[OE-core] [OE-Core][PATCH v6 0/6] systemd stateless configuration

[Jonas Bonn]

Hi Alex,

On 03/05/2019 10:37, Alex Kiernan wrote:
> On Thu, May 2, 2019 at 10:10 PM Alex Kiernan <alex.kiernan at gmail.com> wrote:
>>
>>
>> This patch set is largely Jonas Bonn's to move towards a "stateless"
>> configuration:
>>
>>    These patches make some modifications to systemd with the long-term goal
>>    of being able to run OE in systemd's "stateless" configuration.
>>    "Stateless" boils down to building an image with empty /etc and /var
>>    directories so that volatile (tmpfs) filesystems can be mounted there;
>>    this requires that the system subsequently be able to populate these
>>    directories dynamically, which systemd mostly takes care of if things are
>>    done right.
>>
>>    In these patches:
>>    i)   Don't include machine-id in writable images so that systemd can run
>>         its first-boot machinery
>>    ii)  Move systemd configuration files out of /etc
>>    iii) Allow systemd to dynamically enable services and populate
>>         /etc/systemd/system via the presets mechanism
>>
>>    There's a long way to go to get to a working "stateless" configuration.
>>    Getting to a "volatile" system (just empty /var) should be easier and I'll
>>    post patches moving things in that direction shortly.
>>
>> However as a result of the systemd 242 upgrade, which includes 01d2041e41f4
>> ("meson: stop creating enablement symlinks in /etc during installation"),
>> services such as systemd-networkd are no longer enabled in images.
>>
>> This patch set fixes this problem in addition to satisfying the goal of
>> moving towards "stateless" configurations.
>>
>> The issue with respect to image testing during CI was caused by
>> systemd-time-wait-sync.service being enabled due to the lack of a default
>> preset policy:
>>
>> https://www.freedesktop.org/wiki/Software/systemd/Preset/#howto
>>
>> Changes in v6:
>> - switch configuration to simple overrides in /usr/lib/systemd/*.conf.d
>> - make systemd RRECOMMENDS rather than RDEPENDS on systemd-conf
>> - don't exit in postinst as when that executes we're actually a
>>    concatenation of all fragments
>> - validate SYSTEMD_AUTO_ENABLE is `enable` or `disable`
>> - rewrite systemctl-native in Python
>> - moved systemctl preset-all to IMAGE_PREPROCESS so it runs after ROOTFS,
>>    run for all images, not just read-only
>>
>> Changes in v5:
>> - rebased for systemd 242
>> - install default preset distribution policy of "enable nothing"
>>
>> Alex Kiernan (3):
>>    systemd-conf: simplify creation of machine-specific configuration
>>    systemctl-native: Rewrite in Python supporting preset-all and mask
>>    image: call systemctl preset-all for images
>>
>> Jonas Bonn (3):
>>    systemd: don't build firstboot by default
>>    systemd: do not create machine-id
>>    systemd: create preset files instead of installing in image
>>
>>   meta/classes/image.bbclass                    |   9 +-
>>   meta/classes/rootfs-postcommands.bbclass      |   6 +
>>   meta/classes/systemd.bbclass                  |  41 +-
>>   .../systemd/systemd-conf/journald.conf        |   3 +
>>   .../systemd/systemd-conf/logind.conf          |   2 +
>>   .../systemd/systemd-conf/system.conf          |   2 +
>>   .../systemd/systemd-conf/system.conf-qemuall  |   3 +
>>   meta/recipes-core/systemd/systemd-conf_242.bb |  61 +--
>>   .../systemd/systemd-systemctl/systemctl       | 476 ++++++++++--------
>>   .../systemd/systemd/99-default.preset         |   1 +
>>   meta/recipes-core/systemd/systemd_242.bb      |  26 +-
>>   11 files changed, 360 insertions(+), 270 deletions(-)
>>   create mode 100644 meta/recipes-core/systemd/systemd-conf/journald.conf
>>   create mode 100644 meta/recipes-core/systemd/systemd-conf/logind.conf
>>   create mode 100644 meta/recipes-core/systemd/systemd-conf/system.conf
>>   create mode 100644 meta/recipes-core/systemd/systemd-conf/system.conf-qemuall
>>   create mode 100644 meta/recipes-core/systemd/systemd/99-default.preset
>>
> 
> Sigh...
> 
> this still has issues - if you boot with `ro` on the kernel command
> line and without an initramfs, then / is read-only when systemd starts
> and it basically refuses to do anything:
> 
> [    7.222134] systemd[1]: No hostname configured.
> [    7.227266] systemd[1]: Set hostname to <localhost>.
> [    7.232622] systemd[1]: System cannot boot: Missing /etc/machine-id
> and /etc is mounted read-only.
> [    7.241750] systemd[1]: Booting up is supported only when:
> [    7.247362] systemd[1]: 1) /etc/machine-id exists and is populated.
> [    7.253752] systemd[1]: 2) /etc/machine-id exists and is empty.
> [    7.259757] systemd[1]: 3) /etc/machine-id is missing and /etc is writable.
> 
> Note this has nothing to do with read-only-rootfs, this is just a
> regular boot... that said a bunch of things that were broken now work,
> so it's progress!
> 
> I'm leaning towards having systemctl-native touch /etc/machine-id when
> it runs, unless you explicitly ask for stateless in DISTRO_FEATURES...
> patches to follow.

The paradigm that systemd follows is that /etc is _always_ writable. 
The read-only rootfs that OE produces with a read-only /etc is 
pathological from systemd's point of view (as is your 'ro' kernel 
parameter example).  The way to handle this is to:

i) mount a tmpfs over /etc
ii) move the contents of /etc to /usr/share/factory/etc at buildtime and 
have tmpfiles.d snippets that take care of populating /etc at runtime

I have a set of patches that does this, but it's all pretty fragile at 
this point in time.  It scans /etc at buildtime, moves files and links 
to factory/{var,etc}, sets up tmpfiles.d snippets for files and 
directories.  Doing this, however, somewhat requires for things that 
_can_ be set up at runtime to be so; what remains in /etc should only be 
stuff that doesn't set itself up at runtime _yet_.  For this reason, I'm 
inclined to say that you _don't_ want to leave the /etc/systemd/system 
nor /etc/machine-id files in the image.

/Jonas


> 
> --
> Alex Kiernan
>