# Managing users and groups

### I. Users :  <a href="#i.-commands" id="i.-commands"></a>

Most common <mark style="color:yellow;">$COMMANDS</mark> and <mark style="color:yellow;">FILES</mark> used to manage users. consult "<mark style="color:green;">man $command</mark> " for more informations.

#### **Commands :** <a href="#undefined" id="undefined"></a>

* useradd <mark style="color:red;">\<username></mark> -> to add new user.
* userdel <mark style="color:red;">\<username></mark> -> to delete an existed user.
* usermod <mark style="color:green;">-option</mark> <mark style="color:red;">\<username></mark> -> to modify a user characteristics.

**Files :&#x20;**&#x20;

* vim /etc/default/useradd -> <mark style="color:blue;">useradd default config file.</mark>
* vim /etc/passwd | vipw -> <mark style="color:blue;">verify the creation of your user with wanted properties.</mark>
* vim /etc/shadow -> <mark style="color:blue;">stores encrypted user passwords and is accessible only to the root user.</mark>

### II . Groups :

Most common <mark style="color:yellow;">$COMMANDS</mark> and <mark style="color:yellow;">FILES</mark> used to manage groups. consult "<mark style="color:green;">man $command</mark> " for more informations.

#### Commands :&#x20;

* groupadd <mark style="color:red;">\<groupname></mark> -> to create new group.
* groupdel <mark style="color:red;">\<groupname></mark> -> to delete an existing group.
* groupmod <mark style="color:red;">\<groupname></mark> -> modify a group definition on the system.
* lid <mark style="color:green;">-g</mark> <mark style="color:red;">\<groupname></mark> -> display the members of <mark style="color:red;">\<groupname></mark>.
* groupmems -g <mark style="color:red;">\<groupname></mark> -l -> administer members of a user's primary group
* other commands : groups | id | getent group ..

#### Files :

* vim /etc/group | vigr -> <mark style="color:blue;">to list groups in your system.</mark>
* vim /etc/gshadow -> <mark style="color:blue;">readable only by the root user and contains an encrypted password for each grou</mark>

### Configuration files :&#x20;

Let's start explaining the contents of /<mark style="color:green;">etc</mark>/<mark style="color:green;">passwd</mark> "<mark style="color:red;">vipw</mark>" file.

```
chxmxii:x:1000:1000:RHEL8VM:/home/chxmxii:/bin/bash
```

here we took an example of a user called <mark style="color:blue;">chxmxii</mark>. as you can see this line contains 7 fields separated by <mark style="color:green;">":",</mark> I will try to explain it for you one by one.

1. <mark style="color:red;">chxmxii :</mark> is the username.
2. <mark style="color:red;">x :</mark> is the password.
3. <mark style="color:red;">1000 :</mark> User ID.
4. <mark style="color:red;">1000 :</mark> Group ID.
5. <mark style="color:red;">RHEL8VM :</mark> Comment. "GECOS"
6. <mark style="color:red;">/home/chxmxii :</mark> Home Directory
7. <mark style="color:red;">/bin/bash :</mark> shell.

After understanding /<mark style="color:green;">etc</mark>/<mark style="color:green;">passwd</mark>, lets move on and find out what does /<mark style="color:green;">etc</mark>/<mark style="color:green;">shadow</mark> contains.&#x20;

```
chxmxii:$1$KfyGjDYU$OPkmq6g6pFehQk0DxUiZ80:18988:0:99999:7:::
```

Continuing with the same user <mark style="color:blue;">chxmxii</mark>,  unlike "vipw" /etc/shadow contains 9 fields which are :&#x20;

1. <mark style="color:red;">chxmxii :</mark> username
2. <mark style="color:red;">$1$KfyGjDYU$OPkmq6g6pFehQk0DxUiZ80 :</mark> encrypted password using the format *$type$salt$hashed* and eight to 12 characters long.
3. <mark style="color:red;">18988 :</mark> last password change since 1st January 1970.
4. <mark style="color:red;">0 :</mark> The minimum number of days that must elapse before the password can be changed by the user.
5. <mark style="color:red;">99999 :</mark> The number of days after which the password must be changed.
6. <mark style="color:red;">7 :</mark> Warning period.
7. <mark style="color:red;">? :</mark> Inactivity period ( since Jan. 1, 1970).
8. <mark style="color:red;">? :</mark> Expiration date (The date on which the account was disabled.).
9. <mark style="color:red;">? :</mark> This field is left empty and reserved for future use.

{% hint style="info" %}
Sometimes you will find "!" and "!!" within the password field.

"!" means the password is locked.

"!!" means the password is disabled.&#x20;
{% endhint %}

### Hints :&#x20;

* If you want to edit the password quality go to  <mark style="color:green;">"/etc/security/pwquality.conf"</mark> .
* If you want to edit the user configuration go to <mark style="color:green;">"/etc/default/useradd"</mark> .&#x20;
* If you want to edit the umask and pw\.age.. go to <mark style="color:green;">"/etc/login.defs"</mark> .

{% hint style="danger" %}
make sure to create a backup file before editing directly.

f.g : <mark style="color:yellow;">cp /etc/login.defs /etc/login.defs-original</mark>
{% endhint %}

* Created files under <mark style="color:blue;">**/etc/skel**</mark> will be created in <mark style="color:red;">**/home/$USER**</mark> upon creation.

### I . Practice Time:&#x20;

Create user chxmxii with the properties below :&#x20;

* UID : 1544 | GID : 1552 | GECOS : RHELV8 | HomeDir : /home/chxmxii | Shell : /bin/zsh
* make sure chxmxii is a member of wheel group.
* Make sure a file with name "Rules" is created in user home directory upon creation.

#### Answer :&#x20;

```
useradd -u 1544 -g 1552 -c "RHELV8" -d /home/chxmxii -s /bin/zsh chxmxii
usermod -aG wheel chxmxii
touch /etc/skel/Rules
```

{% hint style="success" %}
You have just finished learning users and group managing, lets pass to the next module <mark style="color:blue;">ownerships and permissions.</mark>
{% endhint %}