id

Display current user's ID (UID), group ID (GID), and groups to which they belong

$ id

$ id [[-un|--user --name]]

$ id [[-u|--user]]

$ id [[-gn|--group --name]]

$ id [[-g|--group]]

$ id [[-Gn|--groups --name]]

$ id [username]

$ id +[uid_number]

id [OPTION]... [USERNAME]

-a, --all
    print all (ignored in recent versions)

-G, --group
    print all group IDs

-g, --gid
    print effective group ID

-n, --name
    use names instead of numbers (with -G, -g, -u)

-r, --real
    print real ID instead of effective (with -g, -u)

-u, --uid
    print effective user ID

-Z, --context
    print SELinux security context

--help
    display help and exit

--version
    output version information and exit

The id command prints the real and effective user and group IDs, as well as supplementary group IDs, for the specified username or the current user if none is provided. It retrieves this information from the system's password and group databases using system calls like getuid(), getgid(), and getgroups().

Without options, id outputs a line in the format:
uid=NUM(username) gid=NUM(groupname) groups=NUM(groupname),NUM(groupname),...
where NUM are numeric IDs and names are resolved from /etc/passwd and /etc/group.

Options allow customization: numeric-only output, names only with -n, specific IDs with -u (user), -g (group), or all groups with -G. The -r flag shows real IDs instead of effective ones, useful in setuid/setgid contexts. SELinux users can print security contexts with -Z or --context.

This command is essential for scripting, debugging permissions, and verifying effective identities in processes. It works for any user without special privileges, as ID info is publicly queryable.

Output for other users may not show effective IDs if not running as that user; real IDs are always shown unless -r is used. SELinux context requires SELinux support.

id
uid=1000(alice) gid=1000(alice) groups=1000(alice),4(adm),24(cdrom),27(sudo)
id -Gn
alice alice adm cdrom sudo

0 if OK, 1 if errors (e.g., unknown user)

Originated in POSIX.1-2001; part of GNU coreutils since early versions. Enhanced with SELinux support in coreutils 6.11 (2007). Widely available on Unix-like systems.

whoami(1), groups(1), getent(1), logname(1)