Re: [PATCH 3/3] image-postproc-extension: add removal of machine-id

[Claudius Heine <claudius.heine.ext@siemens.com>]

Hi Henning,

On 28/05/2019 19.44, Henning Schild wrote:
> Am Tue, 28 May 2019 10:58:14 +0200
> schrieb "[ext] claudius.heine.ext@siemens.com"
> <claudius.heine.ext@siemens.com>:
> 
>> From: Claudius Heine <ch@denx.de>
>>
>> The machine-id(5) should contain a unique id of the machine, but since
>> this file is created by the systemd postinst script, every machine
>> using the same image would have the same id.
>>
>> The file is removed in a postprocessing step and will be regenerated
>> by systemd on the first boot.
> 
> Systemd is not the only officially supported init system on Debian. And
> i disagree with anyone claiming that it is OK to assume that in Isar ;).
> 
> I just did a little test and the outcome means we need more research.
> 
> In stretch with sysvinit-core in IMAGE_PREINSTALL there will be no
> machine-id. So it is OK to rm -f, where the f is important.
> 
> In buster there is one, no clue where it comes from ... But that is
> not magically recreated at first boot. Meaning we might have deleted an
> important file without a plan to bring it back.
> 
> Question is, is it important at all for !systemd. If not at all, who
> created and and why? Btw ... my gentoo laptop also has one, and i would
> never install systemd. Maybe udev ...

 From machine-id(5):
        The machine ID is usually generated from a random source during 
system
        installation or first boot and stays constant for all subsequent 
boots.
        Optionally, for stateless systems, it is generated during 
runtime during early
        boot if necessary.

As I understand it, it is ok to remove that file if the system has 
technically not booted yet. Systemd also couples its 'first boot 
detection' on the existence of the `/etc/machine-id` file:

 From systemd.unit(5):
            ConditionFirstBoot= takes a boolean argument. This condition 
may be used to
            conditionalize units on whether the system is booting up 
with an unpopulated
            /etc directory (specifically: an /etc with no 
/etc/machine-id). This may be
            used to populate /etc on the first boot after factory reset, 
or when a new
            system instance boots up for the first time.

So any system that depends on the existence of a machine-id should also 
depend on systemd (or something else) recreating that on the first boot 
if it does not exist.

Claudius

> 
> Henning
> 
>> Signed-off-by: Claudius Heine <ch@denx.de>
>> ---
>>   meta/classes/image-postproc-extension.bbclass | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/meta/classes/image-postproc-extension.bbclass
>> b/meta/classes/image-postproc-extension.bbclass index
>> 625ba7d..495eae6 100644 ---
>> a/meta/classes/image-postproc-extension.bbclass +++
>> b/meta/classes/image-postproc-extension.bbclass @@ -26,8 +26,7 @@
>> update_etc_os_release() { fi
>>   }
>>   
>> -ROOTFS_POSTPROCESS_COMMAND =+ "image_postprocess_configure
>> image_postprocess_mark" -
>> +ROOTFS_POSTPROCESS_COMMAND =+ "image_postprocess_configure"
>>   image_postprocess_configure() {
>>       # Configure root filesystem
>>       if [ -n "${DISTRO_CONFIG_SCRIPT}" ]; then
>> @@ -39,8 +38,16 @@ image_postprocess_configure() {
>>      fi
>>   }
>>   
>> +ROOTFS_POSTPROCESS_COMMAND =+ "image_postprocess_mark"
>> +
>>   image_postprocess_mark() {
>>       BUILD_ID=$(get_build_id)
>>       update_etc_os_release \
>>           --build-id "${BUILD_ID}" --variant "${DESCRIPTION}"
>>   }
>> +
>> +ROOTFS_POSTPROCESS_COMMAND =+ "image_postprocess_machine_id"
>> +image_postprocess_machine_id() {
>> +    # systemd(1) takes care of recreating the machine-id on first
>> boot
>> +    sudo rm -f '${IMAGE_ROOTFS}/etc/machine-id'
>> +}
> 

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