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Linux System User Management Using A Bash Script

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Chimsom Okoro
·

4 min read

Introduction

HNG internship is a fast-paced remote bootcamp for learning and applying digital skills to to solve problems. One of the handful of problems that interns have been tasked to solve in the Devops track of cohort 11 is a Linux based user management system using a Bash script. A user is an entity in a Linux operating system, that can manipulate files and perform many other operations depending on their permissions. It is crucial to manage users and the kinds of access that they posses in a Linux System.

Objectives

In this article I will explain the create_user.sh script which is a script that manages users and groups and is majorly focused on doing the following:

  • Read a text file containing a list of users and their groups, where each line is formatted as user;groups

  • Set up home directories with appropriate permissions

  • Set up users and groups

  • Generate random passwords for Users

  • Save passwords in a protected file

  • Log all activities in a log file

  • Handle errors appropriately

Prerequisite

A Basic understanding of Bash Scripting and Linux users and groups

Script Breakdown

Step 1: Ensure Script runs as a bash script

#!/bin/bash

Step 2: Specify paths to Password and Log files

LOG_MANAGER_FILE="/var/log/user_management.log"
PASSWORD_FILE="/var/secure/user_password.txt"

Step 3: Create a function that generates a 16 character random password

generate_password() {
    openssl  rand -base64 16
}

Step 4: Create a function that logs activities with timestamp to the log file

log_message() {
    echo "$(date +'%Y-%M-%D-%S') -$1" >> "$LOG_MANAGER_FILE"
}

Step 5: Ensure that the text file to read is provided

if [ "$#" -eq 0 ]; then
 log_message "Error: user file not found. Please pass the user file as base argument "
 exit 1
fi

Step 6: Use root privileges to create the log file

if [ ! -f "$LOG_MANAGER_FILE" ]; then
 sudo touch "$LOG_MANAGER_FILE"
 log_message "created log management file at"
fi

Step 7: Create the secure directory and the password file with root privilege

if [ ! -f "$PASSWORD_FILE" ]; then
 echo "creating secure password directory..."
 sudo mkdir -p /var/secure
 sudo chmod 700 /var/secure
 sudo touch "$PASSWORD_FILE"
 sudo chmod go-rwx "$PASSWORD_FILE"
 log_message "created Password file "
fi

Step 8: While username and group is separated by Internal Field Separator(IFS);

  • Eliminate white spaces

  • Create a group with the same name as the username

  • Check if user already exists

  • Add user to the home directory => /home/user

  • Add the group to /etc/group

  • Generate a password and attach it to a user

while IFS=";" read -r username groups; do
 # Eliminate white spaces
 username=$(echo "$username" | xargs)
 groups=$(echo "$groups" | xargs)

 #create group with username as group name
 groupadd "$username"  &>> "$LOG_MANAGER_FILE"
 log_message "created user group"

 #check if user already exists
 if id -u "$username" &> /dev/null; then
  log_message "user already exists"
  continue
 fi

 #add user in the /home directory
 useradd -m -g  "$username" "$username" &>> "$LOG_MANAGER_FILE"
 log_message "user created in home directory"

 #add group in the etc/group directory
 for group in $(echo "$groups" | tr ',' ' '); do
    if ! grep -q  "^$groups:" /etc/group; then
     groupadd "$group" &>> "$LOG_MANAGER_FILE"
     log_message "created group: $group"
    fi
    #add user to the created group
   usermod -aG  "$group" "$username"
   log_message  "Added user: $username to: $group"
 done

 #assign passwords to users
 password=$(generate_password)
 echo "$username, $password" >> "$PASSWORD_FILE"
 echo "$password" | passwd --stdin "$username" &>> "$LOG_MANAGER_FILE"
 log_message "User Password generated and set for: $username"

done < "$1"

Conclusion

In this article we have explored writing a script that manages users and groups in a Linux system. The create_user.sh script automated the user provisioning based on a user list file. It traversed a text file that contains a list of users and their groups, ensured that users are created and added to the right groups and also handled errors in the case of pre-existence with every step properly documented in a log file.

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