ls To see the details of your list.

ls -ltr

The ls -ltr command is a combination of options used with the ls command in Unix-like operating systems (such as Linux). Here's a breakdown of the options:

• ls: This is the command used to list files and directories in a directory.

• -l: This option enables the long format, providing detailed information about each file or directory, including permissions, owner, group, size, modification date, and name.

• -t: This option sorts the list of files by modification time, with the newest files appearing first.

• -r: This option reverses the order of the sort, displaying the oldest files first.

Delete a directory

rmdir "directory_name"

To see zip file content

zcat "file_name"

To display the first few lines of your file in your big file,.

head "file_name"
head -n 5 "file_name"   # it will show top 5 lines

To display the last few lines of your file in your big file,

tail "file_name"
tail -n 5 "file_name"   # It will show bottom 5 lines

To see the live bottom five lines,.

tail -f "file_name"

To see a file in a page format. less make small, small pages.

less "file_name"

more also like less.

more "file_name"

Copy a file from a specific directory and paste it into that directory.

cp devops/lol.txt cloud/
# copy a folder with all file to another folder
cp -r "src_folder/ destination_folder/"
#move a folder to another folder
mv "src_folder/ destination_folder/"

Count the words in your files.

wc "file_name"   # wc = word count

1. Count lines, words, and characters in a file:

    wc filename
   

   This will output three numbers: the number of lines, words, and characters in the file.

2. Count only the number of lines:

    wc -l filename
   

   The -l option tells wc to count only the number of lines.

3. Count only the number of words:

    wc -w filename
   

   The -w option tells wc to count only the number of words.

4. Count only the number of characters:

    wc -m filename
   

   The -m option tells wc to count only the number of characters (this includes newline characters).

5. Count only the number of bytes:

    wc -c filename
   

   The -c option tells wc to count the number of bytes in the file.

6. Count words in multiple files:

    wc file1 file2 file3
   

   This will display the line, word, and character counts for each file and then provide a total count at the end.

7. Combine options: You can combine options to get specific counts. For example, to get the number of lines and words:

    wc -lw filename
   

8. Count from standard input: You can also use wc with input from another command or from the standard input:

    echo "Hello World" | wc -w
   

   This will output 2 because there are two words in "Hello World".

Here's an example output of wc:

wc example.txt
10  50 200 example.txt

This output indicates that example.txt contains 10 lines, 50 words, and 200 characters.

By using these options, you can effectively count lines, words, characters, and bytes in files or input streams in Linux.

Hardlink and softlink

Links are shortcuts. As in our Windows system, we use any application shortcut icon on our desktop.

Hardlink is responsible for lifetime service. If the main file is deleted, then hardlink will also work for operations.

Softlink is deleted if the main file is deleted.

To make a soft link:

ln -s "specific_path/file_name" "softlink_name"

To make hardlink

ln "specific_path/file_name" "hardlink_name"

cut is command to cut a specific amount of byte.

cut -b 1 "file_name"  #It will cut first byte
cut -b 1-4 "file_name"  # It will cut first 4 bytes

Now create a file using echo then print it and save it as a file.

echo "This is a file" | tee "new_file_name"

sort lines accordingly alphabetically

sort "file_name"

To see differences between two files.

diff "file_name" "file_name"

To see disk usages storages and so on

df
df -h   # high level disk storages
du .  # perticular folder related storages

Total process

top

Particular bash running in which ID

ps
ps aux       #totall information view.

fuser

To kill any process

kill -9 "ID"

Total Disk spaces

free
free -h

Application logs store in a file

nohup "used_command"
#Example: use free -h command and store the outputs by using nohup command
nohup free -h
# To see the saved logs file 
cat nohup.out

To see virtual memory

vmstat
vmstat -a

Linux for DevOps

System-level Commands

To see which platform do you use.

uname

To see how many times your system is running.

uptime

To see user ID or user group ID

id

The apt command is a package management tool used in Debian-based Linux distributions, such as Ubuntu. It is used to manage software packages on the system. Here are some common apt commands:

1. Update Package List:

    sudo apt update
   

   This command refreshes the local package list, pulling in information about available package updates.

2. Upgrade Packages:

    sudo apt upgrade
   

   This command installs the latest versions of the packages on your system.

3. Install a Package:

    sudo apt install package_name
   

   This command installs a new package on your system.

4. Remove a Package:

    sudo apt remove package_name
    sudo apt remove docker.io  #Example
   

   This command removes a package from your system while keeping its configuration files.

5. Remove a Package and Its Configuration Files:

    sudo apt purge package_name
   

   This command removes a package along with its configuration files.

6. Search for a package:

    apt search search_term
   

   This command searches for packages matching the specified search term.

7. Show Package Information:

   
    apt show package_name
   

   This command displays detailed information about a specific package.

8. Autoremove Unused Packages:

    sudo apt autoremove
   

   This command removes packages that were installed as dependencies for other packages but are no longer needed.

These are just a few examples of the apt command. Depending on your specific needs, there are many other options and variations available. Always use sudo with apt commands to execute them with administrative privileges.

yum     # For CentOS
dnf     # For Fedora
pacman  # For Arch
rpm     # Redhat
portage # For Gentoo Linux and also ChromeOS

User and Group management Commands

The useradd command in Unix-like operating systems, including Linux, is used to create a new user account. The -m option, when used with useradd, ensures that a home directory for the new user is created. Here's the basic syntax:

sudo useradd -m "username"

Explanation:

• sudo: Run the command with superuser (root) privileges.

