In the world of system administration, managing users and groups efficiently is crucial. This article presents a shell script that automates user and group management on Linux systems, making the process seamless and efficient. The script takes in a file which consists of users to be added to a machine and their corresponding groups

Below is a detailed explanation of the shell script:

#!/bin/bash

# Check if the correct number of arguments is passed
if [ "$#" -lt 1 ]; then
    echo "Usage: $0 <filename>"
    exit 1
fi

# The second argument is the filename
filename="$1"

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

# Function to trim leading and trailing whitespace
trim() {
    local var="$*"
    # Remove leading whitespace
    var="${var#"${var%%[![:space:]]*}"}"
    # Remove trailing whitespace
    var="${var%"${var##*[![:space:]]}"}"
    echo -n "$var"
}

# Define the file to check
user_mgt_file_path="/var/log/user_management.log"
user_mgt_dir_path=$(dirname "$user_mgt_file_path")

# Check if the directory exists
if [ ! -d "$user_mgt_dir_path" ]; then
  # Create the directory if it doesn't exist
  mkdir -p "$user_mgt_dir_path"
fi

# Check if the file exists
if [ ! -f "$user_mgt_file_path" ]; then
  # Create the file if it doesn't exist
  touch "$user_mgt_file_path"
  echo "File '$user_mgt_file_path' created."
fi

# Define the file to check
user_pass_file_path="/var/secure/user_passwords.csv"
user_pass_dir_path=$(dirname "$user_pass_file_path")

# Check if the directory exists
if [ ! -d "$user_pass_dir_path" ]; then
  # Create the directory if it doesn't exist
  mkdir -p "$user_pass_dir_path"
  echo "Directory $user_pass_dir_path created..." >> $user_mgt_file_path
fi

# Check if the file exists
if [ ! -f "$user_pass_file_path" ]; then
  # Create the file if it doesn't exist
  touch "$user_pass_file_path"
  echo "File $user_pass_file_path created..." >> $user_mgt_file_path
fi

# Loop through each line in the file
while IFS= read -r line; do
  # Process each line
  # echo "Processing: $line"

  # Define the username and password
  # Trim leading and trailing whitespace
  username=$(trim "${line%%;*}")
  password=$(LC_CTYPE=C < /dev/urandom tr -dc 'A-Za-z0-9!@#$%&*' | head -c 16)

  # Generate a random password
  echo "Password generated for user $username" >> $user_mgt_file_path


  usergroups=$(trim "${line#*;}")

  # Split the usergroups into an array
  IFS=',' read -r -a groups_array <<< "$usergroups"
  for i in "${!groups_array[@]}"; do
      groups_array[$i]=$(trim "${groups_array[$i]}")
      # groups_array[$i]=$(echo "${groups_array[$i]}" | xargs)
  done

  # Extract the primary group (first element)
  primary_group="${groups_array[0]}"

  # Extract the remaining groups
  if [ "${#groups_array[@]}" -gt 1 ]; then
      additional_groups=$(IFS=,; echo "${groups_array[*]:1}")
  else
      additional_groups=""
  fi

  # Function to check if a group exists, and create it if it doesn't
  create_group_if_not_exists() {
      groupname="$1"
      if ! getent group "$groupname" > /dev/null 2>&1; then
          groupadd "$groupname"
          echo "User group '$groupname' created..." >> $user_mgt_file_path
      else
          echo "User group '$groupname' already exist! Skipping" >> $user_mgt_file_path
      fi
  }

  # Check and create primary group
  create_group_if_not_exists "$primary_group"

  # Check and create additional groups
  for group in "${groups_array[@]}"; do
      create_group_if_not_exists "$group"
  done


  # Check if the group already exists
  if ! getent group "$username" > /dev/null 2>&1; then
    # Create the group if it doesn't exist
    groupadd "$username"
    echo "Directory $user_pass_dir_path created..." >> $user_mgt_file_path # TODO
  fi

  # Check if the user already exists
  if id "$username" &>/dev/null; then
    echo "User '$username' already exists. Skipping..."
    echo "User '$username' already exists. Skipping..." >> $user_mgt_file_path
  else
    # Create the user with the primary group and additional groups if any
    if [ -n "$additional_groups" ]; then
        useradd -m -g "$primary_group" -G "$additional_groups" -s /bin/bash "$username"
    else
        useradd -m -g "$primary_group" -s /bin/bash "$username"
    fi

    # Create the user with the specified group and set the password
    # useradd -m -g "$username" -s /bin/bash "$username"
    echo "$username:$password" | chpasswd
    echo "User '$username' created! Password has also been set for the user" >> $user_mgt_file_path

    # Display the created username and password
    echo "Password for user '$username' is: $password" >> $user_pass_file_path

    # Set the home directory path
    home_directory="/home/$username"

    # Set permissions and ownership for the home directory
    chown "$username:$primary_group" "$home_directory"
    chmod 755 "$home_directory"

    # Ensure appropriate permissions for additional groups
    for group in "${groups_array[@]}"; do
        if [ "$group" != "$primary_group" ]; then
            chmod g+rx "$home_directory"
            setfacl -m "g:$group:rx" "$home_directory"
        fi
    done

    echo "User $username created with home directory $home_directory" >> $user_mgt_file_path
    echo "Users created!"
  fi
done < "$filename"

How the Script Works

1. Argument Check: The script starts by checking if the correct number of arguments is passed. It expects a filename as an argument.
2. File Existence Check: It then checks if the provided file exists.
3. Whitespace Trimming Function: A function trim is defined to remove leading and trailing whitespaces from strings.
4. Log and Password File Management: The script ensures that the directories and files for logging user management actions and storing user passwords exist.
5. Processing the Input File: The script reads the input file line by line, extracting the username and user groups, generating random passwords, and managing user and group creation accordingly.

Using the Script

To use the script, save it to a file, for example, user_mgmt.sh, and make it executable:

chmod +x user_mgmt.sh

Run the script with the input file containing user information:

./user_mgmt.sh users.txt

OR

bash user_mgmt.sh users.txt

Learn More About the HNG Internship

• https://hng.tech/internship
• https://hng.tech/hire

This script automates a significant part of user and group management, ensuring consistency and saving time for system administrators. The HNG Internship program encourages such practical projects, enhancing the skills of interns through real-world tasks. If you’re interested in joining or hiring from the HNG Internship, visit the links above.

Feel free to ask if you have any questions or need further modifications!