这篇文章以具体的示例来介绍一下从CentOS 7升级值CentOS 8的方法。
事前准备
最小化安装CentOS 7，具体版本如下所示：7.6.1810
代码语言：javascript复制[root@liumiao ~]# uname -a
Linux devops 3.10.0-957.el7.x86_64 #1 SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@liumiao ~]# cat /etc/redhat-release
CentOS Linux release 7.6.1810 (Core)
[root@liumiao ~]# 步骤1: 安装epel-relase、yum-utils和rpmconf
执行命令：yum install yum-utils epel-release -y
执行日志如下所示：
代码语言：javascript复制...省略
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Installing:
epel-release noarch 7-11 extras 15 k
yum-utils noarch 1.1.31-52.el7 base 121 k
Installing for dependencies:
libxml2-python x86_64 2.9.1-6.el7_2.3 base 247 k
python-chardet noarch 2.2.1-3.el7 base 227 k
python-kitchen noarch 1.1.1-5.el7 base 267 k
Transaction Summary
========================================================================================================================================
Install 2 Packages ( 3 Dependent packages)
...省略安装命令：yum install rpmconf -y
安装日志如下所示：
代码语言：javascript复制[root@liumiao ~]# yum install rpmconf -y
...省略
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Installing:
rpmconf noarch 0.3.4-1.el7 epel 21 k
Transaction Summary
========================================================================================================================================
Install 1 Package
...省略
Complete!
[root@liumiao ~]#步骤2: 安装前检查
检查配置：rpmconf -a
执行日志如下所示，如有选择直接使用缺省设定。
代码语言：javascript复制[root@liumiao ~]# rpmconf -a
[root@liumiao ~]# 检查叶节点：列出和其他RPM没有依赖的软件包
代码语言：javascript复制[root@liumiao ~]# package-cleanup --leaves
Loaded plugins: fastestmirror
libsysfs-2.1.0-16.el7.x86_64
[root@liumiao ~]# 检查不再提供的软件包：列出当前仓库中不提供升级的软件包信息
代码语言：javascript复制[root@liumiao ~]# package-cleanup --orphans
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.bit.edu.cn
* epel: hkg.mirror.rackspace.com
* extras: mirror.bit.edu.cn
* updates: ap.stykers.moe
GeoIP-1.5.0-13.el7.x86_64
...省略
yum-plugin-fastestmirror-1.1.31-50.el7.noarch
[root@liumiao ~]#步骤3: 安装dnf 并执行dnf update
CentOS 8使用dnf作为缺省的包管理工具，使用yum安装自己的替代工具dnf并删除自己。
安装命令：yum install dnf -y
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# yum install dnf -y
...省略
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Installing:
dnf noarch 4.0.9.2-1.el7_6 extras 357 k
Installing for dependencies:
deltarpm x86_64 3.6-3.el7 base 82 k
dnf-data noarch 4.0.9.2-1.el7_6 extras 51 k
libcomps x86_64 0.1.8-12.el7 extras 75 k
libdnf x86_64 0.22.5-1.el7_6 extras 533 k
libmodulemd x86_64 1.6.3-1.el7 extras 141 k
librepo x86_64 1.8.1-7.el7 base 81 k
libreport-filesystem x86_64 2.1.11-43.el7.centos base 40 k
libsolv x86_64 0.6.34-4.el7 base 329 k
libyaml x86_64 0.1.4-11.el7_0 base 55 k
python-enum34 noarch 1.0.4-1.el7 base 52 k
python2-dnf noarch 4.0.9.2-1.el7_6 extras 414 k
python2-hawkey x86_64 0.22.5-1.el7_6 extras 68 k
python2-libcomps x86_64 0.1.8-12.el7 extras 47 k
python2-libdnf x86_64 0.22.5-1.el7_6 extras 608 k
Transaction Summary
========================================================================================================================================
Install 1 Package ( 14 Dependent packages)
...省略
[root@liumiao ~]#清除yum：dnf -y remove yum yum-metadata-parser && rm -rf /etc/yum
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# dnf -y remove yum yum-metadata-parser
Dependencies resolved.
