1、将系统所有包升级到最新：

apt update
apt dist-upgrade

2、停止所有的VM/CT，执行pve5to6命令检查升级潜在的问题-------实测中，未关闭虚拟机也正常。生产环境建议关闭并备份

pve5to6

3、检查通过后，升级到Corosync3版本

systemctl stop pve-ha-lrm
systemctl stop pve-ha-crm

添加Corosync3的源：

Ⅰ、国外源

echo "deb http://download.proxmox.com/debian/corosync-3/ stretch main" > /etc/apt/sources.list.d/corosync3.list

Ⅱ、国内源

echo "deb http://mirrors.ustc.edu.cn/proxmox/debian/corosync-3/ stretch main"> /etc/apt/sources.list.d/corosync3.list

升级Corosync3，期间不可对任何VM/CT或群集进行更改

Ⅰ、非集群

apt update && apt dist-upgrade -y

Ⅱ、集群

如果是集群，则需要在每个节点上先下载：

apt dist-upgrade --download-only

然后在所有节点上执行升级：

apt dist-upgrade**

所有节点更新完成后，重启服务

systemctl start pve-ha-lrm && systemctl start pve-ha-crm

4、升级到Proxmox VE6.0

修改源为6.0版本

Ⅰ、国外源

sed -i 's/stretch/buster/g' /etc/apt/sources.list
sed -i -e 's/stretch/buster/g' /etc/apt/sources.list.d/pve-install-repo.list
echo "deb http://download.proxmox.com/debian/ceph-luminous buster main" > /etc/apt/sources.list.d/ceph.list

Ⅱ、国内源

echo "deb http://mirrors.ustc.edu.cn/proxmox/debian/ buster pve-no-subscription" > /etc/apt/sources.list.d/pve-install-repo.list
echo "deb http://mirrors.ustc.edu.cn/proxmox/debian/ceph-luminous buster main" > /etc/apt/sources.list.d/ceph.list

（直接更改，如已改为国内源亦可执行这步）

sed -i 's/stretch/buster/g' /etc/apt/sources.list

如未修改过，则

nano /etc/apt/sources.list

替换以下源

deb http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb http://mirrors.aliyun.com/debian-security buster/updates main
deb-src http://mirrors.aliyun.com/debian-security buster/updates main
deb http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
deb https://mirrors4.tuna.tsinghua.edu.cn/proxmox/debian buster pve-no-subscription

升级系统

apt update && apt dist-upgrade -y

在升级过程中有一些配置选择，请根据提示操作。特别注意有安装Grub的选项，请用空格键选择要安装Grub的分区

删除额外的corosync3软件源

rm -rf /etc/apt/sources.list.d/corosync3.list

升级过程中遇到错误如下：

dpkg: error processing package initramfs-tools (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
initramfs-tools

解决方法在https://ubuntuforums.org/showthread.php?t=1990236找到了：

rm -f /var/lib/dpkg/info/initramfs-tools.post*
rm -f /var/lib/dpkg/info/initramfs-tools.pre*
rm -f /var/lib/dpkg/info/bcmwl-kernel-source.post*
rm -f /var/lib/dpkg/info/bcmwl-kernel-source.pre*
dpkg --configure -a