id

Updated

September 4, 2026

Overview

id prints the real and effective user and group IDs for a process (by default, yours), plus supplementary groups. It is the authoritative quick identity tool for permissions debugging — better than whoami alone when groups and numeric IDs matter.

Syntax

id [options] [user]

Common Options

Option	Description
`-u`, `--user`	Print only user ID
`-g`, `--group`	Print only primary group ID
`-G`, `--groups`	Print all group IDs
`-n`, `--name`	Print names instead of numbers (with `-u`/`-g`/`-G`)
`-r`, `--real`	Real ID instead of effective
`-z`, `--zero`	NUL-terminate (with `-G` etc.)
`-A`	Security context extras on some systems
`-Z`	SELinux context (when available)

Examples with Explanations

Default

id
# uid=1000(alice) gid=1000(alice) groups=1000(alice),27(sudo),100(users)

Specific fields

id -u
id -un
id -g
id -gn
id -G
id -Gn

Other users

id www-data
id -un root
getent passwd www-data

Root check in scripts

if [ "$(id -u)" -ne 0 ]; then
  echo "need root" >&2
  exit 1
fi

Real vs effective (setuid context)

id -u
id -ru
id -u -r
# if they differ, effective privileges differ from real user

SELinux

id -Z

Format for logs

printf 'User: %s (UID: %d)\n' "$(id -un)" "$(id -u)"
echo "groups=$(id -Gn)"

Permission debugging pattern

id
namei -l /path/to/resource
ls -l /path/to/resource
getfacl /path/to/resource 2>/dev/null

Notes / Pitfalls

Names come from NSS (passwd/group/sssd/ldap) — offline LDAP can make lookups hang.
Prefer numeric IDs in scripts for comparisons; names can rename.
Supplementary groups affect file access; primary gid alone is incomplete.
Containers may show only a subset of host groups or remapped UIDs.
id user looks up that account; default is the calling process credentials.

2026-relevant notes

Systemd user sessions and linger affect available groups for some services — debug with id inside the unit’s environment (systemd-run --user).
Rootless containers: high UIDs on the host map to low UIDs inside.
For policy (“must be in group docker”), check id -nG | tr ' ' '\n' | grep -x docker.

Additional Resources

man id