id Command in Linux: Display User and Group Information

The id command prints user and group identity for any account on the system. It shows the real user ID, primary group ID, and all supplemental group memberships — the quickest way to confirm what permissions an account holds.

How to Use the id Command in Linux

The syntax is:

bashid [OPTIONS] [USERNAME]

Run without arguments to see the current user:

bashid

Output: uid=1000(linuxize) gid=1000(linuxize) groups=1000(linuxize),4(adm),27(sudo),998(docker)

Each field shows the numeric ID followed by the name in parentheses. uid = real user ID; gid = real primary group ID; groups = primary group plus all supplemental groups. Effective IDs appear in the output only when they differ from the real ones.

If SELinux is enabled, a context= field is appended automatically.

Query another user by name or UID:

bashid markid 1001

Name lookup takes precedence over numeric lookup. If a user named 1010 exists alongside a user with UID 1010, id 1010 returns the user whose name is 1010. Prefix with + to force numeric UID lookup:

bashid +1010

id Command Options and Field Modifiers

These options extract a single field — especially useful in scripts where you need one value rather than the full output:

-n and -r are modifiers — they do not work alone. You must combine them with -u, -g, or -G:

bashid -un    # effective username (same output as whoami)id -Gn    # all group names (same output as the groups command)id -ur    # real user ID as a number

Real vs effective IDs. The real user ID is the account that started the process. The effective user ID is what the kernel checks for permission decisions. They are usually identical. They diverge when a setuid binary runs — for example, passwd temporarily elevates privileges to write to /etc/shadow.

The -Z option prints the SELinux security context. If SELinux is not enabled, id returns: id: --context (-Z) works only on an SELinux-enabled kernel.

Using id in Shell Scripts

Check if running as root:

bashif [ "$(id -u)" -eq 0 ]; then  echo "Running as root"else  echo "Root privileges required"  exit 1fi

Comparing to 0 is more reliable than checking for the string “root” — UID 0 is always root, regardless of how the account is named.

Check group membership:

bashif id -Gn | grep -qw docker; then  echo "User is in the docker group"fi

-q makes grep exit silently with a status code. -w enforces a whole-word match, so a group named “sudocker” does not trigger a match for “docker”.

Store the current username for logging:

bashCURRENT_USER="$(id -un)"echo "Script started by $CURRENT_USER"

Use id to confirm your current identity, id -Gn to check group memberships, and id -u in scripts to test for root. Leave a comment below if you run into any issues.