CentOS 7.X升级至CentOS 8.2

1、安装dnf

CentOS 8开始使用dnf作为包管理器替代yum，参数和yum命令几乎一样，同时安装wget，后面需要单独下载一些 rpm包

1. [root@localhost yum.repos.d]# yum install -y dnf wget
2. ...
3. Installed:
4. dnf.noarch 0:4.0.9.2-1.el7_6
6. Dependency Installed:
7. deltarpm.x86_64 0:3.6-3.el7 dnf-data.noarch 0:4.0.9.2-1.el7_6
8. libcomps.x86_64 0:0.1.8-14.el7 libdnf.x86_64 0:0.22.5-1.el7_6
9. libmodulemd.x86_64 0:1.6.3-1.el7 librepo.x86_64 0:1.8.1-7.el7
10. libreport-filesystem.x86_64 0:2.1.11-53.el7.centos libsolv.x86_64 0:0.6.34-4.el7
11. python-enum34.noarch 0:1.0.4-1.el7 python2-dnf.noarch 0:4.0.9.2-1.el7_6
12. python2-hawkey.x86_64 0:0.22.5-1.el7_6 python2-libcomps.x86_64 0:0.1.8-14.el7
13. python2-libdnf.x86_64 0:0.22.5-1.el7_6
15. Complete!

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2、安装CentOS 8发行包

下载CentOS 8的发行包，之所以先下载不直接安装，是因为直接安装有太多依赖，我们需要用–nodeps手动安装，

1. [root@localhost home]# wget https://mirrors.aliyun.com/centos/8.2.2004/BaseOS/x86_64/os/Packages/centos-release-8.2-2.2004.0.1.el8.x86_64.rpm
2. [root@localhost home]# ls
3. centos centos-release-8.2-2.2004.0.1.el8.x86_64.rpm
4. [root@localhost home]# rpm -Uvh centos-release-8.2-2.2004.0.1.el8.x86_64.rpm --nodeps
5. warning: centos-release-8.2-2.2004.0.1.el8.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID 8483c65d: NOKEY
6. Preparing... ################################# [100%]
7. Updating / installing...
8. 1:centos-release-8.2-2.2004.0.1.el8################################# [ 50%]
9. Cleaning up / removing...
10. 2:centos-release-7-6.1810.2.el7.cen################################# [100%]

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3、添加CentOS 8 base repo

为了下载速度快一点，我们使用阿里云的yum源，

1. [root@localhost yum.repos.d]# wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo

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4、安装CentOS 8 EPEL release

1. [root@localhost yum.repos.d]# rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
2. Retrieving https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
3. warning: /var/tmp/rpm-tmp.tR2kHM: Header V3 RSA/SHA256 Signature, key ID 2f86d6a1: NOKEY
4. Preparing... ################################# [100%]
5. Updating / installing...
6. 1:epel-release-8-8.el8 ################################# [ 50%]
7. Cleaning up / removing...
8. 2:epel-release-7-12 ################################# [100%]

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5、删除冲突组件

有一些组件在8系列会有冲突，比如内核包，因此我们提前卸载，也可以等你升级时报错，看有哪些有冲突再卸载

1. rpm -e kernel sysvinit-tools gdbm kexec-tools systemd-sysv yum --nodeps

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6、开始升级

按照CentOS 8发行版的repo，更新当前系统上组件到对应的CentOS 8版本，耗时会久一点，

1. [root@localhost home]# dnf --allowerasing distro-sync -y

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7、安装内核

1. [root@localhost boot]# dnf -y install kernel
2. ...
3. Installed:
4. kernel-4.18.0-193.14.2.el8_2.x86_64 kernel-core-4.18.0-193.14.2.el8_2.x86_64
5. kernel-modules-4.18.0-193.14.2.el8_2.x86_64
7. Complete!

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8、重启系统

1. [root@localhost home]# reboot

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9、查看系统版本和内核

1. [root@localhost ~]# uname -a
2. Linux localhost 4.18.0-193.14.2.el8_2.x86_64 #1 SMP Sun Jul 26 03:54:29 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
3. [root@localhost ~]# cat /etc/redhat-release
4. CentOS Linux release 8.2.2004 (Core)

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