Users and Groups

Rpm >= 4.19 has native support for declarative user and group creation through integration with systemd’s sysusers.d. Packagers will only need to package a sysusers.d file for their custom users and groups in /usr/lib/sysusers.d and rpm will take care of the rest.

It’s also possible to declare sysusers.d entries manually with %add_sysuser macro in the context of the (sub-)package. The macro simply takes a sysusers.d line as arguments, such as %add_sysuser g mygroup 515. Using this method is not recommended on native systemd distributions.

Dependencies

Any non-root ownership in %files section (through %attr() or %defattr()) generates an automatic dependency on the named user and/or group. Similarly, packaged sysusers.d files create provides for the users and/or groups they create. This ensures correct installation when a package relies on user/group from another package.

By default the dependencies are hard requirements, but as this can be problematic when upgrading an existing distribution to rpm 4.19, it’s possible to weaken these into recommends-dependencies by setting %_use_weak_usergroup_deps macro to 1 during package builds.

Limitations

At this time, rpm only supports the u and g directives of sysusers.d format and ignores others. If other directives are needed, the package will need to call systemd-sysusers with the correct arguments manually.

Technical details

As the sysusers.d data is needed before it’s unpacked from the payload during installation, rpm encodes the relevant parts into the EVR string of generated user() and group() provides: the sysusers.d line is base64 encoded, with the input \0-padded as needed to avoid base64 ‘=’ padding in the output, which would be illegal in the EVR string. These are decoded and fed into systemd-sysusers during installation, passing --replace <path> and --root <path> as appropriate.

For example, the following sysusers.d line:

u dnsmasq - "Dnsmasq DHCP and DNS server" /var/lib/dnsmasq

…emits the following provides attached to the originating file:

user(dnsmasq) = dSBkbnNtYXNxIC0gIkRuc21hc3EgREhDUCBhbmQgRE5TIHNlcnZlciIgL3Zhci9saWIvZG5zbWFzcQAA
group(dnsmasq)

As systemd-sysusers implicitly creates a matching group for any created users, the group provide does not have an EVR here, only explicitly created groups will have the encoded sysusers.d line as EVR.

Non-systemd operating systems

On non-systemd platforms, it’s possible to use either systemd-standalone-sysusers as a drop-in solution, or rpm can be configured to use a custom script instead of systemd-sysusers for user and group creation by overriding %__systemd_sysusers macro in the main rpm configuration.

Such a script needs to read sysusers.d lines from the standard input and interpret these into calls native user and group creation tools as appropriate. The script needs to handle --root <path> argument for chroot installations - the script runs from outside of any possible chroot, and care must be taken to avoid changing the host in such a case.