Linux Commands with Explanation.

• mkdir - Create a new directory

    mkdir new_directory name
  

• mkdir new_direactory name or folder name

    mkdir Shivarajughm
  

mkdir -vp Shivarajughm

• m --> Sets the access mode for the new directory.

• -p--> If the parent directories don't exist, this command creates them.

• -v--> Print a message for each created directory

mkdir -vp Shivarajughm/Linux/ShellScript/Git/Maven/Tomacat/SonarQube

The touch command creates an empty file with zero bytes.

touch devops.txt

touch file1 file2 shiva.txt

cd - Change directory

cd Shivarajghm

To come out of a present directory

cd - it will take a working directory

cd -

If you want to go home directory

cd ~

If you want to go 3 levels up

cd ../../..

If you want to come out of 2 or more directories.

cd ../../

To move to the absolute path.

  cd /shivarajughm1/shivarajughm2/

cd /home/user/

PWD - Print the current working directory

pwd

vi :- it is the create file & update the file.

it is going open in the command mode press the i --> it will comes insert mode.

press esc I – insert mode in vi editor.

after that, we enter the details. then we have to the save file.

Press esc: wq! – save and quit the file. W-write,q-quit,!-forcefully.

Press esc: q! – quit without saving the content.

Press esc: set number or se nu – which sets the number for a file.

vi devops.txt
 Hi hello 
 how are you

Awk command :- it Is used to cut the content of a file column-wise.

you can see this is also the same all the content in the file I want to print that particular only first color $0,$1,$N these are field variables.

vi ghmfamily.txt

cat ghmfamily.txt
=============================================================
FirstName    LastName      SurName       Occupation    Place
=============================================================
Mahanandi     Swamy          GHM         Business      Gulyam
Sreedevi       ---           GHM         House Wife     NDM
Shivaraju     Swamy          GHM        DevOps engi    Bangalore
Divya         Swamy          GHM         D.e.O           Ballari 
basava        Swamy           HM         G.R.B           Ballari
Pooja         swamy          GHM         student         Ballari 
==================================================================

awk '{print $(NF)}' ghmfamily.txt
awk '{print $(NF-1)}' ghmfamily.txt
awk  ‘{print $2,$3}’ filename  -2nd and 3rd col 
Ls –lrt | awk  ‘{print $NF}’  –last col 
Ls –lrt | awk  ‘{print $2,$3}’ 
Ls –lrt | awk ‘{print $(NF-1)}’ -2nd last col 
awk '{print}' ghmfamily.txt 
awk '{print $0}' ghmfamily.txt  
awk '{print $1}' ghmfamily.txt 
awk '{print $2}' ghmfamily.txt 
awk '{print $3}' ghmfamily.txt 
awk '{print $1,$2,$5}' ghmfamily.txt

• ls --> Lists the contents of your current working directory.

• Some options with ls are :

  -l --> list in long format

  -a--> all files including those which begin with dot

  -F--> It is used to classify the directories and executables. It will append indicator (one of */=>@|) to entries

  -i --> list the inode number in the first column

  -R--> recursively list all directories and subdirectories

  -r--> Display in reverse order.

  -t--> sorts files by access time.

  Files start with : ( – )

  Directories start with : ( d )

  Links start with : ( l )

  list files and directories with long ( It will show in alphabetical)

    ls –l
  

  Long list format with time

    ls –lt
  

  it will display reverse-order files and directories.

    ls –lrt
  

  it will display a list of the hidden files

    ls -a
  

  rm - Remove a file or directory:

    rm file.txt or rm -r directory
  

rmdir --> This command is used to remove the directory.

rmdir directoryname

it is going to all directories & all files in the current directory

rm -rf *

cp - Copy a file or directory:

cp file.txt /home/user/ or cp -r directory /home/user/

mv - Move or rename a file or directory:

mv file.txt /home/user/ or mv oldname.txt newname.txt

cat - used to display the content of a file on the console.

cat shivarajughm.txt

less - Display the contents of a file one page at a time

less file.txt

tail - Display the last few lines of a file

tail filename.txt or tail file1 file2 file3

head - Display the first few lines of a file:

head file.txt or head file1 file2 file3

Grep: Is used to search pattern/string in a file without opening the file/console

grep 'pattern' file.txt

Grep  “pattern” filename

Grep –w “pattern” filename           It is used to search only word

It will give the pattern present in all the files.

