// learn · linux · rhcsa · 10 min

Local users and groups.

A user account isn't one thing — it's a few lines spread across /etc/passwd, /etc/shadow, and /etc/group, plus a home directory and a mail spool. Read each field, then learn the commands that create, modify, lock, and delete accounts.

// users and groups

A Linux account is a few lines of text plus a home directory. Once you can read /etc/passwd, /etc/shadow, and /etc/group, the management commands stop feeling magic.

// before you start

you should know

·Comfortable viewing files (cat, less) and basic permissions
·Know that root is the admin account
·Helpful: the file-permissions / chmod tool for the next lesson

by the end you'll

Read every field of a passwd/shadow/group line, and run the commands to create, modify, lock, and delete accounts safely.

pace: 10 minutes

account files — step 1 / 6 · /etc/passwd

/etc/passwd — seven colon-separated fields

Every account has one line in /etc/passwd with seven fields separated by colons: username, password placeholder (almost always 'x'), UID, primary GID, GECOS (a free-text comment, historically the user's full name), home directory, and login shell. This file is world-readable — that's fine, because the actual password hash lives elsewhere.

// key insight

The kernel only knows numbers — UIDs and GIDs. Usernames and group names are a convenience layer that /etc/passwd and /etc/group map to those numbers. That's why a file copied to another system can suddenly be "owned" by a different user: same UID, different name-to-number mapping.

// exam-ready · the account commands & files

$id aliceuid, gid, all groups at once

$getent passwd alicepasswd entry (works with LDAP too)

$useradd -m -s /bin/bash alicecreate + home + shell

$useradd -r svcsystem account (no aging, low UID)

$usermod -aG wheel aliceAPPEND to a group (don't drop -a)

$usermod -L / -U alicelock / unlock password

$userdel -r alicedelete + home + mail spool

$passwd aliceset/change password

$passwd -l / -u alicelock / unlock (like usermod -L/-U)

$chage -l alicelist aging info

$chage -M 90 -W 7 alice90-day max, 7-day warning

$groupadd developerscreate a group

$gpasswd -a alice developersadd member to a group

$newgrp developersswitch primary group for this shell

$/etc/skeltemplate copied into new home dirs

$/etc/login.defsdefault UID range, aging, etc.

// check yourself

4 quick questions

Where is a user's actual hashed password stored?

You run `usermod -G developers alice` to add alice to the developers group. What's the bug?

What's the difference between a primary and a supplementary group?

You want to disable password login for a departing employee but keep their files and audit trail. Best move?

These aren't graded — they're just for active recall, which is what actually makes the lesson stick.

👥

// next: what they can touch

chmod calculator

Now that you can create users and groups, decide what they can read and write. Flip permission bits and watch rwx ↔ octal update in lockstep.

open →

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keep going — these pair well with what you just learned.

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