Understand identities and sessions

By the end: Identify the effective user, current sessions, and where elevated access comes from.

The idea

A process runs with an identity and group memberships. That identity may differ from the person who originally logged in. Observe first; do not switch accounts or change a password on a shared machine merely to complete a lesson. Session tools depend on the distribution and whether login accounting is enabled.

Your command toolkit

whoami

What it solves: Identify the effective user.

whoami

Reports the user associated with the current effective UID. After an authorized identity change, it may differ from the original login user.

who

What it solves: Inspect recorded login sessions.

who

Reads login accounting information. Containers and some modern sessions may not appear in this traditional record.

w

What it solves: See logged-in sessions and activity.

w

Combines session details with uptime and load information. It is a different command from finger.

groups

What it solves: Inspect current group memberships.

groups

Groups contribute to permission checks. A membership change may require a new login session to take effect.

finger

What it solves: Read account information where supported.

finger "$(whoami)"

An optional, older tool. Limit practice to your own local account; remote finger services may be absent and can expose personal information.

last

What it solves: Review recorded login history.

last -n 5

Reads historical login accounting, if available. Missing records do not prove that no one logged in.

login

What it solves: Understand how a login session starts.

man login

Study the installed implementation. Running login can replace or change a session, so this course uses its manual rather than opening another account.

passwd

What it solves: Inspect password status without changing it.

passwd -S

On common shadow-utils systems, -S reports your own account's password status. Running passwd without that option starts a password change.

su

What it solves: Understand switching to another identity.

su --help

su starts a shell or command as another user, subject to authentication. A login shell changes more environment settings than a simple user switch.

sudo

What it solves: Inspect how authorized elevation works.

sudo -l

Lists commands your policy permits and may ask for authentication. sudo is an authorization boundary, not a general fix for any error.

Before you move on

Try the guided lab below. Compare the result with the explanation, then record your reasoning in the workbook. A missing optional program or a restricted environment is something to explain, not a reason to change system settings blindly.