Just yesterday, I received a task to install a software on our client's private/local server at their office. They were using Proxmox to create Containers (Virtual Machines) on it. However, as they were using Proxmox version 6.4-15 at that time and it had some issues, and we needed a feature available in version 7.x, I decided to perfom an upgrade.

The upgrade procedure was already provided by Proxmox, and you can find it here.

However, a new issue suddenly arose; the upgrade process stopped and got stuck at 57%. I started searching for a solution online and found a forum discussion (you can check it out here) with a similar issue. There, I got a hint: "kill the memtest".

You can press Ctrl+C on the ongoing upgrade process or do it through SSH on other device (laptop/computer in the same network). Type the command ps af, and you'll get something similar to the output below:

root@pvemadukara:~# ps af
  PID TTY      STAT   TIME COMMAND
30509 pts/2    Ss     0:00 -bash
  945 pts/2    R+     0:00  \_ ps af
 8419 pts/0    Ss     0:00 -bash
 6954 pts/0    S+     0:01  \_ apt dist-upgrade
27585 pts/1    Ss+    0:00      \_ /usr/bin/dpkg --status-fd 23 --configure --pending
27586 pts/1    S+     0:00          \_ /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/memtest86+.postin
27595 pts/1    Z+     0:00              \_ [memtest86+.post] <defunct>
 2308 tty1     Ss+    0:00 /sbin/agetty -o -p -- \u --noclear tty1 linux
root@pvemadukara:~#

Here you can see the line containing memtest86+.postin, and the PID is 27586. So, I killed the process with the following command:

kill 27586

Alhamdulillah, the installation process resumed and completed without any errors. After that, just reboot the server and you're done. Hope this helps!