Table of contents
No headings in the article.
Hello Everyone!
I have completed my Day 3 learning part. Please find my below Notes. Hope it will be helpful.
Concepts this Article covers:
Setting up an SSH client
SCP (Secure Copy)
User Management
Group Management
Linux File System Permissions
grep (Global regular expression print), find, awk
These are the topics that covered as part of Day3 learning. Please find below notes.
⬤ Setting up SSH client
SSH is a secure shell. A protocol typically used for connecting to Linux servers. The command-line SSH tool lets you log into your server and run commands remotely to perform any required task.
ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine. It is intended to provide secure encrypted communications between two untrusted hosts over an insecure network.
We can use ssh in windows. For that, it needs to be enabled. 👇
How to Enable and Use SSH Commands on Windows 10 (winbuzzer.com)
In AWS Linux, it will be already installed by default.
⬤ Connecting through SSH Client in windows CMD:
In windows, go to path where pem file is download and give command mentioned in SSH client page of aws -->ssh -i "NodePair.pem" ubuntu@ec2-3-110-182-104.ap-south-1.compute.amazonaws.com then enter
Here -i is for giving your pem file
⬤ SCP: Secure Copy
“secure copy” allows us to secure transferring of files between localhost and remote host or between two remote hosts.
Local host------------>Remote Hosts
sudo scp -i NodePair.pem localfile.txt ubuntu@ec2-3-110-182-104.ap-south-1.compute.amazonaws.com :/home/ubuntu/aasifa
⬤ User Management:
Creating users and groups.
#To check username who is currently logged in - whoami
#to add user, you need permissions to add user, -m creates users home directory
sudo useradd ayman -m
#to view if user is added
cat /etc/passwd
#setting up password for ayman user
sudo passwd ayman
#you cant enter into ayman by cd ayman, you either need to switch to ayman or give permissions
su ayman
⬤ Group Management
Creating a Group:
#we need few more users to add them to a group
useradd rosy
useradd jasmine
#first creat a group and name it then add all the users into it
sudo groupadd developers
#adding users into developers groups
#here -M overrides the group
sudo gpasswd -M ayman,rosy,jasmine developers
#here -M overrides the existing group
#to add a user to a group -a
sudo gpasswd -a ayman developers
#Now when we give permission to a group then it applies to all the users inside it.
#to remove a user from the group
sudo gpasswd -d ayman developers
#to delete the group
sudo groupdel developers
⬤ Linux File System Permissions
We can set permission as below
- chmod u+r /filename (here giving read permission to the user for the file)
you can also give as
chmod g+rwx/filename
#to remove permission
chmod g-rw/filename
chown:
#To change ownership of the directory or a file
sudo chown jasmine testfile.txt
- We can set permission using numeric values also
r(read) - 4
w(write) - 2
x(execute) - 1
#giving rwx permissions to user, rx to group, x to others
sudo chmod 750 testfile.txt
#Other is every one that is not the owner or in the group.
For example, if you have a file that is root: root then the root is the owner, users/processes in the root group have group permissions, and you are treated as other.
⬤ ACL : (Access Control List)
#To work with ACL you need to install it
sudo apt install acl
Hadoop - File Permission and ACL(Access Control List) - GeeksforGeeks
permissions only for the owner, one group, and others for any share point or folder or file. ACLs allow you to grant permissions to multiple individuals or groups on a shared item.
Unlike the basic and regular way of giving permissions to one user that is the owner of a file and one group that is the group owner of a file using the “chmod” command, if you have to give additional permissions to another user or another group on a file without making the user a member of the group, you will have to use ACL to do it.
When permission is set on a file or directory using ACL, it displays a “+” sign when a list command is used.
Lets say I have 3 users ayman, rosy and jasmine and a group developers
#checking if permissions applied to the folders,users and group using getfacl using ACL
Lets create a directory and add users into it
#we added users in acldir
#first check permission in acldir
#Now give permissions to acluser1 which was created under acldir
#set read and execute permission to the acluser1 which is a user present in acldir
setfacl -m u:acluser1:rx acldir
#check if permissions applied or not
getfacl acldir
#Now create a group " aclgrp " and add all these aclusers1,2,3 into it
#giving rwx permission to aclgrp
⬤ grep (global regular expression print)
Here regular expression is used to search data, matching complex patterns
#Install grep if you don't have
sudo apt-get install grep
You can search in a particular folder or a file
Examples:
grep devops /home/ubuntu -- displays devops word in ubuntu folder
grep INFO test.txt
#search the string in output of first command
cat sample.txt | grep [options] string
Options Description
-c : This prints only a count of the lines that match a pattern
-h : Display the matched lines, but do not display the filenames.
-i : Ignores, case for matching
-l : Displays list of a filenames only.
-n : Display the matched lines and their line numbers.
-v : This prints out all the lines that do not matches the pattern
-e exp : Specifies expression with this option. Can use multiple times.
-f file : Takes patterns from file, one per line.
-E : Treats pattern as an extended regular expression (ERE)
-w : Match whole word
-o : Print only the matched parts of a matching line,
with each such part on a separate output line.
-A n : Prints searched line and nlines after the result.
-B n : Prints searched line and n line before the result.
-C n : Prints searched line and n lines after before the result.
Interview Question:
To know if user is created or not use
sudo grep ayman /etc/passwd
Find:
The Major difference is FIND is for searching files and directories using filters while GREP is for searching a pattern inside a file or searching process(es).
Find can perform,
searching by file, folder, name, creation date, modification date, owner and permissions.
Syntax:
find [where to start searching from] [-options] [what to find]
examples:
#it will find(display) name of the file called example.txt in the current dir
find . -name example.txt
#it will find all the files which are .jpg files in the home dir
find /home -name *.jpg
-exec CMD: The file being searched which meets the above criteria and returns 0 for as its exit status for successful command execution.
-ok CMD : It works same as -exec except the user is prompted first.
-inum N : Search for files with inode number ‘N’.
-links N : Search for files with ‘N’ links.
-name demo : Search for files that are specified by ‘demo’.
-newer file : Search for files that were modified/created after ‘file’.
-perm octal : Search for the file if permission is ‘octal’.
-print : Display the path name of the files found by using the rest of the criteria.
-empty : Search for empty files and directories.
-size +N/-N : Search for files of ‘N’ blocks; ‘N’ followed by ‘c’can be used to measure size in characters; ‘+N’ means size > ‘N’ blocks and ‘-N’ means size < ‘N’ blocks.
-user name : Search for files owned by user name or ID ‘name’.
\(expr \) : True if ‘expr’ is true; used for grouping criteria combined with OR or AND.
! expr : True if ‘expr’ is false.
awk command:
Top 20 AWK Command in UNIX/LINUX with Examples [Updated] (hackr.io)
Used to make segments of the output. $1 prints the first column of df - H output.
