Creating Bash Scripts for User Management

Introduction

A Bash script is a file containing a sequence of commands that are executed on a Bash shell. It allows performing a series of actions or automating tasks. This article will examine how to use a Bash script to create users dynamically by reading a CSV file. A CSV (Comma Separated Values) file contains data separated by commas or other delimiters.

In Linux systems, multiple users can access the same machine, necessitating the creation of various users with access to the machine. This article demonstrates a Bash script for creating users from a CSV file, assigning them to groups, and generating random passwords.

Objective

The main purpose of this article is to show how to create users in a Linux system using a simple bash script.

Bash Script Overview

We will follow a sequence of steps to create the Bash script. You can clone the full code from this GitHub repository.

Reading the CSV File

The first step is to read the CSV file. The Bash script will take the CSV file as an input argument. The script will throw an error and exit if no input is provided. Below is the code snippet for checking the file:

CSV_FILE="$1"

# Check if the file exists
if [[ ! -f "$CSV_FILE" ]]; then
    echo "File not found!"
    exit 1
fi

Creating a Directory and File to Store Users

After reading the file, we need to create a directory and file to store the usernames and passwords of any new users created which will be accessible only to the file owner. To avoid creating a directory that already exists, we first check for its existence before creating a new one:

PASSWD_DIR="/var/secure"
PASSWD_FILE="user_passwords.csv"

if [ ! -d "$PASSWD_DIR" ]; then
    mkdir -p "$PASSWD_DIR"
    touch "$PASSWD_DIR/$PASSWD_FILE"
    chmod 600 "$PASSWD_DIR/$PASSWD_FILE"
fi

Reading the Usernames and Group Names

After checking the text file and creating the file for storing the users, we will iterate through the rows to create users and assign them to groups. While creating the users, a random password is generated for each user. The code snippet below shows how users are created:

LOG_PATH="/var/secure/user_management.txt"

# Split the user and group by ";"
while IFS=';' read -r user groups; do
    user=$(echo $user | tr -d ' ')
    groups=$(echo $groups | tr -d ' ')

    # Check if the user exists
    if id "$user" &>/dev/null; then
        echo "$(date "+%Y-%m-%d %H:%M:%S") user $user already exists." >> "$LOG_PATH"
    else
        # Generate random password
        echo "$(date "+%Y-%m-%d %H:%M:%S") user with username $user already exist." >> $logPath

        # Create user and assign password
        useradd -m "$user"
        echo "$user:$password" | chpasswd

        # Store the created user and password
        echo "$user,$password" >> "$PASSWD_DIR/$PASSWD_FILE"
        echo "$(date "+%Y-%m-%d %H:%M:%S") user with username: $user cretaed by user $(whoami)" >> $logPath
    fi

    # Split the groups by comma and add user to each group
    IFS=',' read -ra GROUP_ARRAY <<< "$groups"
    for group in "${GROUP_ARRAY[@]}"; do
        # check for the existense of group before creating group
         if [ $(getent group $group) ]; then
            echo "$(date "+%Y-%m-%d %H:%M:%S") group: $group already exists." >> $logPath
         else
            groupadd $group
            echo "$(date "+%Y-%m-%d %H:%M:%S") group: $group created by user $(whoami)."  >> $logPath
        fi

        # check for the existense of user in a group before addding the user
        if getent group "$group" | grep -qw "$user"; then
            echo "$(date "+%Y-%m-%d %H:%M:%S") user: $user is already in group: $group"  >> $logPath
        else
            adduser $user $group
            echo "$(date "+%Y-%m-%d %H:%M:%S") user with username: $user was added to group :$group by user $(whoami)" >> $logPath
        fi


done < "$CSV_FILE"

Important Notes

1. Separators: The CSV file uses ; to separate usernames and groups, and , to separate multiple groups.
2. Logging: All actions taken concerning user creation are logged to a file with timestamps.

Running the Script

To run the script, follow these steps:

1. Ensure you are running on a Linux system with root privileges or use the sudo command.
2. Clone the repository and navigate to the directory.

3. Create a sample CSV file users.csv as shown below.
   

   mary; developer,sys-admin
   paul; sys-admin
   peter; operations
   

4. Execute the script as shown add sudo if you are not a root user:
   

   bash create_users.sh users.csv
   

After running the script, new users will be created, and their details will be stored in /var/secure/user_passwords.csv. All actions will be logged in /var/secure/user_management.txt.

Summary

The steps outlined in this article are not exhaustive other sources of information such as documentation can be used to complement your article.
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