Advanced Linux Shell Scripting for DevOps Engineers with User Management
Rajat Chauhan is a skilled Devops Engineer, having experience in automating, configuring, deploying releasing and monitoring the applications on cloud environment.
• Good experience in areas of DevOps, CI/CD Pipeline, Build and Release management, Hashicorp Terraform, Containerization, AWS, and Linux/Unix Administration. • As a DevOps Engineer, my objective is to strengthen the company’s applications and system features, configure servers and maintain networks to reinforce the company’s technical performance. • Ensure that environment is performing at its optimum level, manage system backups and provide infrastructure support. • Experience working on various DevOps technologies/ tools like GIT, GitHub Actions, Gitlab, Terraform, Ansible, Docker, Kubernetes, Helm, Jenkins, Prometheus and Grafana, and AWS EKS, DevOps, Jenkins. • Positive attitude, strong work ethic, and ability to work in a highly collaborative team environment. • Self-starter, Fast learner, and a Team player with strong interpersonal skills • Developed shell scripts (Bash) for automating day-to-day maintenance tasks on top of that have good python scripting skills. • Proficient in communication and project management with good experience in resolving issues.
Task 1: Create Directories Using Shell Script:
Write a bash script
createDirectories.shthat, when executed with three arguments (directory name, start number of directories, and end number of directories), creates a specified number of directories with a dynamic directory name.Example 1: When executed as
./createDirectories.shday 1 90, it creates 90 directories asday1 day2 day3 ... day90.Example 2: When executed as
./createDirectories.shMovie 20 50, it creates 31 directories asMovie20 Movie21 Movie22 ... Movie50.
#!/bin/bash
#Assing Arguments
dir_name=$1
start_number=$2
end_number=$3
#Create Directories
for (( i=start_number; i<=end_number; i++ ))
do
mkdir -p "${dir_name}${i}"
done
echo "Directories created from ${dir_name}${start_number} to ${dir_name}${end_number}"
Task 2: Create a Script to Backup All Your Work:
- Backups are an important part of a DevOps Engineer's day-to-day activities. The video in the references will help you understand how a DevOps Engineer takes backups (it can feel a bit difficult but keep trying, nothing is impossible).
#!/bin/bash
src_dir=/home/ubuntu/scripts
tgt_dir=/home/ubuntu/backups
curr_timestamp=$(date "+%Y-%m-%d-%H-%M-%S")
backup_file=$tgt_dir/$curr_timestamp.tgz
echo "Taking backup on $curr_timestamp"
tar czf $backup_file --absolute-names $src_dir
echo "Backup Complete"
What is Cron?
Cron is a time-based job scheduler in Unix-like operating systems. It allows users to schedule jobs (commands or scripts) to run automatically at specified intervals. This could be anything from running a backup script every night at 2 AM, to sending out reminder emails every Monday morning, or cleaning up log files every hour.
Cron is started when the system boots up and runs in the background, checking the Crontab files to see if there are any jobs to execute.
What is Crontab?
Crontab (Cron table) is a configuration file that specifies shell commands to run periodically on a given schedule. Each user on a system can have their own Crontab file, allowing for personalized automation.
The Crontab file consists of a series of lines, each line representing a job, with the time and date fields followed by the command to be executed.
Crontab Syntax
A typical Crontab entry follows this format:
* * * * * command_to_execute
- - - - -
| | | | |
| | | | ----- Day of the week (0 - 7) (Sunday=0 or 7)
| | | ------- Month (1 - 12)
| | --------- Day of the month (1 - 31)
| ----------- Hour (0 - 23)
------------- Minute (0 - 59)
30 2 * * * /path/to/backup.sh
Editing Crontab
To edit your Crontab file, you use the crontab -e command. This opens your Crontab file in the default text editor, allowing you to add, modify, or remove jobs.
Copy codecrontab -e
To view your current Crontab entries, use:
Copy codecrontab -l
To remove all Crontab entries for the current user, use:
Copy codecrontab -r
Task 3: Read About Cron and Crontab to Automate the Backup Script:
- Cron is the system's main scheduler for running jobs or tasks unattended. A command called crontab allows the user to submit, edit, or delete entries to cron. A crontab file is a user file that holds the scheduling information.
- To take backup through crontab:
Crontab:
BACKUP TAKEN BY THE CRON JOB
Task 4: Read About User Management:
A user is an entity in a Linux operating system that can manipulate files and perform several other operations. Each user is assigned an ID that is unique within the system. IDs 0 to 999 are assigned to system users, and local user IDs start from 1000 onwards.
Create 2 users and display their usernames.
Why User Management Matters
User management in Linux is important for several reasons:
Security: Proper user management ensures that only authorized users have access to the system and its resources.
Organization: Different users can have different roles and permissions, keeping the system organized and efficient.
Resource Allocation: Managing users allows you to control resource allocation, ensuring fair usage and preventing resource hogging.
Basic Concepts
User Accounts
In Linux, a user account consists of several key components:
Username: The unique identifier for the user.
UID (User ID): A numerical ID assigned to the user.
Home Directory: The directory where the user's personal files and configuration settings are stored.
Shell: The command-line interface assigned to the user, typically
/bin/bash.
User Groups
Groups are used to manage multiple users with similar permissions. Each user can belong to one or more groups.
GID (Group ID): A numerical ID assigned to the group.
Primary Group: The main group associated with the user.
Secondary Groups: Additional groups the user belongs to.
Managing Users and Groups
Adding a User
To add a new user, use the useradd command:
sudo useradd -m username
- The
-moption creates a home directory for the user.
To set a password for the new user, use the passwd command:
sudo passwd username
Removing a User
To remove a user, use the userdel command:
sudo userdel username
To remove the user's home directory as well, add the -r option:
sudo userdel -r username
Modifying a User
To modify an existing user, use the usermod command. For example, to change a user's shell:
sudo usermod -s /bin/zsh username
To add a user to a secondary group:
sudo usermod -aG groupname username
Viewing User Information
To view user information, use the id command:
id username
This will display the user's UID, primary group, and secondary groups.
Adding a Group
To add a new group, use the groupadd command:
sudo groupadd groupname
Removing a Group
To remove a group, use the groupdel command:
sudo groupdel groupname
User Configuration Files
Linux user and group information is stored in several configuration files:
/etc/passwd: Contains user account information./etc/shadow: Contains hashed user passwords and password-related information./etc/group: Contains group information.
Example Entries
/etc/passwd:
username:x:UID:GID:User Info:Home Directory:ShellExample:
johndoe:x:1001:1001:John Doe:/home/johndoe:/bin/bash/etc/shadow:
username:hashed_password:last_password_change:minimum_age:maximum_age:warning_period:inactivity_period:expiration_date:reservedExample:
johndoe:$6$abcdefg$hijklmnopqrstuvwxyz:18475:0:99999:7:::/etc/group:
groupname:x:GID:membersExample:
developers:x:1002:johndoe,janedoe
Advanced User Management
Sudo Access
Granting a user sudo access allows them to execute commands as the root user. To add a user to the sudo group:
sudo usermod -aG sudo username
Password Policies
You can enforce password policies using the chage command. For example, to set a password expiration date:
sudo chage -E 2024-12-31 username
To set the minimum number of days between password changes:
sudo chage -m 7 username
Locking and Unlocking User Accounts
To lock a user account:
sudo usermod -L username
To unlock a user account:
sudo usermod -U username
