第一步：

1]配置软件源

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

[upgrade]

name=upgrade

baseurl=http://dev.centos.org/centos/6/upg/x86_64/

enable=1

gpgcheck=0

[2]安装软件工具

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

[3]升级前检查潜在问题

# preupg

Preupg tool doesn't do the actual upgrade.

Please ensure you have backed up your system and/or data in the event of a failed upgrade

that would require a full re-install of the system from installation media.Do you want to continue? y/n

y

Gathering logs used by preupgrade assistant:

All installed packages : 01/10 ...finished (time 00:00s)

All changed files      : 02/10 ...finished (time 00:40s)

Changed config files   : 03/10 ...finished (time 00:00s)

All users              : 04/10 ...finished (time 00:00s)

All groups             : 05/10 ...finished (time 00:00s)

Service statuses       : 06/10 ...finished (time 00:00s)

All installed files    : 07/10 ...finished (time 00:01s)

All local files        : 08/10 ...finished (time 00:03s)

All executable files   : 09/10 ...finished (time 00:00s)

RedHat signed packages : 10/10 ...finished (time 00:00s)

Assessment of the system, running checks / SCE scripts:

001/100 ...done    (Configuration Files to Review)

002/100 ...done    (File Lists for Manual Migration)

003/100 ...done    (Bacula Backup Software)

004/100 ...done    (MySQL configuration)

005/100 ...done    (Migration of the MySQL data stack)

006/100 ...done    (General changes in default MySQL implementation)

007/100 ...done    (PostgreSQL upgrade content)

Assessment finished (time 00:00s)

Result table with checks and their results for main contents:

------------------------------------------------------------------------------------------

|System kickstart                                                        |notapplicable  |

|YUM                                                                     |notapplicable  |

|Check for usage of dangerous range of UID/GIDs                          |notapplicable  |

|Incorrect usage of reserved UID/GIDs                                    |notapplicable  |

|NIS ypbind config files back-up                                         |notapplicable  |

|NIS Makefile back-up                                                    |notapplicable  |

|NIS server maps check                                                   |notapplicable  |

|NIS server MAXUID and MAXGID limits check                               |notapplicable  |

|NIS server config file back-up                                          |notapplicable  |

------------------------------------------------------------------------------------------

Tarball with results is stored here /root/preupgrade-results/preupg_results-140716022514.tar.gz .

The latest assessment is stored in directory /root/preupgrade .

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 .

[4]开始升级

# rpm --import http://centos.excellmedia.net/7.0.1406/os/x86_64/RPM-GPG-KEY-CentOS-7

正常的运行以上命令可以升级完成；

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

这强制的就显得有点不友好了，生产环境慎用；

更新到这一步：

setting up repos...

.treeinfo                                                                                                | 1.1 kB     00:00

getting boot images...

vmlinuz-redhat-upgrade-tool                                                                              | 4.7 MB     01:38

initramfs-redhat-upgrade-tool.img                                                                        |  32 MB     14:45

setting up update...

finding updates 100% [=====================================================================================================]

(1/272): acl-2.2.51-12.el7.x86_64.rpm                                                                    |  81 kB     00:00

(2/272): attr-2.4.46-12.el7.x86_64.rpm                                                                   |  66 kB     00:00

(3/272): audit-2.3.3-4.el7.x86_64.rpm                                                                    | 223 kB     00:01

(4/272): audit-libs-2.3.3-4.el7.x86_64.rpm                                                               |  77 kB     00:00

(5/272): authconfig-6.2.8-8.el7.x86_64.rpm                                                               | 399 kB     00:08

(6/272): basesystem-10.0-7.el7.centos.noarch.rpm                                                         | 5.0 kB     00:00

(7/272): bash-4.2.45-5.el7.x86_64.rpm                                                                    | 1.0 MB     00:17

(270/272): yum-plugin-fastestmirror-1.1.31-24.el7.noarch.rpm                                             |  28 kB     00:03

(271/272): zlib-1.2.7-13.el7.x86_64.rpm                                                                  |  89 kB     00:06

(272/272): zlib-devel-1.2.7-13.el7.x86_64.rpm                                                            |  49 kB     00:01

setting up system for upgrade

Finished. Reboot to start upgrade.

# reboot

[5]升级完成:

# cat /etc/redhat-release 

CentOS Linux release 7.0.1406 (Core)