centos7升级centos8（亲测好用）
#Centos 7 => 8 manual upgrade.
#No support is given, YMMV, remember backups!
#Tested with upcloud and cloudatcost.
Get ready to upgrade
yum -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
yum -y install rpmconf yum-utils
Resolve all config stuff.
rpmconf -a
Packages you might not need/require, remove if something doens’t seem to be required.
package-cleanup --leaves
package-cleanup --orphans
Install DNF.
yum -y install dnf
Remove yum
dnf -y remove yum yum-metadata-parser
rm -Rf /etc/yum
Upgrade system to be up-to-date
dnf -y upgrade
Install new versions:
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
Upgrade EPEL
dnf -y upgrade https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
Dnf clean
dnf clean all
Remove kernels, kernel packages are kernel-core in c8.
rpm -e 'rpm -q kernel'
Remove definitely conflicting stuff.
rpm -e --nodeps sysvinit-tools
Try to run the upgrade
dnf -y --releasever=8 --allowerasing --setopt=deltarpm=false distro-sync
If it doesn’t succeed (YMMV), fix dependency stuff by removing/installing conficting stuff and try again.
eg. if you want to drop all the dependencies
#dnf remove python2-six python-six
#eg. you don’t want to drop all the dependencies, they would remove too much.
#rpm -e --nodeps sysvinit-tools
Process new configs
rpmconf -a
Ensure kernel is properly installed
rpm -e kernel-core
dnf -y install kernel-core
Make sure grub is updated (ensure that it’s right place!)
ROOTDEV='ls /dev/*da|head -1';
echo “Detected root as $ROOTDEV…”
grub2-install $ROOTDEV
Install new stuff that is in the Core/Minimum Install:
dnf -y groupupdate “Core” “Minimal Install”
Install back the stuff that you need and removed to get the dnf distro-sync to succeed.
来源：https://blog.csdn.net/Pangshibo233/article/details/102740475