Anhand dieser Doku sollte ein Update von PVE Version 7.x zu 8.x durchführbar sein.
Doku von Proxmox selbst: https://pve.proxmox.com/wiki/Upgrade_from_7_to_8

mkdir -p /root/backup/`date '+%Y%m%d'`
tar -czf /root/backup/`date '+%Y%m%d'`/pve-cluster-backup.tar.gz /var/lib/pve-cluster
tar -czf /root/backup/`date '+%Y%m%d'`/ssh-backup.tar.gz /root/.ssh
tar -czf /root/backup/`date '+%Y%m%d'`/corosync-backup.tar.gz /etc/corosync
cp /etc/hosts /root/backup/`date '+%Y%m%d'`/
cp /etc/network/interfaces /root/backup/`date '+%Y%m%d'`/

apt-get update
apt-get dist-upgrade
reboot

PVE bringt wieder Upgrade Check mit. Mit diesem kann man checken lassen ob ein Upgrade möglich wäre.

Beispiel:
root@pve01:~$ pve7to8 --full
= CHECKING VERSION INFORMATION FOR PVE PACKAGES =

Checking for package updates..
PASS: all packages up-to-date

Checking proxmox-ve package version..
PASS: proxmox-ve package has version >= 7.4-1

Checking running kernel version..
PASS: running kernel '5.15.108-1-pve' is considered suitable for upgrade.

= CHECKING CLUSTER HEALTH/SETTINGS =

PASS: systemd unit 'pve-cluster.service' is in state 'active'
PASS: systemd unit 'corosync.service' is in state 'active'
PASS: Cluster Filesystem is quorate.

Analzying quorum settings and state..
INFO: configured votes - nodes: 3
INFO: configured votes - qdevice: 0
INFO: current expected votes: 3
INFO: current total votes: 3

Checking nodelist entries..
PASS: nodelist settings OK

Checking totem settings..
PASS: totem settings OK

INFO: run 'pvecm status' to get detailed cluster status..

= CHECKING HYPER-CONVERGED CEPH STATUS =

SKIP: no hyper-converged ceph setup detected!

= CHECKING CONFIGURED STORAGES =

file /etc/pve/storage.cfg line 10 (section 'TrueNAS') - unable to parse value of 'prune-backups': invalid format - value without key, but schema does not define a default key

PASS: storage 'TrueNAS' enabled and active.
PASS: storage 'local' enabled and active.
INFO: Checking storage content type configuration..
PASS: no storage content problems found
PASS: no storage re-uses a directory for multiple content types.

= MISCELLANEOUS CHECKS =

INFO: Checking common daemon services..
PASS: systemd unit 'pveproxy.service' is in state 'active'
PASS: systemd unit 'pvedaemon.service' is in state 'active'
PASS: systemd unit 'pvescheduler.service' is in state 'active'
PASS: systemd unit 'pvestatd.service' is in state 'active'
INFO: Checking for supported & active NTP service..
PASS: Detected active time synchronisation unit 'chrony.service'
INFO: Checking for running guests..
PASS: no running guest detected.
INFO: Checking if the local node's hostname 'pve01' is resolvable..
INFO: Checking if resolved IP is configured on local node..
PASS: Resolved node IP '192.168.88.141' configured and active on single interface.
INFO: Check node certificate's RSA key size
PASS: Certificate 'pve-root-ca.pem' passed Debian Busters (and newer) security level for TLS connections (4096 >= 2048)
PASS: Certificate 'pve-ssl.pem' passed Debian Busters (and newer) security level for TLS connections (2048 >= 2048)
INFO: Checking backup retention settings..
PASS: no backup retention problems found.
INFO: checking CIFS credential location..
PASS: no CIFS credentials at outdated location found.
INFO: Checking permission system changes..
INFO: Checking custom role IDs for clashes with new 'PVE' namespace..
PASS: no custom roles defined, so no clash with 'PVE' role ID namespace enforced in Proxmox VE 8
INFO: Checking if LXCFS is running with FUSE3 library, if already upgraded..
SKIP: not yet upgraded, no need to check the FUSE library version LXCFS uses
INFO: Checking node and guest description/note length..
PASS: All node config descriptions fit in the new limit of 64 KiB
PASS: All guest config descriptions fit in the new limit of 8 KiB
INFO: Checking container configs for deprecated lxc.cgroup entries
PASS: No legacy 'lxc.cgroup' keys found.
INFO: Checking if the suite for the Debian security repository is correct..
PASS: found no suite mismatch
INFO: Checking for existence of NVIDIA vGPU Manager..
PASS: No NVIDIA vGPU Service found.
INFO: Checking bootloader configuration...
SKIP: not yet upgraded, no need to check the presence of systemd-boot
SKIP: No containers on node detected.

= SUMMARY =

TOTAL:    33
PASSED:   29
SKIPPED:  4
WARNINGS: 0
FAILURES: 0

Hat man eine ältere PVE Installation die schon von Version 6 auf 7 gepatcht hat oder sogar noch älter ist so kann es vor kommen das es ein Warning gibt bezüglich des NTP Services. Wird systemd-timesyncd eingesetzt so sollte man dies ändern. Endlich ist die Welt drauf gekommen das dies ein scheiss Service ist. PVE verwendet aktuell als Standard Chrony.

apt install chrony

vim /etc/chrony/chrony.conf

Hier kann man die gewünschten NTP Server eintragen.

Checken ob die NTP Verbindung richtig funktioniert kann man mit
chronyc tracking
chronyc sources

Bekommt man diese Warnung liegt das auch daran das man sein System schon länger bereibt.
Hier kann man auf einer Node im Cluster die Storage.cfg editieren

vim /etc/pve/storage.cfg

...
...
maxfiles 5
...

Hier einfach maxfiles 5 gegen prune-backups 5 ersetzten.