systemd: systemctl show <service> prints "Failed to parse bus message: Invalid argument" before output (Debian Bug #964926) on Armbian Buster Current

[Marecki]

Hello,

 

In case you haven't heard about this yet, the fact that Armbian Buster Current comes with a 5.8 kernel means it suffers from this Debian bug:

 

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=964926

 

which us caused by combining this kernel version (as well as future ones) with systemd built using older kernel headers. This bug is mostly harmless but it does at the very least prevent Ansible from managing services on affected systems due to 'systemctl show' exiting with a non-zero exit code.

 

Unfortunately with the official Debian Buster kernel version being 4.19 it is unlikely that this will be fixed on their end.

[lanefu]

I've posted a workaround on here

 

https://github.com/ansible/ansible/issues/71528#issuecomment-687623381

[Marecki]

Unfortunately upgrading systemd to the version from buster-backports doesn't help, that version has apparently still been built using older kernel headers:

 

# systemctl --version
systemd 245 (245.6-1~bpo10+1)
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=hybrid
# systemctl show armbian-hardware-monitor.service >/dev/null
Failed to parse bus message: Invalid argument
# echo $?
1

 

(this is from a system which has been restarted several times since the systemd upgrade)

 

Downgrading the kernel obviously does help but it's a bit of a blunt instrument, especially if one wants to run Ansible regularly rather than just for initial set-up.

[Igor]

2 hours ago, Marecki said:

Downgrading the kernel obviously does help but it's a bit of a blunt instrument

Another option is to help fix the problem? We are unable to cover all problems that bumps up.

[lanefu]

4 hours ago, Marecki said:

Unfortunately upgrading systemd to the version from buster-backports doesn't help, that version has apparently still been built using older kernel headers:

 

Oh oops works on bullseye

 

Option 2 I posted in that github issue is to mask the CAP_BPF capability, I just wasn't able to figure out how

[Marecki]

On 9/15/2020 at 12:24 PM, Igor said:

Another option is to help fix the problem?

 

The "proper" solution, i.e. one which requires neither downgrading the kernel nor masking new capabilities, is pretty straightforward - recompile Buster systemd packages against Linux-5.8+ kernel headers. I thought my original explanation ("systemd built against kernel headers older than 5.8 does not work") made this clear, in hindsight I should have been more explicit.

Edited September 20, 2020 by Marecki