Introduction

This article explains a bash script (GitHub Repo) designed to automate Linux user account creation from a text file containing the said users, as well as a list of supplementary group(s). The script should create users and groups as specified in the prerequisites section, set up home directories with appropriate permissions and ownership, generate random passwords for the users, and log all actions in a file. In addition, the script should store the generated passwords securely in a text file.

Prerequisites

Before proceeding with this article, it’s pertinent that you have some basic knowledge of Linux OS and its commands. Although I have added clear comments to the script, a basic knowledge of Bash scripting is still required to follow along.

To run or use the script, take note of the following:

• Ensure you have sudo privileges as user and group management typically requires root access i.e. run the script with sudo or as root.
• The script is written for an Ubuntu distro but would still work for other Linux flavors.
• Each line in the text file to be passed to the script as an argument must be formatted as user; list of groups separated by commas. Sample file structure:

light; sudo,dev,www-data
idimma; sudo
mayowa; dev,www-data

Script Explanation

With the housekeeping out of the way, below is the breakdown of the script.

Validation of Input File

The script starts by checking that an input file is passed as an argument to the script and the path of the said file is valid (the file exists).
For both checks, I used the if conditional in combination with the logical AND operator ‘&&’, which only evaluates the second statement if and only if the first statement is true. If the first statement evaluates to true, the script exits immediately i.e. exit 1.

Helper Functions

Two helper functions are defined for random password generation and logging. The random password generator function – password_gen() uses the bash built-in $RANDOM variable which by default, generates random integer. The $RANDOM variable is piped to the base64 module to generate an alphanumeric password.

The logging function – logger() when called with an argument, would echo the current date and time together with the action to a file declared as $LOG_FILE.

Secure the Password File

The directory /var/secure is created if it does not exist and only the user has permissions on the directory.

Working with the Input File

The input file is first read line by line ($lines) and each line ($line – delimited by a newline character) is iterated over in a for loop.

The $line is then split to an array at the delimiter ‘;’ with a trailing whitespace (‘; ’). Remember that each line of the input file is formatted as so - user; list of groups. The first slice (string before the field separator/delimiter ‘; ’) is assigned to the $username variable and the other slice to the $groups variable.

User Creation

The script then checks if a user with the $username already exists and if true, skips to the next iteration. Otherwise, the helper password_gen() function is called and the value assigned to a $password variable. The useradd utility is then called with the following flags m, U and G (see the useradd man pages) to create the user.


For the user password, we use chpasswd utility to set the password with the $password generated. In addition, the password is then redirected to the $PASSWORD_FILE and appropriate permissions set on the file (only the user has permissions - rw).

Securing the User Home Directory

Finally, appropriate permissions are set on the user’s home directory so that only the user has read,write and execute permissions on the directory.

Running the Script

• Make the script executable: chmod +x /path/to/script. You might have to run this command as sudo
• Run the script with the input file as an argument: sudo ./path/to/script /path/to/inputfile.txt.
• You can verify the script ran successfully by running the following:

# View the $LOG_FILE
sudo cat /var/log/user_management.log
# View the $PASSWORD_FILE
sudo cat /var/secure/user_passwords.txt
# View the system accounts file
sudo cat /etc/passwd

Conclusion

As a Sysops/DevOps engineer, automation of user account management using bash scripts can significantly enhance efficiency and accuracy. Take note that the desired result can be achieved using a different logic and structure. For a more streamlined solution, refactoring the main part of the script into smaller functions should be considered.
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