Re: [systemd-devel] Required kernel version for pid1 only?

[林自均]

Hi Zbyszek and Mantas,

I got it. Thank you for the detailed answers.

John Lin

Mantas Mikulėnas  於 2018年1月9日 週二 下午4:23寫道：

> On Tue, Jan 9, 2018 at 10:10 AM, 林自均  wrote:
>
>> Hi folks,
>>
>> I saw the following lines in README:
>>
>> > REQUIREMENTS:
>> > Linux kernel >= 3.13
>> > Linux kernel >= 4.2 for unified cgroup hierarchy support
>>
>> I guess it means that some part of the whole systemd project requires
>> Linux kernel 3.13. What if I don't need that part and only pid1 is relevant
>> to me? Is such information provided somewhere?
>>
>
> There's no full list. You can only check commit logs to find out why the
> requirement was bumped (git log -p README), but once the new dependency is
> published, it's always possible that other parts of systemd code will start
> implicitly depending on *other* kernel features available in that release.
>
> For example, here's what prompted each bump:
>
> 3.13 - DM_DEFERRED_REMOVE (dcce98a4bdc3)
> 3.12 - %P in core_pattern (58015d7815bc)
> 3.11 - arbitrary (a0c3e16b7bce)
> 3.7 - kernel-based firmware loading (be2ea723b1d0)
> 3.0 - cgroup.procs (e946948eff51)
> 2.6.39 - oh come on
>
> ~
>
> In short, if it says "REQUIREMENTS: Linux ≥ 3.13", that's what you need to
> use. Anything below that is at your own risk.
>
> --
> Mantas Mikulėnas
>
___
systemd-devel mailing list
systemd-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/systemd-devel

Re: [systemd-devel] Required kernel version for pid1 only?

[Mantas Mikulėnas]

On Tue, Jan 9, 2018 at 10:10 AM, 林自均  wrote:

> Hi folks,
>
> I saw the following lines in README:
>
> > REQUIREMENTS:
> > Linux kernel >= 3.13
> > Linux kernel >= 4.2 for unified cgroup hierarchy support
>
> I guess it means that some part of the whole systemd project requires
> Linux kernel 3.13. What if I don't need that part and only pid1 is relevant
> to me? Is such information provided somewhere?
>

There's no full list. You can only check commit logs to find out why the
requirement was bumped (git log -p README), but once the new dependency is
published, it's always possible that other parts of systemd code will start
implicitly depending on *other* kernel features available in that release.

For example, here's what prompted each bump:

3.13 - DM_DEFERRED_REMOVE (dcce98a4bdc3)
3.12 - %P in core_pattern (58015d7815bc)
3.11 - arbitrary (a0c3e16b7bce)
3.7 - kernel-based firmware loading (be2ea723b1d0)
3.0 - cgroup.procs (e946948eff51)
2.6.39 - oh come on

~

In short, if it says "REQUIREMENTS: Linux ≥ 3.13", that's what you need to
use. Anything below that is at your own risk.

-- 
Mantas Mikulėnas
___
systemd-devel mailing list
systemd-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/systemd-devel

Re: [systemd-devel] Required kernel version for pid1 only?

[Zbigniew Jędrzejewski-Szmek]

On Tue, Jan 09, 2018 at 08:10:55AM +, 林自均 wrote:
> Hi folks,
> 
> I saw the following lines in README:
> 
> > REQUIREMENTS:
> > Linux kernel >= 3.13
> > Linux kernel >= 4.2 for unified cgroup hierarchy support
> 
> I guess it means that some part of the whole systemd project requires Linux
> kernel 3.13. What if I don't need that part and only pid1 is relevant to
> me? Is such information provided somewhere?
Generally it's pid1 that has the strongest requirements. Sometimes
we need a specific system call, in which case the requirement applies
to library code and all of the project.

Usually you can find _why_ this specific version is required by
looking at the commit that raised the requirement in docs, it should
contain a brief justification. But it's not guaranteed to list all the
reasons, and new uses could have been added in the meantime, and as
long as the latest required kernel version supports them, this
wouldn't be mentioned anywhere. It should be possible to compile and
use systemd with older kernel versions using some workarounds or by
omitting features, but this is not supported and you're basically on
your own.

Zbyszek
___
systemd-devel mailing list
systemd-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/systemd-devel

[systemd-devel] Required kernel version for pid1 only?

[林自均]

Hi folks,

I saw the following lines in README:

> REQUIREMENTS:
> Linux kernel >= 3.13
> Linux kernel >= 4.2 for unified cgroup hierarchy support

I guess it means that some part of the whole systemd project requires Linux
kernel 3.13. What if I don't need that part and only pid1 is relevant to
me? Is such information provided somewhere?

Thanks.

John Lin
___
systemd-devel mailing list
systemd-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/systemd-devel