Day 5 of #90DaysOfDevOps with the #TrainWithShubham Community. The challenge is for the DevOps Community to get stronger in #DevOps. It is a great initiative by Shubham Londhe. Documenting my learning and also sharing it with the community is helping me to get more clear with the concepts.

1. Write a bash script createDirectoriess1.sh that when the script is executed with three given arguments (one is the directory name and second is the start number of directories and the third is the end number of directories ) it creates a specified number of directories with a dynamic directory name.

• Use shell scripting and take the input as an argument from the user.

Scenario 1: Creates 90 directories as day1 day2 day3 .... day90

Scenario 2: Creates 50 directories as Movie20 Movie21 Movie23 ...Movie50

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

• Write a shell script, whenever this script runs it back up the source file to the backup directory as a tar file and the name would be the time stamp when it runs.

Output:

*tar xvf use to extract the tar file.

3. Read About Cron and Crontab, to automate the backup Script

The cron is a software utility, offered by a Linux-like operating system that automates the scheduled task at a predetermined time. It is a daemon process, which runs as a background process and performs the specified operations at the predefined time when a certain event or condition is triggered without the intervention of a user.

The crontab is a list of commands that you want to run on a regular schedule, and also the name of the command used to manage that list. Crontab stands for “cron table, ” because it uses the job scheduler cron to execute tasks. The schedule is called the crontab.

• To view the Crontab entries

  crontab -l

  View Root Crontab entries: Login as root user (su – root) and do crontab -l

  To view the crontab entries of other Linux users: Log in to root and use crontab -u {username} -l.

• To edit Crontab Entries

  rontab -e

Crontab Fields and Allowed Ranges (Linux Crontab Syntax)

Field    Description    Allowed Value
MIN      Minute field    0 to 59
HOUR     Hour field      0 to 23
DOM      Day of Month    1-31
MON      Month field     1-12
DOW      Day Of Week     0-6
CMD      Command         Any command to be executed.

Linux Crontab Format

MIN HOUR DOM MON DOW CMD

Output:

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 for each user in the operating system.

The ID 0 is assigned to the root user and the IDs 1 to 999 (both inclusive) are assigned to the system users hence the ids for local user begins from 1000 onwards.

To list out all the users in Linux

awk -F':' '{ print $1}' /etc/passwd

Using id command, you can get the ID of any username.

id username

The command to add a user.

sudo useradd username

Using passwd command to assign a password to a user

passwd username

5. Create 2 users and just display their Usernames.

Output:

Thank you.