Users and Groups

axeberg implements Linux-like multi-user support with file-based persistence.

User Database

Users are stored in /etc/passwd with standard format:

root:x:0:0::root:/bin/sh
user:x:1000:1000::/home/user:/bin/sh
nobody:x:65534:65534::/nonexistent:/bin/sh

Format: name:x:uid:gid:gecos:home:shell

Password Storage

Passwords are stored in /etc/shadow:

root:0000573001aaef2b:19000:0:99999:7:::
user:!:19000:0:99999:7:::

• ! or * means no password (login allowed)
• Hash is a simple hash for demo purposes

Groups

Groups are stored in /etc/group:

root:x:0:
wheel:x:10:user
user:x:1000:

Format: name:x:gid:member1,member2,...

Default Users

Default Groups

User Management Commands

login

$ login alice password
Login successful: alice
  PID: 5, SID: 5, PGID: 5
  UID: 1001, GID: 1001

Creates a new session as the specified user.

logout

$ logout
Session 5 ended for user 'alice'

Ends the current session.

su

$ su              # Switch to root (requires password)
$ su alice        # Switch to alice
$ su - alice      # Login shell (sets HOME, etc.)

sudo

$ sudo whoami     # Run as root
$ sudo -u bob cmd # Run as bob

Requires membership in wheel group.

useradd

$ useradd alice           # Create user with new group
$ useradd -g users bob    # Create with existing group

groupadd

$ groupadd developers

passwd

$ passwd secret           # Set own password
$ passwd alice newpass    # Set alice's password (root only)
$ passwd alice            # Clear password (root only)

id

$ id
uid=1000(user) gid=1000(user) groups=1000(user),10(wheel)

whoami

$ whoami
user

who / w

$ who
USER     TTY        LOGIN@
user     tty1       12:34

Permission Model

File permissions follow Unix conventions:

-rwxr-xr-x  1 root   root    4096 Jan  1 00:00 /bin/ls
drwxr-xr-x  2 alice  users   4096 Jan  1 00:00 /home/alice

Permission Bits

Categories

1. Owner (u): Matches file's uid
2. Group (g): Matches file's gid or supplementary groups
3. Other (o): Everyone else

Root Bypass

UID 0 (root) bypasses all permission checks.

Kernel API

UserDb Structure

pub struct UserDb {
    users: HashMap<Uid, User>,
    groups: HashMap<Gid, Group>,
}

pub struct User {
    pub name: String,
    pub uid: Uid,
    pub gid: Gid,
    pub home: String,
    pub shell: String,
    pub password_hash: Option<String>,
}

Persistence Functions

// Save to /etc/passwd, /etc/shadow, /etc/group
kernel.save_user_db();

// Load from files
kernel.load_user_db();

Syscalls

Related Documentation

• Process Model - Process credentials
• Syscall Interface - User syscalls
• Shell - User commands