In this blog, we are learning about how to create backups by writing shell scripts, what is cron and crontab, and at last what is user management and how to create users.
- Create a script to back up all your work done till now.
#!/bin/bash
date_timestamp=$(date "+%Y-%m-%d-%H-%M-%S")
work_dir="/home/ubuntu/scripts"
tgt_dir="/home/ubuntu/backups"
backup_file=$tgt_dir/$date_timestamp.tgz
tar -cvzf $backup_file --absolute-names $work_dir
echo "Backup is taken on $date_timestamp"
echo "Backup is completed successfully"
So, let's break this script for better understanding:
In the first line, the date_timestamp variable is used to assign the date and time that is used in the echo command. "+%Y-%m-%d-%H-%M-%S", is the format of the timestamp.
In the second line, work_dir is the path of the folder which you want to backup.
In the third line, tgt_dir (target dir) is the path where we want to place the backup folder.
backup_file=$tgt_dir/$date_timestamp.tgz
In this line backup_file variable, I am giving the filename for backup with the .tgz (tar gunzip) extension.
In the fifth line, the tar command will make the zip file that will be created in the backup folder.
In the last two lines, the echo will print the statement.
What is Cron,Crontab ?
Cron is a software utility program that automates the scheduled tasks in a given specified time. It is a daemon process that runs in the background and performs the specified operations in a predefined time.
Crontab stands for cron table which is a list of commands that you want to schedule the tasks. It uses the job scheduler cron to execute the tasks.
It is configured in /etc/crontab.
Format of crontab :
M H DOM M DOW Command
M - Minute
H - Hour
DOM - Date of Month
M - Moth
DOW - Day of Week
Commands to list, edit, and remove the crontab :
crontab -l
This will list all the active crontabs on your machine.
crontab -e
After executing this command, it will ask in which editor you want to write (nano, vim, vi). This command is used to edit the crontab and write scheduled tasks.
crontab -r
This command will remove the job from the crontab.
crontab -u username -e
This command will edit the crontab from the other username.
User Management in Linux:
In Linux, a user can create, modify, and delete any files and can perform several other operations.
ID 0 is assigned to the Root user and from ID 1 to 999 are for system users and after that from 1000 id is assigned to local users. Each user has his own unique id that is assigned by the system.
The root is superuser that can access, and delete any files of any user.
- To add a user
sudo useradd Amit
sudo is the root, useradd is the command to add user "Amit"
- To get user id
id Amit
You will get three id's (uid) is the user id and (gid) is the group id and the last one is the groups id and all have same id number.
- To change the password of user.
sudo passwd Amit
passwd is the command to change the password of Amit user.
- To get list of all the users.
awk -F':' '{print $1}' /etc/passwd
awk command is used to extract the data from the file. Here by using awk command, -F is a file that is separated by : and prints the first column of the /etc/passwd file. (/etc is configuration files)
- To delete users
userdel Amit
Now, let's understand with example :
Create 2 users and just display their Usernames
useradd AmitMaurya
useradd Himanshu
These two commands will create the user Amit and Himanshu and to see whether these usernames are created or not you can execute them.
id Amit
id Himanshu
Or, you can see by awk command.
awk -F ':' '{print $1}' /etc/passwd
At last, you can the name of users that you had created.
So, That's it for the Day 5 Task. I hope you all have learned something and I am loving this #90DaysofDevOps challenge more day by day as I am learning also some new commands and topics.
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THANK YOU :)