# Advanced Linux Shell Scripting for DevOps Engineers with User management

### ***Create 5 directories at a time using scripting. Instead of creating it manually one by one make a use of for loop which will create it in one go within a second.***

So we are passing three arguments here. **variable1** is the name of the directory, **variable2** is the number from where the directory will start and **variable3** is the number where the directory will end.

Script:

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1688572074459/55fa9d67-a5f4-41b5-b4d8-6a2e46e31b6a.png align="left")

op:

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1688572125571/0a4d4427-54ca-45cc-9fe2-ecd86ec4668f.png align="left")

### ***Read about cron and crontab***

* 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.
    
* The Cron daemon is a background process/service 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.
    

Create a backup script:

For example, let's create a script called "[**backup. sh**](http://backup.sh/)" that backs up a specific directory:

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1688572595516/7a908166-0c92-459a-9489-9c5c110028d7.png align="left")

Schedule the script using cron. Follow below mentioned steps for it:

* 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:
    
* ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1688572619860/0d861ce0-30ef-491d-9474-fd7142e0b507.png align="left")
    

In the crontab file:

m- minutes

h- hour

dom- day of the month

mon- month

dow- day of the week

where \* means every. For example every minute, every hour

In the above example, 0 implies at the start of the hour

2 in hour means "2:00 AM"

The command that follows the cron expression is /home/ubuntu/[backup.sh](http://backup.sh/) /home/ubuntu /home/ubuntu/backup\_directory. This means that the script located at /home/ubuntu/[backup.sh](http://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**](http://backup.sh/) script at 2:00 AM every day, using the specified source and destination directories.

crontab -e **Use the crontab -e command to open your user account's crontab file**

For checking use: crontab -l

### ***Create user***

To add the user to the Linux system use: useradd user\_name

To set the password use: passwd user\_name

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1688573097462/49b88ca5-74f9-4ce2-81c4-11f106d54704.png align="left")