id command in Linux with examples

The 'id' command in Linux is a powerful tool used to display user and group names along with their numeric IDs (User ID - UID or Group ID - GID) of the current user or any specified user on the system. This command is particularly useful for system administrators and users who need to verify user identities and associated permissions.

What does the 'id' Command Do?

This command is useful to find out the following information as listed below:

• User name and real user id.
• Find out the specific User UID.
• Show the UID and all groups associated with a user.
• List out all the groups a user belongs to.
• Display the security context of the current user.

Syntax:

id [OPTION]… [USER]

Options:

• '-g': Prints only the effective group ID of the user.
• '-G': Prints all group IDs associated with the user.
• '-n': Displays names instead of numeric IDs.
• '-r': Shows the real ID instead of the effective one.
• '-u': Prints only the effective user ID.
• '--help': Displays help messages for the id command and exits.
• '-version': Shows the version information and exits.

Note: Without any OPTION it prints every set of identified information i.e. numeric IDs.

'id' command Examples in Linux

Let us look at some of the examples of 'id' command in Linux to better understand the concept.

1. To print your own 'id' without any Options

To display your own user and group IDs, simply run:

id

The output shows the ID of current user UID and GID.

2. To find a specific users 'id'

Now assume that we have a user named master, to find his UID we will use the command:

id -u master

This will display only the UID of the specified user.

3. To find a specific users GID

Again assuming to find GID of master, we will use the command:

id -g master

This option will show the effective group ID of the user.

4. To find out UID and all groups associated with a username

In this case we will use the user "master" to find UID and all groups associated with it, use command:

id master

5. To find out all the groups a user belongs to

Displaying the UID and all groups a user "master" belongs to:

id -G master                                                

6. To display a name instead of numbers

By default the 'id' command shows us the UDI and GID in numbers which a user may not understand, with use of '-n' option with '-u', '-g' and '-G'. Use command(s):

id -ng master 
or
id -nu master
or
id -nG master

7. To display real id instead of effective id

To show the real id with the use of '-r' option with '-g', '-u' and '-G, use command(s):

id -r -g master
id -r -u master
id -r -G master

Conclusion

By mastering the 'id' command and understanding its various options, you can enhance your ability to manage and troubleshoot user permissions on Linux systems. This command is a key tool in your Linux toolkit if you’re a system administrator or even a casual user.