Introduction
In this lab, we will explore the Linux id command, which is a useful utility for displaying information about the current user or any other user on the system. We will understand the purpose and usage of the id command, learn how to identify user and group information, and explore additional options and customizations.
The id command allows you to display the user ID (UID), group ID (GID), and the supplementary groups that a user belongs to. You can use it to get information about the current user or any other user on the system. Additionally, the id command can be used to display the effective user ID and group ID, which are the IDs used for permission checks when executing a command.
Understand the Purpose and Usage of the id Command
In this step, we will explore the purpose and usage of the id command in Linux. The id command is a useful utility that allows you to display information about the current user or any other user on the system.
The basic usage of the id command is as follows:
$ id
uid=1000(labex) gid=1000(labex) groups=1000(labex),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
This command displays the user ID (UID), group ID (GID), and the supplementary groups that the current user belongs to.
You can also use the id command to display information about another user by specifying the username as an argument:
$ id alice
uid=1001(alice) gid=1001(alice) groups=1001(alice),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
This will show the user and group information for the user alice.
The id command can also be used to display the effective user ID and group ID, which are the IDs used for permission checks when executing a command. You can use the -e option to display the effective IDs:
$ id -e
uid=1000(labex) gid=1000(labex)
Example output:
uid=1000(labex) gid=1000(labex) groups=1000(labex),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
Identify the User and Group Information Using the id Command
In this step, we will learn how to use the id command to identify the user and group information for the current user and other users on the system.
First, let's verify the user and group information for the current user:
$ id
uid=1000(labex) gid=1000(labex) groups=1000(labex),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
This output shows the user ID (UID), group ID (GID), and the supplementary groups that the current user labex belongs to.
You can also use the id command to display information about other users on the system. For example, to get the user and group information for the user alice, you can run:
$ id alice
uid=1001(alice) gid=1001(alice) groups=1001(alice),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
This command will display the UID, GID, and supplementary groups for the user alice.
Additionally, you can use the -u option to display only the user ID, and the -g option to display only the group ID:
$ id -u
1000
$ id -g
1000
Example output:
uid=1000(labex) gid=1000(labex) groups=1000(labex),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lxd),128(sambashare)
Explore Additional Options and Customizations of the id Command
In this final step, we will explore some additional options and customizations available with the id command.
One useful option is the -n flag, which displays the name instead of the numeric ID. For example:
$ id -nu
labex
$ id -ng
labex
This will show the username and group name instead of the numeric IDs.
You can also use the --help option to see all the available options for the id command:
$ id --help
Usage: id [OPTION]... [USER]
Print user and group information for the specified USER,
or (when USER omitted) for the current user.
-a print all information in a readable format
-Z, --context print only the security context of the process
-g, --group print only the effective group ID
-G, --groups print all group IDs
-n, --name print a name instead of a number, for -ugG
-r, --real print the real ID instead of the effective ID, with -ugG
-u, --user print only the effective user ID
-z, --zero delimit entries with NUL character, not whitespace;
not permitted in default format
--help display this help and exit
--version output version information and exit
Examples:
id
id username
id -a
id -u
id -g
This shows all the available options you can use with the id command to customize the output.
Finally, you can combine multiple options to get the desired information. For example, to get the username and group name for the current user:
$ id -un
labex
$ id -gn
labex
Example output:
$ id -un
labex
$ id -gn
labex
Summary
In this lab, you learned how to use the id command in Linux to display information about the current user or any other user on the system. The id command can show the user ID (UID), group ID (GID), and the supplementary groups that the user belongs to. You also explored how to use the -e option to display the effective user ID and group ID, which are the IDs used for permission checks when executing a command. Additionally, you learned how to use the id command to identify the user and group information for other users on the system by specifying their usernames as arguments.
