The Debian packages of the Agent2 plugins do not have a dependency on the agent2 package. When doing deployments via Ansible and specifying the agent2 package and 1 or more plugins, the order that Ansible tries to install the packages isn't controlled. If Ansible tries to install the plugin first, an error results when the plugin package tries to set the file permissions in the postinst script because the zabbix group does not exist. The zabbix group has to be installed first, so the zabbix-agent2 package has to be installed first. Without having the plugins depend on the agent2 package, this is not guaranteed.

Steps to reproduce:

1. Provide the agent2 and plugin packages to apt in an unexpected order:
2. sudo apt install zabbix-agent2-plugin-postgresql zabbix-agent2

Result:

 sudo apt install zabbix-agent2-plugin-postgresql zabbix-agent2

Installing:                     
  zabbix-agent2  zabbix-agent2-plugin-postgresql

Summary:
  Upgrading: 0, Installing: 2, Removing: 0, Not Upgrading: 1
  Download size: 9,261 kB
  Space needed: 30.1 MB / 10.7 GB available

Get:1 https://repo.zabbix.com/zabbix/8.0/unstable/debian trixie/main amd64 zabbix-agent2 amd64 2:8.0.0~rc2-1+debian13 [6,363 kB]
Get:2 https://repo.zabbix.com/zabbix/8.0/unstable/debian trixie/main amd64 zabbix-agent2-plugin-postgresql amd64 1:8.0.0~rc2-1+debian13 [2,898 kB]
Fetched 9,261 kB in 1s (9,494 kB/s)                        
Selecting previously unselected package zabbix-agent2.
(Reading database ... 40350 files and directories currently installed.)
Preparing to unpack .../zabbix-agent2_2%3a8.0.0~rc2-1+debian13_amd64.deb ...
Unpacking zabbix-agent2 (2:8.0.0~rc2-1+debian13) ...
Selecting previously unselected package zabbix-agent2-plugin-postgresql.
Preparing to unpack .../zabbix-agent2-plugin-postgresql_1%3a8.0.0~rc2-1+debian13_amd64.deb ...
Unpacking zabbix-agent2-plugin-postgresql (1:8.0.0~rc2-1+debian13) ...
Setting up zabbix-agent2-plugin-postgresql (1:8.0.0~rc2-1+debian13) ...
chown: invalid group: ‘root:zabbix’
dpkg: error processing package zabbix-agent2-plugin-postgresql (--configure):
 installed zabbix-agent2-plugin-postgresql package post-installation script subprocess returned error exit status 1
Setting up zabbix-agent2 (2:8.0.0~rc2-1+debian13) ...
Created symlink '/etc/systemd/system/multi-user.target.wants/zabbix-agent2.service' → '/usr/lib/systemd/system/zabbix
-agent2.service'.
Job for zabbix-agent2.service failed because the control process exited with error code.
See "systemctl status zabbix-agent2.service" and "journalctl -xeu zabbix-agent2.service" for details.
invoke-rc.d: initscript zabbix-agent2, action "start" failed.
● zabbix-agent2.service - Zabbix Agent 2
     Loaded: loaded (/usr/lib/systemd/system/zabbix-agent2.service; enabled; preset: enabled)
     Active: activating (auto-restart) (Result: exit-code) since Thu 2026-10-22 14:06:53 EDT; 32ms ago
 Invocation: 2f1aa79f354d4d08a349a04801bdc0f3
    Process: 1347 ExecStartPre=/usr/sbin/zabbix_agent2 -T -c $CONFFILE (code=exited, status=1/FAILURE)
   Mem peak: 7.2M
        CPU: 24ms
dpkg: error processing package zabbix-agent2 (--configure):
 installed zabbix-agent2 package post-installation script subprocess returned error exit status 1
Processing triggers for man-db (2.13.1-1) ...
Errors were encountered while processing:
 zabbix-agent2-plugin-postgresql
 zabbix-agent2
Error: Sub-process /usr/bin/dpkg returned an error code (1)

Expected:
Installation successful because apt configures zabbix-agent2 prior to configuring zabbix-agent2-plugin-postgresql due to zabbix-agent2-plugin-postgresql having a dependency on zabbix-agent2 defined in the deb package.