一、背景
某业务系统因建设较早，使用的OS比较过时，还是centos6.5的系统，因国产化需要，需将该系统升级到BClinux 8.6，但官方显示不支持centos 6.x升级到8，需先将centos6.5升级到centos7的最新版，即centos7.9后再升级。后结合相关实践，Centos6.5只支持升级到最高Centos7.2版本（1511版本），之后再升级到7.9；因升级跨大版本升级，且Redhat官网 6.5YUM源已过期不可用，综上，特整理记录该升级过程，以作后期参考指导，不妥之处，感谢批评指正。注意：升级到 RHEL 8 分为两个阶段。首先需要将系统从 RHEL 6 升级到 RHEL 7，然后再升级到 RHEL 8。升级前对重要数据备份，或对虚拟机做好快照，甚至整机备份。
RHEL 6 原位升级到 RHEL 8 需要以下主要步骤：
❥ 资源链接：从 RHEL 6 升级至 RHEL 8、wiki、Release Notes、kernel镜像站、RHEL 6 系统升级前准备
二、6.5升级7.2前准备
1）升级前版本确认：cat /etc/redhat-release
注意：7.2是支持升级的最高版本，升级其余版本将会出现Downloading failed: invalid data in .treeinfo: No section:'checksums’的错误提示；
解决单独分区挂载的/usr目录问题
mkdir /mnt/usr/
mkdir /mnt/root
mount --bind / /mnt/root
mount --bind /usr /mnt/usr
rsync -aHAXv /mnt/usr/* /mnt/root/usr/
删除/etc/fstab相关开机自动挂载配置项后，reboot重启
2）更换YUM源：
由于 CentOS 6 已停产，我们需要将 yum 指向 vault 仓库，执行以下命令：
#备份原有的
cd /etc/yum.repos.d/
mkdir repo6_backup
mv *.repo ./repo6_backup
#下载vault 仓库的repo
curl https://www.getpagespeed.com/files/centos6-eol.repo --output /etc/yum.repos.d/CentOS-Base.repo
或
wget https://www.getpagespeed.com/files/centos6-eol.repo -O /etc/yum.repos.d/CentOS-Base.repo
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
#因官方源不可用，故需修改配置更新源到其他镜像站
vi /etc/yum.repos.d/upgrade.repo //如下所示
[upgrade]
name=upgrade
baseurl=https://buildlogs.centos.org/centos/6/upg/x86_64/
enable=1
gpgcheck=0
#安装升级助手
yum erase openscap -y #由于centos 6.5自带的安全助手版本较高，卸载了装个更老的，更多参见http://www.open-scap.org/，Security Content Automation Protocol（SCAP）
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm
yum install redhat-upgrade-tool preupgrade-assistant-contents -y #或者尝试以下链接
yum install ftp://ftp.pbone.net/mirror/ftp.scientificlinux.org/linux/scientific/6.5/x86_64/updates/fastbugs/openscap-1.0.8-1.el6_5.x86_64.rpm -y
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm -y
#如果提示：No package redhat-upgrade-tool available，执行
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/preupgrade-assistant-1.0.2-33.0.3.el6.centos.x86_64.rpm -y
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/preupgrade-assistant-contents-0.5.13-1.0.5.el6.centos.noarch.rpm -y
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/preupgrade-assistant-ui-1.0.2-33.0.3.el6.centos.x86_64.rpm -y
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/redhat-upgrade-tool-0.7.22-3.el6.centos.noarch.rpm -y
3）升级助力检测升级环境确认正常后update
#升级前检测，该过程会看到哪些包将受到此升级的影响
preupg -l //该命令会耗费几分钟到几十分钟时间
preupg -s CentOS6_7 //运行模拟升级工具，不过真的升级，相当于升级检测，升级检测通过后，在线下载centos7镜像,或本地上传后使用本地镜像也可以
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 #此处输入y
Gathering logs used by preupgrade assistant:
All installed packages : 01/11 …finished (time 00:00s)
All changed files : 02/11 …finished (time 02:44s)
Changed config files : 03/11 …finished (time 00:00s)
All users : 04/11 …finished (time 00:00s)
All groups : 05/11 …finished (time 00:00s)
Service statuses : 06/11 …finished (time 00:00s)
All installed files : 07/11 …finished (time 00:02s)
…
Tarball with results is stored here /root/preupgrade-results/preupg_results-210324171443.tar.gz .
