projid man page
projid — the project name mapping file
The /etc/projid file provides a mapping between numeric project identifiers and a simple human readable name (similar relationship to the one that exists between usernames and uids). Its format is simply:
# comments are hash-prefixed # ... cage:10 logfiles:42
This file is optional, if a project identifier cannot be mapped to a name, it will be parsed and displayed as a numeric value.
xfs_quota(8), xfsctl(3), projects(5).