s)
Service statuses       : 06/11 ...finished (time 00:00s)
All installed files    : 07/11 ...finished (time 00:01s)
All local files        : 08/11 ...finished (time 00:10s)
All executable files   : 09/11 ...finished (time 00:01s)
RedHat signed packages : 10/11 ...finished (time 00:00s)
CentOS signed packages : 11/11 ...finished (time 00:00s)
Assessment of the system, running checks / SCE scripts:
001/095 ...done    (Configuration Files to Review)
002/095 ...done    (File Lists for Manual Migration)
003/095 ...done    (Bacula Backup Software)
004/095 ...done    (MySQL configuration)
...
093/095 ...done    (NIS server maps check)
094/095 ...done    (NIS server MAXUID and MAXGID limits check)
095/095 ...done    (NIS server config file back-up)
...
Tarball with results is stored here /root/preupgrade-results/preupg_results-140731025106.tar.gz .
The latest assessment is stored in directory /root/preupgrade .
Summary information:
We found some potential in-place upgrade risks.
Read the file /root/preupgrade/result.html for more details.
Upload results to UI by command:
e.g. preupg -u http://127.0.0.1:8099/submit/ -r /root/preupgrade-results/preupg_results-*.tar.gz .

上面是准备工作，接下来正式开始升级工作。

升级开始

导入CentOS7的KEY

rpm --import https://mirrors.ustc.edu.cn/centos/7/os/x86_64/RPM-GPG-KEY-CentOS-7

运行升级工具

redhat-upgrade-tool --network 7.0 --instrepo https://mirrors.ustc.edu.cn/centos/7/os/x86_64/

如果提示如下：

setting up repos...
.treeinfo                                                                                                                                        preupgrade-assistant has not been run.
To perform this upgrade, either run preupg or run redhat-upgrade-tool --force

那么就强制升级

redhat-upgrade-tool --network 7.0 --force --instrepo http://centos.excellmedia.net/7.0.1406/os/x86_64/

接下来跟普通的update差不多，看到下面内容时，表示升级所需的软件包都下载完毕了。

rpm transaction 100%[==================================================================================]
rpm install 100% [=====================================================================================]
setting up system for upgrade
Finished. Reboot to start upgrade.

接下来就重启系统

reboot

接下来可以打开主机上提供的远程管理工具，vnc之类的，就可以看到如下界面了

基本上跟系统update差不多

完成之后就看到新的系统登录界面啦

接下来验证下：

cat /etc/redhat-release
CentOS Linux release 7.0.1406 (Core)

完事！

不过，升级有风险，注意备份数据！！切记！！