The latest assessment is stored in directory /root/preupgrade .
Summary information:
We found some critical issues. In-place upgrade is not advised.
Read the file /root/preupgrade/result.html for more details.
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 .
#根据模拟升级的检测结果进行确认和评估，存在EXTREME错误则无法进行下一步升级操作
preupg --riskcheck --verbose
#导入RPM签名证书，下面任选其一
rpm --import https://mirrors.ustc.edu.cn/epel/RPM-GPG-KEY-EPEL-7
rpm --import http://mirror.centos.org/centos/7/os/x86_64/RPM-GPG-KEY-CentOS-7
rpm --import http://vault.centos.org/centos/7.0.1406/os/x86_64/RPM-GPG-KEY-CentOS-7
#在线update，一般不满足条件，任选其一执行，建议使用清华大学的源：
centos-upgrade-tool-cli --network 7 --instrepo=http://mirror.centos.org/centos/7/os/x86_64
centos-upgrade-tool-cli --network 7 --instrepo=https://mirrors.ustc.edu.cn/centos/7/os/x86_64 #或
centos-upgrade-tool-cli --network 7 --force --instrepo=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/7.2.1511/os/x86_64/
centos-upgrade-tool-cli --network 7 --instrepo=http://vault.centos.org/centos/7.0.1406/os/x86_64/
…
Continue with the upgrade [Y/N]? y
…
rpm install 100% [============================================================================================]
setting up system for upgrade
Finished. Reboot to start upgrade.
#离线update
wget --no-check-certificate https://archive.kernel.org/centos-vault/7.2.1511/isos/x86_64/CentOS-7-x86_64-Everything-1511.iso #可以用CentOS-7-x86_64-DVD-1511.iso ，只有4G
wget --no-check-certificate https://vault.centos.org/7.2.1511/isos/x86_64/CentOS-7-x86_64-Everything-1511.iso(7.2G)
md5sum //CentOS-7-x86_64-Everything-1511.iso
dba29c59117400b111633be2bf2aaf0e CentOS-7-x86_64-Everything-1511.iso
mout -o -loop -t iso9660 /home/CentOS-7-x86_64-Everything-1511.iso /mnt/cdrom
centos-upgrade-tool-cli --iso=/home/CentOS-7-x86_64-Everything-1511.iso #或
centos-upgrade-tool-cli --device=/dev/cdrom //输出类似如下：
……
setting up repos...
.treeinfo | 1.1 kB 00:00
getting boot p_w_picpaths...
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.
