升级过程主要参考
https://blog.csdn.net/lic95/article/details/124991999
执行 leapp preupgrade 后，/var/log/leapp/leapp-report.txt 主要报错包括
Risk Factor: high (inhibitor)
Title: Missing required answers in the answer file
Summary: One or more sections in answerfile are missing user choices: remove_pam_pkcs11_module_check.confirm
For more information consult https://leapp.readthedocs.io/en/latest/dialogs.html
Remediation: [hint] Please register user choices with leapp answer cli command or by manually editing the answerfile.
[command] leapp answer --section remove_pam_pkcs11_module_check.confirm=True
Key: d35f6c6b1b1fa6924ef442e3670d90fa92f0d54b
必须执行 leapp answer --section remove_pam_pkcs11_module_check.confirm=True，升级才可以完成
Risk Factor: high
Title: Transition from Docker to Podman in RHEL8
Summary: Docker has been deprecated in favour of Podman in Red Hat Enterprise Linux 8. The docker package is going to be removed during the upgrade without migration of existing containers.
Remediation: [hint] It is recommended to re-create the containers with the appropriate container images and reattach any in-use volumes using podman directly prior to the upgrade of the operating system, which should provide the same level of functionality.
Key: b68cb32bb7c0f466ba48f97981c3ba7c27faf148
RHEL8中没有docker了，这也是本次升级遇到的最大麻烦
Risk Factor: high
Title: Difference in Python versions and support in RHEL 8
Summary: In RHEL 8, there is no 'python' command. Python 3 (backward incompatible) is the primary Python version and Python 2 is available with limited support and limited set of packages. Read more here: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/configuring_basic_system_settings/#using-python3
Remediation: [hint] Please run "alternatives --set python /usr/bin/python3" after upgrade
Key: 0c98585b1d8d252eb540bf61560094f3495351f5
只要执行了leapp answer，就可以执行leapp upgrade。系统升级花费了一些时间，但是升级过程还比较顺利。不过升级完成后，docker没有了。
安装docker参考
https://www.cnblogs.com/Tiork/p/15736390.html
https://phoenixnap.com/kb/how-to-install-docker-on-centos-8
yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
在执行 yum install docker-ce --nobest 时失败了，依赖关系解决不了。于是乎执行
dnf install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.10-3.2.el7.x86_64.rpm
强行把containerd.io安装了。然后执行yum install docker-ce --nobest 就可以装进去了。虽然docker装进去了，但是已有的容器起不来了，
docker start 1567ad817138
Error response from daemon: Unknown runtime specified docker-runc
Error: failed to start containers: 1567ad817138
需要执行一下以下两句
grep -rl 'docker-runc' /var/lib/docker/containers/ | xargs sed -i 's/docker-runc/runc/g'
systemctl restart docker
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