Symptoms

An error occurs while trying to create cache or update cache for the ubuntu-20.04-x86_64 EZ template for containers with:

vzpkg create cache ubuntu-20.04-x86_64

OR

vzpkg update cache ubuntu-20.04-x86_64

The resulted error is:

Errors were encountered while processing:
apt
E: Sub-process /usr/bin/dpkg returned an error code (1)
Error: /usr/bin/apt-get failed, exitcode=100
Error: Failed to umount ploop image /vz/tmp//vzpkg.zvESPm/cache-private/root.hdd: Error in ploop_umount_image (ploop.c:2807): Image /vz/tmp/vzpkg.zvESPm/cache-private/root.hdd/root.hds is not mounted 40

Cause

The issue is recognized as product bug PSBM-140305, error is caused by specific version of apt package - 2.0.8, which has a bug in post-installation script.

Resolution

The issue has been fixed in the Virtuozzo Hybrid Server 7.5 Update 3 Hotfix 2 (7.5.3-407)

Update your Virtuozzo Hybrid Server 7 to the latest version and repeat the cache creation/update for ubuntu-20.04-x86_64 EZ template.