#或者直接执行：
cd /etc/yum.repos.d
wget http://mirrors.aliyun.com/repo/Centos-7.repo
wget https://mirrors.aliyun.com/repo/epel-7.repo
或
mount -t iso9660 -o loop CentOS-7-x86_64-DVD-1511.iso /mnt/iso #或者
mount -t auto /dev/cdrom /mnt/iso/
vi /etc/yum.repos.d/centos7.repo //如下
[centos7]
name=CentOS 7
baseurl=file:///mnt/iso
enabled=1
gpgcheck=0
yum clean all
yum makecache
yum update #升级所有包同时也升级软件和系统内核
#更新lib库
ln -s /usr/lib64/libsasl2.so.3.0.0 /usr/lib64/libsasl2.so.2
ln -s /usr/lib64/libpcre.so.1.2.0 /usr/lib64/libpcre.so.0
#升级完成后重启。重启后，将使用 redhat-upgrade-tool 内核启动完成CentOS 6升级
reboot //若是提示The requested URL returned error: 404 Not Found等错误，基本上说明当前系统不支持直接升级,恢复后重装替换吧
#验证
cat /etc/centos-release
#更新软件版本
yum upgrade
rpm -qa | grep el6 #查看系统上残留的软件包，尽量清理掉
注：当preupg命令在没有其他选项的情况下运行时，它会在目录中生成result.html和preupg_results-*.tar.gz文件/root/preupgrade/；评估结果保存在/root/preupgrade-results/preupg_results-190130083547.tar.gz，进行系统升级前评估，用图形界面打开查看评估报告，解决对应问题。另，/var/log/upgrade.log文件列出了升级阶段发现的问题。利用yum check dependencies命令检查依赖错误；
4）重启后配置调整共享库：相关经验表明升级后会出现共享库导致ssh，命令执行登异常问题
三、7.2升级到7.9过程
#yum配置参考上文，这里如果想先升级到6.10，配置本地6.10的YUM
wget https://vault.centos.org/6.10/isos/x86_64/CentOS-6.10-x86_64-LiveDVD.iso
mount /dev/sr0 /mnt/
cat /etc/yum.repos.d/dev.repo
[dev]
name=dev
baseurl=file:///mnt
gpgcheck=0
enabled=1
yum clean all
yum makecache
yum update -y #就地从centos6.5升级到6。10
#下载7.9安装包
wget https://mirrors.ustc.edu.cn/centos/7.9.2009/isos/x86_64/CentOS-7-x86_64-DVD-2009.iso
#本地挂载
mount /dev/sr0 /centos10/
#配置7.10本地yum源
cat /etc/yum.repos.d/centos10.repo
[centos10]
name=centos10
baseurl=file:///centos10/
gpgcheck=0
#6.9升级到7.10,参考上文先评估
yum install preupgrade-assistant preupgrade-assistant-ui preupgrade-assistant-el6toel7 redhat-upgrade-tool
preupg -l //无报错后再执行升级
redhat-upgrade-tool --device /mnt/
四、过程报错处理
4.1、安装redhat-upgrade-tool时报错File contains no section headers
这是因为repo配置文件错误，缺少YUM repo头信息；解决方案：将缺少的yum头信息添加上 [centos6-upgrade]，如下所示：
[centos6-upgrade]
name=CentOS-$releasever - Upgrade Tool
baseurl=http://dev.centos.org/centos/6/upg/x86_64/
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
4.2、安装redhat-upgrade-tool时报错Couldn’t resolve host dev.centos.org
centos官网已经停止centos6相关服务，网站dev.centos.org已经停止服务。这里我们用离线方式手动安装redhat-upgrade-tool相关的rpm包。或换成https://buildlogs.centos.org/centos/6/upg/x86_64/
4.3、模拟升级时报错：无法导入openscap相关文件
上图报错是因为openscap版本太高，需要降级；解决方案：卸载当前安装的openscap版本，下载并安装openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm，执行：
rpm -qa |grep openscap //验证当前版本
openscap-1.2.13-2.el6.x86_64
rpm -e --nodeps openscap-1.2.13-2.el6.x86_64
wget https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm
yum localinstall openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm -y #或执行
yum install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm
4.4、模拟升级的检测结果报错：X11的EXTREME问题
preupg --riskcheck --verbose //报错如下
……
INPLACERISK: EXTREME:You have GMOME Desktop Environment session as an option in your X11 session manager. CHOME Desktop Environment as a part of the yum group’Desktop’undervent serious redesign in its user interface as well as underlying technologies in Centos 7.
TCLACERISK: EXTREME: You have kDE Desktop Envirom ent session as an option in your X11session manager. KDE Desktop Environment as a part of the yum group’KDE Desktop’undervent a redesign in its user interface as well as underlying technologies in Centos 7.
TMPLACERISK: FXTREE:The kernel driver’ncnet32’reauired to service hardware present in vour svsten is not available in Centos 7. This suggests that your systen contains hardware that is not supported in CentOS 7 release.
