Day 5: Advanced Linux Shell Scripting for DevOps Engineers with User management

Creating 'n' numbers of Directory using shell scripts:

Method 1:

This code creates directories named after the value of the "anytime" variable followed by a number from 1 to 90. The loop is set to run 90 times using the syntax "for ((i=1; i<=90; i++))", and the "mkdir" command is used to create a directory with a name composed of the "${anyname}" variable followed by the current value of the loop variable, denoted by "${i}".

Here we can modify the script by adding more variables as start and end and then apply loop for(( i=start; i<=end; i++)){}, we can either take the inputs for start and end as the arguments in the command line or put manually in the script file

Create a Script to back up all your work done till now:

• It prompts the user with a message "Do you want to create a backup?" using the "echo" command and reads the user's response using the "read" command, which stores the response in the "answer" variable.

• It then echoes back the user's response with the message "as your response is $answer, we will take backup".

• It takes the path to the file or directory to be backed up as an argument passed to the script, which is stored in the "path" variable.

• Finally, it creates a tar archive of the specified file or directory named "backup.tar.gz" using the "tar" command with the option "-cvzf".

It is shown in the image above.

Cron and Crontab, to automate the backup Script:

In Linux, the "cron" daemon is a service that allows users to schedule tasks (i.e., shell commands or scripts) to be run at specific times or intervals. The "crontab" command is used to create, modify, and view the user-specific cron schedules, called "crontabs". Here's an overview of the "cron" and "crontab" commands in Linux:

Cron: The "cron" daemon is a background process that runs continuously on the system and checks the "crontabs" of all users to see if any commands need to be executed at a particular time. Cron uses a configuration file called "crontab" to manage the schedule of commands.

Some steps are written below:

1. Create the backup script: First, create the backup script that you want to automate. For example, let's create a script called "backup. sh" that backs up a specific directory:

2. Schedule the backup script with Cron: To schedule this script to run automatically using "cron", follow these steps:

   • Open the crontab editor by running the command "crontab -e" in your terminal.

   • If prompted to select an editor, choose your preferred text editor.

     Add a new line to the crontab file with the following syntax:

     

     The string 0 2 * is a cron expression that specifies when to run the command. In this case, it means "run the command at 2:00 AM every day".

     0: The minute when the command should run (in this case, "0" means "at the start of the hour").

     2: The hour when the command should run (in this case, "2" means "2:00 AM"). : The day of the month when the command should run (in this case, "" means "every day"). : The month when the command should run (in this case, "" means "every month").

     : The day of the week when the command should run (in this case, "" means "every day of the week"). The command that follows the cron expression is /home/ubuntu/backup.sh /home/ubuntu /home/ubuntu/backup_directory. This means that the script located at /home/ubuntu/backup.sh will be executed, with /home/ubuntu as the source directory to be backed up and /home/ubuntu/backup_directory as the destination directory where the backup will be stored.

     So the overall meaning of this cron job is to run the backup. sh script at 2:00 AM every day, using the specified source and destination directories.

User Management:

In Linux, user management involves creating, modifying, and deleting user accounts and groups. Here are some commonly used commands for user management in Linux:

1. useradd: The "useradd" command is used to create a new user account.

2. passwd: The "passwd" command is used to set or change a user's password.

   Here are some common options for the "passwd" command:

   • "-l": Lock the user's account.

   • "-u": Unlock the user's account.

   • "-d": Remove the user's password.

Create 2 users and just display their Usernames:

If you are an Ubuntu user and do not have permission to add a new user you can see it as a user, I don't have permission to create a user because I don't have the power of Superman, like a super user called root.

To edit the visudo file, you need to have administrative privileges on the system. This means you must be a user with the sudoer's permissions or the root user.

Assuming you have the necessary permissions, you can edit the visudo file by following these steps:

1. Open the terminal on your system.

2. Type the following command and press Enter:

     sudo visudo
   

3. Make the necessary changes to the file. Be very careful while editing this file, as incorrect changes can cause serious problems with your system.

4. Once you have made the necessary changes, save the file and exit the editor.

Then you can try to create the same user as the above process mentioned.

Optionally, you can add the new user to any additional groups, such as the sudo group, by running the following command:

usermod -aG groupname username

Replace "groupname" with the name of the group you want to add the user to, and "username" with the name of the user you just created.

Now, If anyone wants to see all users:

This command will prompt a new window with all user details:

Thanks for reading :)

Shubham Jangale