Id command in Linux

Introduction

Before we discuss id command in Linux, let's briefly understand-What is id Command ?

The id command in Linux is used to retrieve information about the current user or specified user's identity and group memberships. It provides details such as User ID (UID), Group ID (GID), supplementary groups, and more. The id command is helpful for checking user permissions and diagnosing access-related issues.

id is a command-line tool that displays the current and valid user and group IDs.

In this tutorial, we will talk about the id command. We will also address a few FAQs on id command in Linux.

Using the id Command

The id command has the following syntax:

id [OPTIONS] [USERNAME]

The id command displays information about the currently logged-in user if the username is not specified.

id prints the real user ID (uid), the user's real primary group ID (gid), and the real IDs of the supplemental groups (groups) the user belongs to when run without any options. Only when the effective user ID, group ID, and supplemental group IDs differ from the true ones are they printed.

id

uid=1000(vegastack) gid=1000(vegastack) groups=1000(vegastack),4(adm),27(sudo),998(docker)

id additionally prints the user's security context (context) if SELinux is enabled:

uid=1000(vegastack) gid=1000(vegastack) groups=1000(vegastack) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

Pass the username or user ID as a parameter to the id command to get information about another user:

id mark

Output

uid=1001(mark) gid=1001(mark) groups=1001(mark),998(docker)

If the system already has a user with the same name as the supplied ID, the name look-up takes precedence. To avoid the ID being misinterpreted as a name, prefix it with the + sign when using it as an argument.

If you have a user with the name 1010 and another with the ID 1010, for example, typing id 1010 will reveal information about the user with the name 1010. Type id +1010 to get information about the user with ID 1010.

id Command Options

The id command has a number of arguments that allow you to display only certain data. When utilizing id in shell scripts, this is useful.

Use the -u (--user) option to print only the effective user ID:

id -u 

Output

1000

With the -g (--group) option, id will only print the effective group ID:

id -g

Output

1000 4 27 998

To print the effective IDs of all groups to which the user belongs, use the -G (--groups) option:

id -G

Output

1000

Use the -n, --name option to output names instead of numbers. This option can only be used in conjunction with the -u, -g, and -G options.

id -un

Output

vegastack

Running the id command with the -un parameters produces the same results as running whoami, and running id -Gn produces the same results as running groups.

The -r, (--real) option can be combined with the -u, -g, and -G options to output real numbers rather than effective values:

id -ur

Use the -Z (--context) option to print only the process's security context, which is normally the user's security context:

id -Z

Output

unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

id sends an error message if SELinux is disabled:

id: --context (-Z) works only on an SELinux-enabled kernel

The -z (--zero) option instructs id to use the NULL character instead of whitespace to delimit the output items:

id -znG

Output

vegastackadmsudodocker

When piping the output to a command that can parse newlines, this can be handy.

FAQs for id Command in Linux

Conclusion

If no username or ID is specified as an argument, the id command publishes information about the currently logged-in user.

If you have any queries, please leave a comment below and we’ll be happy to respond to them.