这是由于centos7对X11桌面环境进行了重新设计；而centos6当前安装软件没有桌面要求，选择卸载X11桌面环境。执行：yum groupremove -y “Desktop” “X Window System”
4.5、模拟升级的检测结果存在：关于pcnet32的EXTREME问题
报错信息：
这是因某些资源采用vmware，它提供的默认网卡类型是pcnet32，el7默认没有提供pcnet32的网卡驱动。
解决方案：在vmware指定的虚拟机存储位置找到.vmx的文件，ethernet0.virtualDev = “pcnet32” 或是别的。将其修改为：
ethernet0.virtualDev = “e1000”’ （如果没有收到添加）
4.6、升级后提示库文件加载失败，报错：grep: error while loading shared libraries: libpcre.so.0: cannot open shared object file: No such file or director
ls -l /usr/lib64/libpcre.so* //查看升级后centos7的相关库
lrwxrwxrwx 1 root root 16 3月 15 14:13 /usr/lib64/libpcre.so -> libpcre.so.1.2.0
lrwxrwxrwx 1 root root 16 3月 15 14:12 /usr/lib64/libpcre.so.1 -> libpcre.so.1.2.0
-rwxr-xr-x 1 root root 398272 11月 20 2015 /usr/lib64/libpcre.so.1.2.0
#相关实践表明，centos7中只需对libpcre.so.0做软连接指向就行，执行
ln -s /usr/lib64/libpcre.so.1.2.0 /usr/lib64/libpcre.so.0
ln -s /lib64/libpcre.so.1 /lib64/libpcre.so.0
ln -s /usr/lib64/libsasl2.so.3.0.0 /usr/lib64/libsasl2.so.2
4.7、yum update出现python问题
#挂载7的镜像
mount -t iso9660 -o loop CentOS-7-x86_64-DVD-1511.iso /mnt/iso或者
mount -t auto /dev/cdrom /mnt/iso/
#备份
mv yum.repos.d yum.repos.d_backup
mkdir yum.repos.d
#7 YUM源
vi /etc/yum.repos.d/centos7.repo //如下
[centos7]
name=CentOS 7
baseurl=file:///mnt/iso
enabled=1
gpgcheck=0
#重装python2
yum reinstall python -y
相关资源：yum FAQ
4.8、升级后无法进行ssh登录（缺失文件libsasl2.so.2）
1）本地控制台登录后，执行：journalctl -f -u sshd，可以看到报错缺失文件libsasl2.so.2，如下所示：
2）yum也不能使用也是因为确实libsasl2.so.2文件，这里我们也做下软连接：
##Centos 7中是有libsasl2.so.2这个库的，只不过换了名字，进入到/usr/lib64/目录下查看
cd /usr/lib64
ls libsasl2.so.* -l //如下所示
lrwxrwxrwx. 1 root root 17 Oct 17 2016 libsasl2.so.3 -> libsasl2.so.3.0.0
-rwxr-xr-x. 1 root root 121296 Jun 10 2014 libsasl2.so.3.0.0
#做软连接到libsasl2.so.2
ln -s libsasl2.so.3 libsasl2.so.2
ls libsasl2.so.* -l //如下所示
lrwxrwxrwx 1 root root 13 Nov 19 18:00 libsasl2.so.2 -> libsasl2.so.3
lrwxrwxrwx. 1 root root 17 Oct 17 2016 libsasl2.so.3 -> libsasl2.so.3.0.0
-rwxr-xr-x. 1 root root 121296 Jun 10 2014 libsasl2.so.3.0.0
#重启ssh
systemctl start sshd
#更新yum源
wget http://mirrors.aliyun.com/repo/Centos-7.repo
wget https://mirrors.aliyun.com/repo/epel-7.repo
yum clean all
yum makecache
4.9、grep命令报错，缺失libpcre.so.0文件
grep //报错如下
grep: error while loading shared libraries: libpcre.so.0: cannot open shared object file: No such file or directory
#方法同4.6，加软连接
cd /usr/lib64
ls libpcre.so* //显示如下
libpcre.so libpcre.so.1 libpcre.so.1.2.0
ln -s libpcre.so.1 libpcre.so.0
4.10、网卡启动失败，但是ip地址获取正常，报错：Failed to start LSB: Bring up/down networking.
