2. Adding user accounts

Let's create a new user:
```
useradd --help
```
```
useradd -m -s /bin/bash test1
```
Only the superuser can create new accounts, so let's use sudo:
```
sudo useradd -m -s /bin/bash test1
```
The option -m tells it to create a home directory for the user, which is by default located at /home/, and the option -s tells it what shell to use for this user.
```
ls /home/
```
```
ls -al /home/test1/
```
Users normally cannot access the content of each other. Superuser can access everything.
```
sudo ls -al /home/test1/
```
We should also set a password for test1:
```
sudo passwd test1
```
Let's switch to this user and try some commands:
```
sudo su -l test1
```
su means: 'switch user'
```
pwd
```
```
whoami
```
```
id
```
When a user account is created, the system assigns it a number called user ID or uid, which is mapped to a username for the sake of humans. Each user is also assigned a primary group ID (or gid) and may belong to additional groups.
```
exit
```
Back to the first user.
```
pwd
whoami
id
```
User accounts are defined in /etc/passwd and groups in /etc/group. However the passwords of the users are stored in /etc/shadow:
```
ls -l /etc/passwd
```
```
file /etc/passwd
```
```
less /etc/passwd
```
You can see that besides the normal users there are also some system users, including the superuser (or root), with uid=0.
```
ls -l /etc/group
```
```
file /etc/group
```
```
less /etc/group
```
```
ls -l /etc/shadow
```
```
file /etc/shadow
```
```
less /etc/shadow
```
You don't have permission to see the content of this file.
```
sudo less /etc/shadow
```
The command chown can be used to change the owner and/or the group of a file. Let's try it:
```
chown root: foo.txt
```
```
whoami
```
Superuser privileges are required to use it. Let's try with sudo.
```
sudo chown root: foo.txt
```
```
ls -l foo.txt
```
```
chown test1:root foo.txt
```
```
ls -l foo.txt
```

Download lesson03/part2.cast

Loading asciinema cast...