Acronym for User ID.
The numerical id that corresponds to a user. For example 0 is usually root. bobs UID might be 500. UID to name mappings are stored in /etc/passwd (see passwd(5))
- Set UID (SUID)
- A program is said to be "SUID" when the file has the "+s" user permission bit set, so the program will run as the permissions of the user that owned the file, not the user that ran the file.
- Actual UID
- The uid listed in your auth mechanism against the username you logged in as. Alternatively, the uid a process was launched by, as opposed to the uid it runs as (the EUID)
- Effective UID (EUID)
- The user that a programs permission checks are done against. This is often root if you run a SUID program. The Actual UID is your normal UID, but the effective UID is that of root.