造成网卡不能使用的原因是，系统后MAC地址已经更改但是在系统内部的配置文件还没有更，这就导致了真实的MAC地址与配置文件中的MAC地址不一致。Failed to start LSB: Bring up/down networking 的报错就是因为升级后真实的MAC地址与配置文件的MAC地址不相符造成的，可采用如下3种办法调试恢复，最后不要忘了重启系统。
第一种办法直接关闭NetworManager，执行：systemctl stop NetworkManager ，centos7系统没启动这个服务
第二种办法修改配置文件
第三种办法：使用这一条命令将清除协议地址，尽然还是不管用，无奈之下重启系统，发现重启后网络服务恢复正常。
ip addr flush dev ens33/eth0 这个方法是可以成功解决问题的
4.11、YUM清理卸载openldap导致libldap-2.4.so.2: cannot open shared object file
注意：当卸载掉openldap后，出现了yum、sshd奔溃的问题；
wget http://ftp.pbone.net/mirror/ftp.scientificlinux.org/linux/scientific/6.4/x86_64/updates/fastbugs/openldap-2.4.23-32.el6_4.1.x86_64.rpm
rpm -ivh --force --nodeps openldap-2.4.23-32.el6_4.1.x86_64.rpm
五、Centos 7.9升级到BCLinux 8.6
六、附录：其他
6.1、CentOS 8中执行命令报错：Failed to set locale, defaulting to C.UTF-8
原因：
解决方法1：
解决方法2：
6.2、内核版本的定义：
版本性质：主分支ml(mainline)，稳定版(stable)，长期维护版lt(longterm)
版本命名格式为 “A.B.C”：
#内核升级
#yum源
wget http://www.elrepo.org/elrepo-release-6-6.el6.elrepo.noarch.rpm #Centos 6 YUM源：
wget http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm #Centos 7 YUM源：
rpm -import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
#查看可用的内核
yum --disablerepo="*" --enablerepo="elrepo-kernel" list available
#安装最新主线稳定版
yum -y --enablerepo=elrepo-kernel install kernel-ml
#方式2：直接rpm安装
wget https://elrepo.org/linux/kernel/el7/x86_64/RPMS/kernel-lt-4.4.185-1.el7.elrepo.x86_64.rpm
rpm -ivh kernel-lt-4.4.185-1.el7.elrepo.x86_64.rpm
#方式3：编译安装
#升级完成，修改grub内核启动顺序，内核升级完毕后，目前内核还是默认的版本，如果此时直接执行reboot命令，重启后使用的内核版本还是默认的3.10，不会使用新的5.2.2
cat /boot/grub2/grub.cfg | grep menuentry //查看当前内核数
awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg //查看默认启动顺序
#在grub.conf文件中决定开机使用哪个内核版本做启动的参数是default，默认值为0，代表从最新的内核启动。代表启动的内核版本从上往下依次是0、1、2等，修改新内核的启动顺序为0：
vim /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=0 #参数default更改为0即可
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
#重新生成内核配置
grub2-mkconfig -o /boot/grub2/grub.cfg
#或者
grub2-set-default ‘CentOS Linux (3.10.0-123.9.3.el7.x86_64) 7 (Core)’
#验证
grub2-editenv list
#CentOS 8 系统更改内核启动顺序与centos 7有了一些变化
grubby --default-kernel //查看默认启动内核
grubby --info=ALL //查看所有内核
rubby --set-default /boot/vmlinuz-4.18.0-80.11.2.el8_0.x86_64 //cenots8设置需要设置的启动的默认的内核
#对于ubuntu
vim /etc/default/grub #将GRUB_DEFAULT=0 修改为
GRUB_DEFAULT=“Advanced options for Ubuntu>Ubuntu, with Linux 3.13.0-166-generic”
#更新修改后的grub
update-grub
#完成后，重启
reboot
