systemd.image-filter — Disk Image Dissection Filter
In systemd, whenever a disk image (DDI) implementing the Discoverable
Partitions Specification is activated, a filter may be specified controlling which partitions to
consider for mounting. Such a disk image dissection filter is a string that contains per-partition-type
patterns, separated by colons (":"). The individual rules consist of a partition
identifier, an equal sign ("="), and a shell globbing pattern applied to the GPT label
string of the partition. See glob(7) for
details on shell globbing.
The partition identifiers currently defined are: root, usr,
home, srv, esp, xbootldr,
swap, root-verity, root-verity-sig,
usr-verity, usr-verity-sig, tmp,
var. These identifiers match the relevant partition types in the Discoverable Partitions
Specification, but are agnostic to CPU architectures.
Various systemd components that support operating with disk images support a
--image-filter= command line option to specify the image filter to use. If no filter is
specified all partitions in partition table are considered and no per-label filtering is applied (except
that partitions with the "_empty" label are always ignored).
For the host root file system image itself
systemd-gpt-auto-generator(8)
is responsible for processing the GPT partition table and making use of the included discoverable
partitions. It accepts an image filter via the kernel command line option
systemd.image_filter=.
The following image filter string dictates that for the root file system partition only partitions
shall be considered whose label begins with "ParticleOS-". For the
/usr/ partition the precise label "ParticleOS_47110815" is
required.
root=ParticleOS-*:usr=ParticleOS_47110815