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Removing:
yum noarch 3.4.3-161.el7.centos @System 5.6 M
yum-metadata-parser x86_64 1.1.4-10.el7 @System 57 k
Removing dependent packages:
yum-plugin-fastestmirror noarch 1.1.31-50.el7 @System 53 k
yum-utils noarch 1.1.31-52.el7 @System 337 k
Transaction Summary
========================================================================================================================================
Remove 4 Packages
Freed space: 6.0 M
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Erasing : yum-utils-1.1.31-52.el7.noarch 1/4
Erasing : yum-plugin-fastestmirror-1.1.31-50.el7.noarch 2/4
Erasing : yum-3.4.3-161.el7.centos.noarch 3/4
Erasing : yum-metadata-parser-1.1.4-10.el7.x86_64 4/4
Verifying : yum-3.4.3-161.el7.centos.noarch 1/4
Verifying : yum-metadata-parser-1.1.4-10.el7.x86_64 2/4
Verifying : yum-plugin-fastestmirror-1.1.31-50.el7.noarch 3/4
Verifying : yum-utils-1.1.31-52.el7.noarch 4/4
Removed:
yum-3.4.3-161.el7.centos.noarch yum-metadata-parser-1.1.4-10.el7.x86_64 yum-plugin-fastestmirror-1.1.31-50.el7.noarch
yum-utils-1.1.31-52.el7.noarch
Complete!
[root@liumiao ~]# ls /etc/yum
pluginconf.d protected.d vars
[root@liumiao ~]# rm -rf /etc/yum
[root@liumiao ~]#就像使用yum update那样使用dnf update进行更新。
代码语言：javascript复制[root@liumiao ~]# dnf upgrade
Extra Packages for Enterprise Linux 7 - x86_64 5.6 MB/s | 16 MB 00:02
CentOS-7 - Base 3.5 MB/s | 10 MB 00:02
CentOS-7 - Updates 2.9 MB/s | 5.4 MB 00:01
CentOS-7 - Extras 40 kB/s | 251 kB 00:06
...省略
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Upgrading:
epel-release noarch 7-12 epel 15 k
...省略
tzdata noarch 2019c-1.el7 updates 493 k
Installing dependencies:
bind-export-libs x86_64 32:9.11.4-9.P2.el7 base 1.1 M
geoipupdate x86_64 2.5.0-1.el7 base 35 k
kernel x86_64 3.10.0-1062.4.3.el7 updates 50 M
Transaction Summary
========================================================================================================================================
Install 3 Packages
Upgrade 164 Packages
Total download size: 259 M
Is this ok [y/N]: y
Downloading Packages:
...省略
Installed:
bind-export-libs-32:9.11.4-9.P2.el7.x86_64 geoipupdate-2.5.0-1.el7.x86_64 kernel-3.10.0-1062.4.3.el7.x86_64
Complete!
[root@liumiao ~]#使用dnf更新CentOS 8的包
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# dnf -y upgrade http://mirror.bytemark.co.uk/centos/8/BaseOS/x86_64/os/Packages/centos-release-8.0-0.1905.0.9.el8.x86_64.rpm
Extra Packages for Enterprise Linux 7 - x86_64 4.3 MB/s | 16 MB 00:03
Last metadata expiration check: 0:00:01 ago on Wed 20 Nov 2019 07:58:07 AM EST.
centos-release-8.0-0.1905.0.9.el8.x86_64.rpm 13 kB/s | 26 kB 00:01
Dependencies resolved.
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Upgrading:
centos-release x86_64 8.0-0.1905.0.9.el8 @commandline 26 k
Transaction Summary
========================================================================================================================================
Upgrade 1 Package
Total size: 26 k
Downloading Packages:
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Upgrading : centos-release-8.0-0.1905.0.9.el8.x86_64 1/2
Cleanup : centos-release-7-7.1908.0.el7.centos.x86_64 2/2
Verifying : centos-release-8.0-0.1905.0.9.el8.x86_64 1/2
Verifying : centos-release-7-7.1908.0.el7.centos.x86_64 2/2
Upgraded:
centos-release-8.0-0.1905.0.9.el8.x86_64
Complete!
[root@liumiao ~]#更新epel仓库
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# dnf -y upgrade https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
Extra Packages for Enterprise Linux 7 - x86_64 578 kB/s | 16 MB 00:28
CentOS-8 - Base 635 kB/s | 7.9 MB 00:12
CentOS-8 - Extras 1.7 kB/s | 2.1 kB 00:01
CentOS-8 - AppStream 1.3 MB/s | 6.3 MB 00:04
epel-release-latest-8.noarch.rpm 7.7 kB/s | 21 kB 00:02
Dependencies resolved.
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Upgrading:
epel-release noarch 8-7.el8 @commandline 21 k
Transaction Summary
========================================================================================================================================
Upgrade 1 Package
Total size: 21 k
Downloading Packages:
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Preparing : 1/1
Upgrading : epel-release-8-7.el8.noarch 1/2
Cleanup : epel-release-7-12.noarch 2/2
Verifying : epel-release-8-7.el8.noarch 1/2
Verifying : epel-release-7-12.noarch 2/2
Upgraded:
epel-release-8-7.el8.noarch
Complete!