Grep pattern *

prints only file names whose pattern is present

Grep –l  “pattern” *

Grep –R –l  “pattern” * or rgrep “pattern” file

used to count number of lines. Give the count of the pattern in the files.

Grep –c  “pattern” *

used to search multiple patterns Also u can use egrep “pattern1” , “pattern2”

Grep –e “pattern1” –e “pattern2” * or egrep "pattern1","pattern2"

used to print all lines starting with w from the given file

Grep  ^w filename

used to print all lines which end with pattern e from the given

Grep  e$ filename

Pipe filters (|):- Pipe is used to give an output of one command as the input to the next command.

ls –lrt > log.txt | cat log.txt

FIND: using the find command we can search the file search directories with various conditions.

How to find the empty files in the current directory, find. (dot) represent in the Linux

find . -type f -empty

how to find home directory

find ~ -type f -empty

if you want to search the entire file system uses the root directory

find / -type f -empty

tar - Create or extract a tar archive

tar -cvf archive.tar file.txt or tar -xvf archive.tar

gzip - Compress or decompress a file

gzip file.txt or gzip -d file.txt.gz

curl - Transfer data from or to a server

curl https://example.com/

wget - Download a file from the web

wget https://example.com/file.txt

Ping:- Is used to check whether the server is up or down.

Ping - Test network connectivity

Ping ip or  ping hostname

traceroute - Trace the path taken by packets over the network:

traceroute example.com

ssh - Connect to a remote server securely

ssh - it is used to connect to a remote server.

ssh user@example.com
ssh user-name@host-name/IP(servername)

scp - Copy files securely between hosts or it Is used to copy files or dir from one server to another server.

Scp file username@server2:/home/dir1/dir2/
Password: abc@123#**
Scp –r dir1 username@server2:/home/../../
Scp –p file1 username@server2:/home/../../
        P is preserved permission as same
scp file.txt user@example.com:/home/user/

Rsync:- it is used to copy files from one server to another server and also within the server, while copying the data if a copy is stopped due to network issues in between, if I use ‘scp’ it will start copying from begin if I use rsync it will start copying from where it is stopped.

rsync :- Synchronize files and directories between hosts

rsync file username@server2:/home/test/../
rsync -avz file.txt user@example.com:/home/user/
rsync src dest

TOP:- Display system processes and their resource usage

The top utility is a commonly used tool for displaying system-performance information. It dynamically shows administrators which processes are consuming processor and memory resources.

ps - Display information about running processes:

ps -ef | grep service name

kill - Send a signal to a process to terminate it

kill process id

netstat - Display network connections and their status:

netstat -an

ifconfig - Display network interface configuration:

ifconfig

route - Display or modify the kernel's routing table:

route -n

iptables - Configure firewall rules:

iptables -l

hostname - Display or set the hostname of the system:

hostname or hostname new_hostname
hostname -i

name - Display system information:

uname -a
uname -v

free - Display memory usage:

free -m
free -h 
free -g 
free -k

df - Display disk space usage:

df -h

du - Display disk usage by directory:

du -sh /home/user/

1) Permissions

2) Number of links

3) Owner

4) Group Owner

5) Size of the File in Bytes

6) Date and Time of created

7) File name/Dir Name

Access Permissions Chmod command

Used to change permission of a file or directory

-r-- r-- r-- :- file or directory or link,

rwx=user, r--=group, r--=others R=read,w=write,x=execute

It will be in binary format r=4. w=2. x=1

umask -->user mask is used to set the permission for files/directories.

once created with directory 755 permissions

same way default file permissions set

r --> read -->4

w --> write-->2

x--> execute-->1

we are getting 775 permissions

421 421 4-1

rwx rwx r-x

Chmod 777 filename              – all permission to a file

Chmod u+w file –user and write permission to a file Group and other full permission 277

chmod u+w file 277
Chmod g+rwx,o+rwx file 077   (+ Adding the permission)
Chmod g-w,o-w file 722       (- Removing the permission)
Chmod a+rwx file 777
chmod 644 file.txt or chmod -R 755 directory/

chown - Change the owner of a file or directory

chown user file.txt or chown -R user directory/