Under Linux, every file is owned by exactly one user and one group. Every user has an identifying number, the User ID (UID). The same applies for a group: it is resolved by a Group ID (GID). Every user has exactly one UID and one primary GID; however, users can be members of multiple groups. In that case, the user will have one or more supplementary GIDs. You can see this for yourself by running the id command on your Ubuntu machine:
reader@ubuntu:~$ iduid=1000(reader) gid=1004(reader) groups=1004(reader),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lxd),1000(lpadmin),1001(sambashare),1002(debian-tor),1003(libvirtd)reader@ubuntu:~$
In the preceding output, we can see the following things:
- The uid for the
