[systemd-devel] systemd-sysusers

Zbigniew Jędrzejewski-Szmek zbyszek at in.waw.pl
Mon Feb 5 18:31:22 UTC 2018

On Mon, Feb 05, 2018 at 10:21:17AM -0800, Johannes Ernst wrote:
> > On Feb 4, 2018, at 21:56, Michael Chapman <mike at very.puzzling.org> wrote:
> > 
> > On Mon, 5 Feb 2018, Johannes Ernst wrote:
> >> It appears systemd-sysusers does not create home directories. On the other hand, it picks (largely unpredictable) UIDs from a range.
> >> 
> >> So I have to run systemd-sysusers, and after that, find the UID of the user and chown the home directory? Or is there the equivalent of the “useradd -m” flag somewhere that I’m just not seeing?
> > 
> > systemd-sysusers is, as the name suggests, really for _system_ users, and often those kinds of users don't have ordinary home directories -- that is, ones the user can actually write to.
> I agree with the “often” but not more :-)
> > However, systemd-sysusers.service is ordered before systemd-tmpfiles-setup.service at boot, so if you need to create a system user's home directory and ensure its ownership is correct, you could use a corresponding tmpfiles.d fragment to do so.
> Hmm … tmpfiles.d, according to its man page, is for “the creation, cleaning and removal of volatile and temporary files and directories which usually reside in directories such as /run or /tmp.”. That doesn’t really seem to cover home directories that contain actual data.
> Here’s my use case: Take a package for a daemon foo. The package contains a foo.service, and when foo runs, it is supposed to run in its own little place /var/lib/foo where it stores its data files. Because not everybody runs foo, it doesn’t make sense to pick a “fixed” UID like for more common daemons. Allocating a UID from a pool, like sysusers does, seems perfect. But how does the package ship /var/lib/foo? It can’t ship with owner foo because we don’t know what its UID is going to be. So the package, as part of its install script, needs to do something like:
> systemd-sysusers
> [[ -d /var/lib/foo ]] && mkdir -m755 /var/lib/foo
> chown $(id -u foo):$(id -g foo) /var/lib/foo

# /usr/lib/tmpfiles.d/foo.conf
d /var/lib/foo 0755 foo foo -

(BTW, chown $(id -u foo):$(id -g foo) ... is the same as chown foo:foo ...).


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