id command examples in linux ?

How do I find out the user and group’s names and numeric IDs of the current user or any users on

my server? How can I display and effective IDs on the system using command line options? In Linux,

how do I find a user’s UID or GID?

To find a user’s UID (user ID) or GID (group ID) and other information in Linux/Unix-like operating
systems, use the id command.

This command is useful to find out the following information:

• Get User name and real user ID
• Find a specific user’s UID
• List out all the groups a user belongs to
• Show the UID and all groups associated with a user
• Display security context of the current user
• Effective Linux or Unix user name and effective user ID (UID)
• Name of effective Linux or Unix user’s group and effective group ID (GID)

Purpose

Displays the system identifications of a specified user.

id command syntax

The basic syntax is:

id

id [UserNameHere]

id [options]

id [options] [UserNameHere]

 id --help

Usage: id [OPTION]... [USERNAME]

Print user and group information for the specified USERNAME,

or (when USERNAME omitted) for the current user.

  -a              ignore, for compatibility with other versions

  -Z, --context   print only the security context of the current user

  -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

      --help     display this help and exit

      --version  output version information and exit

Display your own UID and GID

Type the command:

id

Sample outputs:

id

uid=1000(dev) gid=1000(dev) groups=1000(dev),4(adm),24(cdrom),27(sudo)

How do I find a specific user’s UID?

In this example, find a dev user’s UID, type:

id -u {UserNameHere}

id -u dev

Sample output:

id -u dev

1000

How do I find a specific user’s GID?

In this example, find a dev user’s GID, run:

id -g {UserNameHere}

id -g dev

Sample output:

id -g dev

1000

How do I see the UID and all groups associated with a user name?

In this example, find the UID and all groups associated with a user called ‘root’, enter:

id {UserNameHere}

id root

Sample output:

id root

uid=0(root) gid=0(root) groups=0(root)

Find out all the groups a user belongs to  !!

In this example, display the UID and all groups associated (secondary groups) with a user called ‘dev’, run:

id -G {UserNameHere}

id -G dev

Sample output:

id -G dev

1000 4 24 27 30 46 108 124 142

How do I display real ID instead of the effective ID for specified user?

You can show the real ID for the -g, -G and -u options instead of the effective ID by passing the -r option:

id -r -g {UserNameHere}

id -r -u {UserNameHere}

### [NOTE]  -r and -G only works on Linux

id -r -G {UserNameHere}

id -r -u dev

Sample output:

id -r -u dev

1000

Determining root privileges in a script

Linux and Unix sysadmin relates shell scripts must be run by root user. The following shell script

shows how to determining root privileges in a script:

#!/bin/bash

## if root user not running this script, die with a message on screen ##

if [ $(id -u -r) -ne 0 ]

then

        echo "Requires root privileges. Please re-run using sudo."

        exit 1

fi