• preupg
• http://vault.centos.org/RPM-GPG-KEY-CentOS-7">rpm —import http://vault.centos.org/RPM-GPG-KEY-CentOS-7
• http://vault.centos.org/7.2.1511/os/x86_64/">redhat-upgrade-tool —network 7.0 —instrepo http://vault.centos.org/7.2.1511/os/x86_64/

1. 添加yum源
   • vim /etc/yum.repos.d/upgrade.repo
   • [upgrade]
   • name=upgrade
   • baseurl=https://buildlogs.centos.org/centos/6/upg/x86_64/
   • enable=1
   • gpgcheck=0
2. 安装更新助手

• 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
  • yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm -y
  • yum install redhat-upgrade-tool preupgrade-assistant-contents -y

1. 升级前检查潜在问题

   • preupg

• 如下提示说明检查成功
  • Tarball with results is stored here /root/preupgrade-results/preupg_results-200812103424.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 .

1. 在线更新,在线更新会比较慢。可以先下载好镜像，进行本地更新。（只能升级到7.2之前的版本，7.2之后的boot images有差异）

   • rpm —import http://vault.centos.org/RPM-GPG-KEY-CentOS-7

   • redhat-upgrade-tool —network 7.0 —instrepo http://vault.centos.org/7.2.1511/os/x86_64/

2. 本地更新。
   • cd /tmp
   • wget https://mirrors.aliyun.com/centos/7.6.1810/isos/x86_64/CentOS-7-x86_64-DVD-1810.iso
   • centos-upgrade-tool-cli —iso=/tmp/CentOS-7-x86_64-DVD-1810.iso