ID(1) General Commands Manual Fully-rendered PDF

id — get credentials

id [user]…
id -u|-g|-G [-nrz] [user]…
id -Z [-z]
groups [user]…
whoami

The flag-free form writes users' (each of which can either be a name or a numeric ID; if none specified — the process') credentials to the standard output stream:

uid=0(root) gid=0(root) groups=0(root(wheel),22 context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
uid=1000(cicada) gid=100(users) euid=0(root) egid=39(irc) groups=100(users),4(adm),27(sudo)
When an ID is missing from passwd(5) or group(5) its name and parentheses are omitted.

The IDs listed are real; and , containing the effective IDs, are only written if they differ.

If one of -ugGZ is specified, the IDs are effective by default, and only the specified field is output, numerically. For example, those very same invocations, but with -G and -u respectively:

0 10 22
0
And with -rn:
root wheel 22
cicada
In this mode, unknown groups are written as numbers and a diagnostic is issued.

The set of supplementary groups is sorted, but always starts with the primary group.

An unknown user is not a fatal error — a diagnostic is issued and processing continues.

The mandatory access control context is omitted from the default format if unavailable or unset, and -Z is forbidden if it's unavailable; additionally, as it's a property of the process, not user, it's only available if no user was specified.

, --user
Write just the user ID.
, --group
Write just the primary group ID.
, --groups
Write just the secondary group IDs.
, --context
Write just the security context.

, --name
Write the specified field as a human-readable name, rather than numerical ID.
, --real
Use the real user or primary group ID of the process, rather than the effective one. No effect with users.
, --zero
Terminate each entry with a NUL character, rather than a single space or newline.

Ignored for compatibility with the illumos gate, whose default id requires it to write the supplementary groups. (But the version from AT&T research dated 2004 also just ignores it.)

if at least one user or group wasn't on file.

who(1), getegid(2), getgroups(2), getuid(2), getgrouplist(3), getgwgid(3), getpwuid(3), selinux(8)

id conforms to IEEE Std 1003.1-2024 (“POSIX.1”).

Mandatory access control behaviour (-Z, context=) is compatible with the GNU system, though the latter deviates from the standard if a context is present; this is not considered a problem, as -ugG is recommended by the standard for noninteractive use, and scripts relying on the default CB-UNIX-style output already filter it.

-za and multiple users are extensions, also present on the GNU system.

The ordering of supplementary groups is not guaranteed.

whoami first appeared in 2BSD as whoami(UCB), noting:

It works even if you are su'd, while 'who am i' does not since it uses /etc/utmp.

groups appeared in 4.1cBSD as groups(1):

groups - show group memberships
with no arguments and present-day output, which also described the system's general group handling.

4.2BSD allows one user, as present-day.

id first appeared in CB-UNIX at or before version 2.1, using the familiar

uid=1000(user) gid=100(users) euid=0(root) egid=0(wheel)
format, with the notable exception of auxilliary groups, which originate from the BSD. CB-UNIX was, among others, the basis for AT&T System III UNIX, where it first saw light outside AT&T.

4.4BSD was the first to include id, quoting conformance with IEEE Std 1003.2 (“POSIX.2”), including the

100(users),0(wheel)
entry and -p extension, deprecating groups and whoami, replacing them with shell wrappers.

Since coreutils 8.31 (2019-03-10), the GNU system allows multiple users for id, too.

July 7, 2024 voreutils 5a9f9f29