Create users and groups on Oracle Linux

Introduction

The following tutorial provides step-by-step procedures to perform user and group administration on Oracle Linux. You will create users and groups, implement user private groups, and grant user elevated privileges.

Objectives

In this lab, you'll:

Create a new user and explore user's home directory
Create a new group and add user to group
Utilize the user private group scheme and implement write access to a directory
Administer the sudo command for granting root privileges

What Do You Need?

A system with Oracle Linux installed

Note: When using the free lab environment, see Oracle Linux Lab Basics for connection and other usage instructions.

Administer User Accounts

In this section, you use command-line utilities to create a new user account, view files that are updated when adding a new user, modify a user account, set a password for the new user, and log in as the new user.

Open a terminal and connect to your Oracle Linux instance.
Become the root user.
```
sudo su -
```
As the root user, add a user named alice.
```
useradd alice
```
The user is added to the /etc/passwd file.
View the alice entry in the /etc/passwd file.
```
grep alice /etc/passwd
```
The output shows:
- The new user’s UID and GID are the same (1001).
- A home directory was created for the new user (/home/alice).
- The default shell for the new user is /bin/bash.
View the home directories.
```
ls -l /home
```
In this example, the opc user already existed.
A home directory was created for the new user because the CREATE_HOME parameter in /etc/login.defs is set to yes.
View the CREATE_HOME parameter in the /etc/login.defs file.
```
grep CREATE_HOME /etc/login.defs
```
View the default settings for a new user, stored in /etc/default/useradd.
```
cat /etc/default/useradd
```
The SKEL parameter is set to /etc/skel.
View the contents of the /etc/skel directory.
```
ls -la /etc/skel
```
View the contents of the alice home directory.
```
ls -la /home/alice
```
The contents of SKEL (/etc/skel) are copied to the new user’s home directory.
View the new alice entry in the /etc/group file.
```
grep alice /etc/group
```
Because Oracle Linux uses a user private group (UPG) scheme, a new private group (alice, GID=1001) was created when the alice user was created.
Modify GECOS information for the alice user. View the alice entry in the /etc/passwd file before and after modifying GECOS information.
```
grep alice /etc/passwd
usermod -c "Alice Smith" alice
grep alice /etc/passwd
```
Create a password of AB*gh246 for the alice user. View the alice entry in the /etc/shadow file before and after creating a password for alice.
```
grep alice /etc/shadow
passwd alice
grep alice /etc/shadow
```
The !! for alice is replaced with a hashed password value.
Exit the root login and login as the alice user. Provide the password of AB*gh246 when prompted.
```
exit
su - alice
```
Verify you are the alice user and your current directory is the alice user's home directory.
```
whoami
pwd
```
Exit the alice user's shell and become the root user.
```
exit
sudo su -
```
As the root user, add a user named oracle which is used later in this lab.
```
useradd oracle
```
Create a password of XY*gh579 for the oracle user.
```
passwd oracle
```

Administer Group Accounts

In this section, you create a new group account and add a user to this new group.

As the root user, add a group named staff.
```
groupadd staff
```
The group is added to the /etc/group file.
View the last 10 entries in the /etc/group file.
```
tail /etc/group
```
The GID (1003) for the new group is incremented by one.
Add the alice user to the staff group. View the staff group entry in the /etc/group file.
```
usermod -aG 1003 alice
grep staff /etc/group
```
The alice user has a secondary group membership in the staff group.
View the primary group membership for alice.
```
grep alice /etc/passwd
```
The alice user's primary group is still 1001.

Implement User Private Groups

In this section, you use the User Private Groups scheme to give different users write access to files in a single directory.

