projects man page
projects — persistent project root definition
The /etc/projects file provides a mapping between numeric project identifiers and those directories which are the roots of the quota tree. Its format is simply:
# comments are hash-prefixed # ... 10:/export/cage 42:/var/log
The /etc/projects file is optional, instead xfs_quota(8) can be used with the -p argument to specify a project root directly for each operation.
xfs_quota(8), xfsctl(3), projid(5).