ID(1P)

💖 ID(1P) — POSIX Programmer's Manual 💖

okay bestie, we're doing id today and honestly? she's a baddie. she tells you who you are. like, literally. user identity reveal, main character energy 👑

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🎀 PROLOG 🎀

real talk first, bestie: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so go consult the corresponding Linux manual page for the deets on Linux behavior), or — plot twist — the interface may not be implemented on Linux at all. 💀

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✨ NAME ✨

id — return user identity

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🦋 SYNOPSIS 🦋

id [user]

id -G [-n] [user]

id -g [-nr] [user]

id -u [-nr] [user]

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🌸 DESCRIPTION 🌸

So, if you don't hand her a user operand, the id utility shall write the user and group IDs and the corresponding user and group names of the invoking process to standard output. invoking process = you, boo.

If the effective and real IDs do not match, both shall be written. No picking favorites.

And if multiple groups are supported by the underlying system (peep the description of {NGROUPS_MAX} in the System Interfaces volume of POSIX.1‐2017 for that one), then the supplementary group affiliations of the invoking process shall also be written. she's thorough like that 💅

Now — if a user operand is provided and the process has the appropriate privileges, then the user and group IDs of the selected user shall be written. In this case, effective IDs shall be assumed to be identical to real IDs (no drama, they're the same). And if the selected user has more than one allowable group membership listed in the group database, those shall be written in the same manner as the supplementary groups described in the paragraph above. ✨

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💅 OPTIONS 💅

The id utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines. (iconic behavior, truly)

The following options shall be supported:

• -G — Output all different group IDs (effective, real, and supplementary) only, using the format "%u\n". If there is more than one distinct group affiliation, output each such affiliation, using the format " %u", before the <newline> is output.
• -g — Output only the effective group ID, using the format "%u\n".
• -n — Output the name in the format "%s" instead of the numeric ID using the format "%u".
• -r — Output the real ID instead of the effective ID.
• -u — Output only the effective user ID, using the format "%u\n".

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🍓 OPERANDS 🍓

The following operand shall be supported:

• user — The login name for which information is to be written. (yes bestie, you can snoop on someone else, assuming privileges, we see you 👀)

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🧚 STDIN 🧚

Not used. she doesn't want your input here, she's got this 💜

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🌈 INPUT FILES 🌈

None. nothing to see, nothing to read.

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⭐ ENVIRONMENT VARIABLES ⭐

The following environment variables shall affect the execution of id:

• LANG — Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2017, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
• LC_ALL — If set to a non-empty string value, override the values of all the other internationalization variables. (she said what she said, absolute override)
• LC_CTYPE — Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).
• LC_MESSAGES — Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informative messages written to standard output.
• NLSPATH — Determine the location of message catalogs for the processing of LC_MESSAGES.

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🦄 ASYNCHRONOUS EVENTS 🦄

Default.

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👑 STDOUT 👑

The following formats shall be used when the LC_MESSAGES locale category specifies the POSIX locale. In other locales, the strings uid, gid, euid, egid, and groups may be replaced with more appropriate strings corresponding to the locale. (localization queen 🌍)

"uid=%u(%s) gid=%u(%s)\n", <real user ID>, <user-name>,
    <real group ID>, <group-name>

If the effective and real user IDs do not match, the following shall be inserted immediately before the '\n' character in the previous format:

" euid=%u(%s)"

with the following arguments added at the end of the argument list:

<effective user ID>, <effective user-name>

If the effective and real group IDs do not match, the following shall be inserted directly before the '\n' character in the format string (and after any addition resulting from the effective and real user IDs not matching):

" egid=%u(%s)"

with the following arguments added at the end of the argument list:

<effective group-ID>, <effective group name>

If the process has supplementary group affiliations or the selected user is allowed to belong to multiple groups, the first shall be added directly before the <newline> in the format string:

" groups=%u(%s)"

with the following arguments added at the end of the argument list:

<supplementary group ID>, <supplementary group name>

and the necessary number of the following added after that for any remaining supplementary group IDs:

",%u(%s)"

and the necessary number of the following arguments added at the end of the argument list:

<supplementary group ID>, <supplementary group name>

If any of the user ID, group ID, effective user ID, effective group ID, or supplementary/multiple group IDs cannot be mapped by the system into printable user or group names, the corresponding "(%s)" and name argument shall be omitted from the corresponding format string. (no name? no parentheses. simple as that.)

When any of the options are specified, the output format shall be as described in the OPTIONS section. 📎

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🙈 STDERR 🙈

The standard error shall be used only for diagnostic messages. she's not gonna spam your error stream for no reason, she has boundaries.

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🎀 OUTPUT FILES 🎀

None.

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💜 EXTENDED DESCRIPTION 💜

None.

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🔥 EXIT STATUS 🔥

The following exit values shall be returned:

• 0 — Successful completion. (slay, we ate)
• >0 — An error occurred. (not slay, something went wrong)

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😭 CONSEQUENCES OF ERRORS 😭

Default.

The following sections are informative. (i.e. the vibes, not the law ✨)

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🫶 APPLICATION USAGE 🫶

Output produced by the -G option and by the default case could potentially produce very long lines on systems that support large numbers of supplementary groups. 😳

(On systems with user and group IDs that are 32-bit integers and with group names with a maximum of 8 bytes per name, 93 supplementary groups plus distinct effective and real group and user IDs could theoretically overflow the 2048-byte {LINE_MAX} text file line limit on the default output case. It would take about 186 supplementary groups to overflow the 2048-byte barrier using id -G.)

This is not expected to be a problem in practice, but in cases where it is a concern, applications should consider using fold -s before post-processing the output of id. 💅

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🌸 EXAMPLES 🌸

None. (she said no examples, she's mysterious)

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🧠 RATIONALE 🧠

The functionality provided by the 4 BSD groups utility can be simulated using:

id -Gn [ user ]

The 4 BSD command groups was considered, but it was not included because it did not provide the functionality of the id utility of the SVID. Also, it was thought that it would be easier to modify id to provide the additional functionality necessary to systems with multiple groups than to invent another command. (why build new when you can upgrade? iconic decision-making)

The options -u, -g, -n, and -r were added to ease the use of id with shell commands substitution. Without these options it is necessary to use some preprocessor such as sed to select the desired piece of information. Since output such as that produced by:

id -u -n

is frequently wanted, it seemed desirable to add the options. ⭐

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🦋 FUTURE DIRECTIONS 🦋

None.

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👀 SEE ALSO 👀

fold, logname, who

The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

The System Interfaces volume of POSIX.1‐2017, getgid(), getgroups(), getuid()

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💖 COPYRIGHT 💖

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.

In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie!! brought to you by IEEE/The Open Group, 2017 — the original ID(1P) source and date, preserved forever in this cute little sign-off. go forth and id responsibly 🫶✨