As the root user, create the /staff directory.
```
mkdir /staff
```
View the /staff directory and its permissions.
```
ls -ld /staff
```
Change group ownership for the /staff directory to the staff group. The -R option (recursive) sets the group for files and directories within /staff. View the /staff directory and its permissions after changing the group ownership.
```
chgrp -R staff /staff
ls -ld /staff
```
The owner of the /staff directory is still root, but the group is now staff.
Set the setgid bit on /staff directory. Then view the permissions on the /staff directory.
```
chmod -R 2775 /staff
ls -ld /staff
```
The group permissions on the /staff directory have changed.
Add the oracle user to the staff group. View the staff entry in the /etc/group file after adding the oracle user.
```
usermod -aG staff oracle
grep staff /etc/group
```
Both alice and oracle users have secondary group membership in the staff group.
Become the oracle user. You are not prompted for the oracle user's password because you currently are the root user. Verify you are the oracle user and your current directory is the oracle user's home directory.
```
su - oracle
whoami
pwd
```
Display group membership for the oracle user.
```
groups
```
The oracle user belongs to two groups - oracle and staff.
Change to the /staff directory. Create a new file in the /staff directory named oracle_file. Display the permissions and ownership of the new file.
```
cd /staff
touch oracle_file
ls -l oracle_file
```
The permissions are read/write for the staff group.
Become the alice user. Provide the password of AB*gh246 when prompted. Verify you are the alice user.
```
su - alice
whoami
```
Display group membership for the alice user.
```
groups
```
The alice user belongs to two groups - alice and staff.
Change to the /staff directory. Create a new file in the /staff directory named alice_file. Display the permissions and ownership of the new files.
```
cd /staff
touch alice_file
ls -l
```
The permissions are read/write on both files for the staff group.
As the alice user, use the touch command to update the time stamp on the oracle_file. View the files to verify the time has changed.
```
touch oracle_file
ls -l
```
Updating the time stamp implies write permissions on the file as the alice user, even though the file was created by the oracle user.
Exit both the alice user's shell, and the oracle user's shell, to return to the root user's shell. Verify that you are the root user.
```
exit
exit
whoami
```

Option 1: Grant Elevated Privileges to a User

In this section, you grant sudo privileges to a user by adding an entry to the /etc/sudoers file.

Become the alice user. You are not prompted for alice password because you currently are the root user. Verify you are the alice user.
```
su - alice
whoami
```
As the alice user, attempt to add newuser.
```
useradd newuser
```
The alice user does not have permission to add newuser.
Insert the sudo command before the previous useradd command to add newuser. Provide the password of AB*gh246 when prompted.
```
sudo useradd newuser
```
The attempt to issue this administrator command without proper authorization is reported in the /var/log/secure file.
Exit the alice user's shell to return to the root user's shell. View sudoers entries in the /var/log/secure file.
```
exit
grep sudoers /var/log/secure
```
The alice : user NOT in sudoers entry for the attempted use of the /sbin/useradd command is in the /var/log/secure file. Multiple entries are shown in the example. You might only have a single entry.
As the root user, edit the /etc/sudoers file by using the visudo command.
```
visudo
```
This command opens the /etc/sudoers file using the vim editor.
In the /etc/sudoers file, add the following line to grant the alice user permission to run the /sbin/useradd command.
```
alice   ALL=(ALL)       /sbin/useradd
```
The new entry is highlighted. Save your changes and exit the visudo command.
Become the alice user. Attempt to add newuser without the sudo command. Insert the sudo command and attempt to add newuser a second time. Provide the password of AB*gh246 when prompted.
```
su - alice
useradd newuser
sudo useradd newuser
```
Verify newuser was added.
```
grep newuser /etc/passwd
ls -l /home
```
The newuser now exists. With the alice entry in the /etc/sudoers file, the alice user has sudo privileges to run the /sbin/useradd command.
Exit the alice shell to return to the root shell. Use the visudo command and delete the alice entry from the /etc/sudoers file that you added earlier in this lab.
```
exit
visudo
```
The entry to delete is highlighted. Delete the entire line, or as in this example, insert the # character to comment out the line. Save your changes and exit the visudo command.
Verify the alice user can no longer add a new user. Become the alice user. Attempt to add anotheruser with the sudo command.
```
su - alice
sudo useradd anotheruser
```
The attempt to issue this administrator command without proper authorization is reported in the /var/log/secure file.
Exit the alice user's shell to return to the root user's shell.
```
exit
```

Option 2: Grant Elevated Privileges to a User

In this section, you grant sudo privileges by adding a user to the wheel group.

As the root user, view the wheel entry in the /etc/sudoers file.
```
grep wheel /etc/sudoers
```
The %wheel ALL=(ALL) ALL entry in the /etc/sudoers file allows any member of the wheel group to execute any command, when preceded by sudo.
Add the alice user to the wheel group. Confirm the alice user is in the wheel group.
```
usermod -aG wheel alice
grep wheel /etc/group
```
User alice has a secondary group membership in the wheel group.
Become the alice user. You are not prompted for alice password because you currently are the root user. Verify you are the alice user.
```
su - alice
whoami
```
As the alice user, add thirduser using the sudo useradd command. Provide the password of AB*gh246 if prompted.
```
sudo useradd thirduser
```
Verify thirduser was added. The ls command fails until you insert sudo and provide alice password. This confirms the alice user has sudo privileges.
```
grep thirduser /etc/passwd
ls -la /home/thirduser
sudo ls -la /home/thirduser
```