Problem
On Data Protector (DP) Linux systems, using systemd, we see the following...
 - systemctl status State: degraded.
 - and `systemctl` reports errors including...
       loaded failed failed DATA-PROTECTOR-INET

Background
Since Data Protector version 10.70 (also known as version 2020.05) the use of systemd is supported on the Cell Manager and Clients.
When systemd is used the xinetd package is no longer required.

However the support of systemd is only for RHEL 8.0 and later versions and SLES 15 and later versions.   For those supported versions there is a patch available.

For other versions of Linux, Data Protector still requires the xinetd package.

Credit to @Scorpio_CZ for his help in the analysis of this problem.

Solution

For DP systems which are not RHEL 8.0 (or later versions) or SLES 15 (or later versions)...

Uninstall DP from the linux system.

If the linux system was installed locally please uninstall by `cd` to the LOCAL_INSTALL directory and    remove DP with `./omnisetup.sh -Delete`
Check the 3 directories (/opt/omni,/etc/opt/omni and /var/opt/omni) are all empty...
Remove the directories.
Reboot the server (if possible).
Ensure xinetd is installed and active on the system.
After that re-install DP to the system so it will use xinetd.

If the linux system was installed using an Installation Server,  with the DP GUI, Clients context, Right click on the client hostname an select "Delete".
It says "Do you also want to uninstall the Data Protector software?" and select "Yes".
DP removes the software from the client and also details of the client from the DP CM.
Optional: Reboot the linux server (if possible).
Ensure xinetd is installed and active on the system.
After that re-install DP to the system, so it will use xinetd.

For DP systems which are RHEL 8.0 (or later versions) or SLES 15 (or later versions)...

contact HP support and request DP1070_b210_OCTCR19Q970054_HF4_ux.

As DP1070_b210_OCTCR19Q970054_HF4_ux contains inet code it must be installed manually.
Do not try to use an Installation Server (IS) to install the patch.

To install (manually)...
When there is no Data Protector activity on the linux client make safe backup copies of the existing
/opt/omni/lbin/inet
/opt/omni/lbin/fsbrda
binaries (so roll back is possible if required).

Copy from the extracted DP1070_b210_OCTCR19Q970054_HF4_ux.tar.gz
<PATH>\A.10.70\CORE\opt\omni\lbin\inet
<PATH>\A.10.70\DA\opt\omni\lbin\fsbrda
to
/opt/omni/lbin/inet
/opt/omni/lbin/fsbrda
on the client.

Copy from the extracted DP1070_b210_OCTCR19Q970054_HF4_ux.tar.gz
<PATH>\A.10.70\CORE\etc\opt\omni\client\ssptm\CII_OCTCR19Q970054_HF4
to
/etc/opt/omni/client/ssptm

You may have to create the ssptm directory.

The value of the source <PATH> will vary depending on the linux version installed on the client.

Other information.

There is an equivalent patch available for DP 10.80.  (DP1080_b134_OCTCR19Q970054_HF1)

The code within DP1070_b210_OCTCR19Q970054_HF4_ux is included in General Release DP 10.90

This DP/systemd Linux Operating System limitation is documented in the  DP 10.80 and 10.90

DP 10.70...
https://docs.microfocus.com/itom/Data_Protector:2020.05/ReleaseNotes
DP 10.80...
https://docs.microfocus.com/itom/Data_Protector:2020.08/ReleaseLog
DP 10.90...
https://docs.microfocus.com/itom/Data_Protector:2020.11/ReleaseLog
DP 10.91...
https://docs.microfocus.com/itom/Data_Protector:2021.02/ReleaseLog

Note: systemd is supported on RHEL 8.0 and later versions, and on SLES 15 and later versions.

Confirming with the command line that the patch has been installed.

On the Cell Manager run 

`omnicheck -ssphf -host <hostname of client>`

and you should see...

Site Specific Patch / HotFix         Status
========================================================
OCTCR19Q970054_HF4                        Installed
Number of SSPs and HFs found: 1.
 

Why an Installation Server (IS) can not be used to install this patch.

DP code that must be changed for a patch must not be in use at the time it is changed.
Most patches for DP clients can be installed using an IS if the code being changed is not in use.
This patch (DP1070_b210_OCTCR19Q970054_HF4_ux) contains an inet binary however, and
inet is a process required to change the code on the client.
So, unfortunately, this patch cannot be installed using an IS.
No patch containing inet can be installed with an IS.