• useradd: Command used to add a new user.

• -m: Create the user's home directory if it doesn't exist.

After running this command, a new user account will be created with the specified username, and a home directory will be created at /home/username. Note that you might need to set a password for the new user using the passwd command after creating the account:

sudo passwd username

Replace "username" with the desired username for the new user.

The su command stands for "substitute user" or "switch user." It allows you to change to another user account in the current shell session. If you want to switch to a specific user account, you can use the following command:

su "username"
or
su - "username"

Replace "username" with the name of the user account to which you want to switch. After entering this command, you might be prompted to enter the password for the specified user.

To display all users lists

cat /etc/passwd  # Look at the last portion

To delete a user

sudo userdel "username"

To create a usergroup

sudo groupadd "group_name"

To display all group lists

cat /etc/group  # Look at the last portion

To add a user to a group.

sudo gpasswd -a "username" "group_name"

To search any commands in linux cli click contr + r

To add multiple users to a group.

sudo gpasswd -M "first_username", "second_username","third_username" "user_group_name"

-M means multiple users.

To delete a user group,.

sudo groupdel "group_name"

File permissions commands

chmod 777 "filename/foldername"

In computing, umask is a command that determines the settings of a mask that controls how file permissions are set for newly created files. It may also affect how the file permissions are changed explicitly. umask is also a function that sets the mask, or it may refer to the mask itself, which is formally known as the file mode creation mask. The mask is a grouping of bits, each of which restricts how its corresponding permission is set for newly created files. The bits in the mask may be changed by invoking the umask command.

umask         # display current value (as octal)
0022
umask -S      # display current value symbolically
u=rwx,g=rx,o=rx
umask -p      #

Symbolic and Numeric umask Values

As we mentioned in the example above, umask can be displayed as a numeric (octal) or symbolic value.

A mask can have the following numeric, and the corresponding symbolic, values:

To change the user ownership of a file.

sudo chown "username" "filename"

To change the group of a file.

sudo chgrp "groupname" "filename"

Compression commands

sudo apt install zip

To zip a folder

zip -r "new_zip_foldername" "dedicated_filder"   # If folder then use -r
#For unzipeed
unzip "file_name"

Compress a folder or file by using the tar command.

tar -cvzf "new_filename" "dedicated_file/folder"  #To compress c = compress. v =Display the verbose informations.
                               # z = Uses gzip compression. f = Specify the file name.

To extract the zip file or folder

tar -xvzf "zip_file/foldername"

File transfer Commands

To send a file from a local to a remote server.

scp -i "Users/nur/Downloads/mohammad.pem" "dedicated_filename" ubuntu@ec2-3-15-221-86.us-east-1.compute.amazonaws.com:"where you want this file in your remote server like- /home/ubuntu"

Now copy a folder from the remote server to the local server.

scp -i "Users/nur/Downloads/mohammad-key.pem" -r ubuntu@ec2-3-15-221-86.us-east-1.compute.amazonaws.com:"/home/ubuntu/'folder_name' ."

To add a local file to your local. It will not be on a remote server. In this case, we can use the rsync command.

Firstly, install rsync. And importantly need ssh connection.

rsync -e "ssh -i /Users/nur/Downloads/mohammad-key.pem" -avz "foldername_fromlocalserver" ubuntu@ec2-3-15-221-86.us-east-1.compute.amazonaws.com:/home/ubuntu/'folder-name'

Networking Commands

To check network working or not.

ping "IP_Address"/"Web_address"

Network statics

sudo apt install net-tools
netstat         # Active internet connections, ports. local and foreign IP's.

Network Interfaces

ifconfig

sudo apt install traceroute
sudo apt install inetutils-traceroute
traceroute youtube.com
tracepath youtube.com       #To see specific path

Note: To search IP address: https://whatismyipaddress.com/ip-lookup

ping and tracepath command togather.

mtr mmohamm5.github.io     # mtr = my trace route.

nslookup mmohamm5.github.io

telnet mmohamm5.github.io 80

To see hostname

hostname mmohamm5.github.io
cat /etc/hosts

ip address show

To see Wireless connections

sudo apt install wireless-tools
iwconfig

Another network statics show command like netstat is ss

ss

to see details in an application

dig mmohamm5.github.io

To see domain name and registry

sudo apt install whois
whois mmohamm5.github.io

nc mmohamm5.github.io 80

To find mac address

arp

Interfaces running or not

suod apt install ifplugd
ifplugstatus

To call API's end point

curl -X GET https://dummy.restapiexa,ple.com/api/v1/employees | jq
# if it not work then install jq
sudo apt install jq

To download anything from internet

wget https://file-examples.com/wp-content/storage/2017/02/file-sample_100kB.doc

sudo iptables

To watch any specific commands. Every two seconds, it will show the result.

watch mtr mmohamm5.github.io   # By default it will run every in two seconds.
watch -n 5 mmohamm5.github.io   # It will run every 5 seconds.

Network map

sudo apt install nmap
nmap -v mmohamm5.github.io