[root@liumiao ~]# 此时确认版本信息，已经发生了变化
代码语言：javascript复制[root@liumiao ~]# cat /etc/redhat-release
CentOS Linux release 8.0.1905 (Core)
[root@liumiao ~]# 步骤4: 删除无用文件和CentOS 7的内核并安装CentOS 8的内核
删除无用的临时文件：dnf clean all
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# dnf clean all
62 files removed
[root@liumiao ~]#删除CentOS 7的旧核: rpm -e `rpm -q kernel`
执行日志如下所示：
代码语言：javascript复制[root@liumiao ~]# rpm -e `rpm -q kernel`
[root@liumiao ~]#确认删除冲突的包
代码语言：javascript复制[root@liumiao ~]# rpm -e --nodeps sysvinit-tools
[root@liumiao ~]# 更新CentOS 8系统
代码语言：javascript复制[root@liumiao ~]# dnf -y --releasever=8 --allowerasing --setopt=deltarpm=false distro-sync
Extra Packages for Enterprise Linux 8 - x86_64 2.0 MB/s | 3.5 MB 00:01
CentOS-8 - Base 160 kB/s | 7.9 MB 00:50
CentOS-8 - AppStream 1.6 MB/s | 6.3 MB 00:03
CentOS-8 - Extras 950 B/s | 2.1 kB 00:02
Last metadata expiration check: 0:00:02 ago on Wed 20 Nov 2019 08:09:51 AM EST.
Dependencies resolved.
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Upgrading:
rpmconf noarch 1.0.20-1.el8 epel 26 k
...省略
Removed:
deltarpm-3.6-3.el7.x86_64 libselinux-python-2.5-14.1.el7.x86_64 libxml2-python-2.9.1-6.el7_2.3.x86_64
newt-python-0.52.15-4.el7.x86_64 python-2.7.5-86.el7.x86_64 python-chardet-2.2.1-3.el7.noarch
python-firewall-0.6.3-2.el7_7.2.noarch python-kitchen-1.1.1-5.el7.noarch python-libs-2.7.5-86.el7.x86_64
python-linux-procfs-0.4.11-4.el7.noarch python-schedutils-0.4-6.el7.x86_64 python-slip-0.4.0-4.el7.noarch
python-slip-dbus-0.4.0-4.el7.noarch python-urlgrabber-3.10-9.el7.noarch python2-dnf-4.0.9.2-1.el7_6.noarch
python2-hawkey-0.22.5-1.el7_6.x86_64 python2-libcomps-0.1.8-12.el7.x86_64 python2-libdnf-0.22.5-1.el7_6.x86_64
pyxattr-0.5.1-5.el7.x86_64 rpm-python-4.11.3-40.el7.x86_64 systemd-sysv-219-67.el7_7.2.x86_64
Complete!
[root@liumiao ~]# 此时通过uname -a确认内核状态，仍是3.10.
代码语言：javascript复制[root@liumiao ~]# uname -a
Linux devops 3.10.0-957.el7.x86_64 #1 SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@liumiao ~]# cat /etc/redhat-release
CentOS Linux release 8.0.1905 (Core)
[root@liumiao ~]#由于前文已经更新，此时如执行dnf -y install kernel-core会提示already updated，接下来更新一下CentOS 8的最小化安装的相关package，执行如下命令即可：
代码语言：javascript复制[root@liumiao ~]# dnf -y groupupdate "Core" "Minimal Install"
Last metadata expiration check: 0:13:34 ago on Wed 20 Nov 2019 08:09:51 AM EST.
Dependencies resolved.
========================================================================================================================================
Package Arch Version Repository Size
========================================================================================================================================
Installing group/module packages:
dnf-plugin-spacewalk noarch 2.8.5-11.module_el8.0.0 180 337688dc AppStream 24 k
dnf-plugins-core noarch 4.0.2.2-3.el8 BaseOS 59 k
...省略
[root@liumiao ~]#步骤5: 重启系统
重启之后即可确认内核和版本文件信息均已升至最新
代码语言：javascript复制[root@liumiao ~]# uname -a
Linux devops 4.18.0-80.11.2.el8_0.x86_64 #1 SMP Tue Sep 24 11:32:19 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
[root@liumiao ~]# cat /etc/redhat-release
CentOS Linux release 8.0.1905 (Core)
[root@liumiao ~]# 以上就是本文的全部内容，希望对大家的学习有所帮助。
