How to dynamically disable/enable SystemD Messages while running Combustion scripts (e.g. for custom dialogs) ?

[jomeier]

Hi,

I created custom dialogs that ask users for application specific settings, that must be set during combustion phase on first boot. I created a custom script for that and named it

custom/scripts/14u-custom-dialog.sh

with recent SLE Micro 6 versions (> 6.0 selfinstall !) Systemd status messages render my dialogs useless (Image 1). I tried to set this kernel argument with EIB:

systemd.show_status=0

this parameter works a few seconds during initial boot but short before the combustion phase systemd status messages come back:

The systemd status message is continously written over the dialog :(

Together with a SUSE consultant I was able to create a custom SLE Micro 6 ISO image containing the "systemd.show_status=0" kernel parameter. This version works as expected (Image 2), but requires a custom build of SLE Micro :(

This screen looks as expected!

I'm not sure if Edge Image Builder misses to set kernel parameters on all necessary locations in the base ISO image or if SLE Micro 6 versions from 6.1 on have this problem. SLE Micro 6.0 did not show this behaviour.

Expected Behaviour:
SLE Micro 6 should take kernel parameters configured with EIB (or simply manually entered in GRUB!) during the whole installation phase and first boot.

Currently it seems as if some kernel parameters are hardcoded in new SLE Micro ISO Images.

Having custom dialogs during combustion phase is a GREAT feature and it should be possible to use them out of the box!

Content of my custom script, if somebody is interested, how to get it running with the "dialog" tool in the combustion phase:

#!/bin/sh
# These parameters are necessary to render the dialog correct.
export TERM=linux;
export LANG=en_US.UTF-8


ROLE=master1
SETTING1=hiho
SETTING2=hohi

exec 3>&1;

network_test() {
  response=$(
  dialog --title "Node specific settings" --form "" 0 0 0 \
    "Role:" 1 1 "$ROLE" 1 15 20 0 \
    "Setting 1:" 2 1 "$SETTING1" 2 15 20 0 \
    "Setting 2:" 3 1 "$SETTING2" 3 15 20 0 \
  2>&1 1>&3 \
  > /dev/tty1)
}

network_test

exec 3>&-;

Any help would be appreciated.

Thanks,
Josef

[e-minguez]

I've not tested this but I remember from long time ago that back in the day when using kickstart, I used some tricks like these. See for example https://www.reddit.com/r/CentOS/comments/6mhagc/comment/dk1kmxn/
The trick there is changing the tty like:

exec < /dev/tty6 > /dev/tty6 2> /dev/tty6
chvt 6
# do the thing
# change back
chvt 1
exec < /dev/tty1 > /dev/tty1 2> /dev/tty1

That way I think you can avoid the systemd.show_status=0 parameter.

Again, I didn't tested this so perhaps doesn't even work

[jomeier]

I will try out your hack. Is this officially supported by the SLE Micro devs? I don't like to things get broken in future OS versions just because we are using an undocumented feature.

[e-minguez]

I will try out your hack. Is this officially supported by the SLE Micro devs? I don't like to things get broken in future OS versions just because we are using an undocumented feature.

Well, first of all, EIB just moves the custom scripts so they are executed via combustion https://documentation.suse.com/sle-micro/6.2/html/Micro-deployment-selfinstall-images/index.html#deployment-configuring-with-combustion and https://github.com/openSUSE/combustion?tab=readme-ov-file .

Combustion doesn't specify what is supported or not, it just runs some scripts in a transactional-update shell.

chvt is a cli that is included on the kbd package https://build.opensuse.org/projects/X11:XOrg/packages/kbd/files/kbd.spec?expand=1 and exec is a bash builtin.

[jomeier]

@e-minguez:
After vacation time I tried your idea yesterday but it seems not to work.

Maybe it is related to this idea from the systemd github repo:
systemd/systemd#9899

I have no idea how I can suppress this systemd status messages without setting a kernel argument (which is ignored by Edge Image Builder / hardcoded in the SLE Micro ISO image).

This is rather limiting the use cases of the combustion phase in my opinion.

[jomeier]

@e-minguez:
Ha! I found the solution to dynamically turn off/on systemd boot messages:

Write this in a SLE Micro combustion custom script and hand it over to Edge Image Builder:

# Set "systemd.show_status=0"
kill -SIGRTMIN+21 1

# Do something
...

# Set "systemd.show_status=1"
kill -SIGRTMIN+20 1

"kill -SIGRTMIN+21 1" sends a realtime signal to systemd (PID 1?) to turn off messages.
"kill -SIGRTMIN+20 1" sends a realtime signal to systemd (PID 1?) to turn on messages again

My initial problem is fixed and systemd messages can dynamically turned on/off now without the need of a reboot!

[jomeier]

Maybe this should find a way in the official documentation of Edge Image Builder ?