Linux Commands:

1. System Basic Commands
   
2. Processes Commands
   
3. File Commands
   
4. Permissions Commands
   
5. Searching Commands
   
6. Link Commands
   
7. Compress Commands
   
8. Job Schedule Commands
   
9. File Transfer Commands
   
10. Root Commands

Root command:
=============

useradd user_name  //add new user
passwd user_name //password set and change password
userdel user_name //delete user
cat /etc/passwd  //list all users
su - user_name  //switch user
su user_name
su   //switch root user
logout
exit
# --> root user
$ --> normal user

Manual Command:

man command
example:
man useradd  //exit manual pages press 'q'

System basic Commands:
=======================

IP Commands:
============
hostname
hostname -i  //Display the IP address(es) of the host
ifconfig
hostname -a  //Display the alias name of the host
hostname -d  //Display  the name of the DNS domain

OS Commands:
============
uname
uname -a
arch
cat /etc/redhat-release

Date Commands:
==============
date
date +%a //locale’s abbreviated weekday name (e.g., Sun)
date +%A //ocale’s full weekday name (e.g., Sunday)
date +%b //locale’s abbreviated month name (e.g., Jan)
date +%B //locale’s full month name (e.g., January)
date +%d //day of month (e.g, 01)
date +%D //date; same as %m/%d/%y
  F //full date; same as %Y-%m-%d
  u //day of week(1 is monday)
  U //week number of year
  H //hours(00..23)k(0..23)
  I //hours(01..12)l(1..12)
  M //minute
  S //seconds
  m //month
  Y //year(2020)y(last 2 digit(20))

Calendar Commands:
==================
cal  //current month calender
cal 2010 //2010 calender
cal 5 2010 //2010 may month calender
cal -3 //Display prev/current/next month output.

Disk Commands:
==============
du dir_name or file_name //bytes in file space usage
du -h //human readable
df
df -h
free  //free and used memory in the system
free -b  //bytes
free -k  //KB
free -m  //MB
free -g  //GB

User Commands:
==============
logname  //name of the current user
whoami //name of the current user
who am i //current user name and login time
who  //show who is logged on
who -u //show who is logged on with ip address
id //user  and group information
users //user names of users currently logged in to the current host
groups //group memberships for each username
groups group_name
uptime //Tell how long the system has been running
w //Displays information about the users currently on the machine and their processes
========================================================
wall //Send a message to everybody's terminal

history  //System Basic CommandhistoryDisplay the command history list
history -c //clear the history
clear //Clear the terminal screen

alias clr=clear //create alias string for command with option
alias //list of all alias
unalias clr  //remove alias

expr 10 + 20 //addition,sub,mul,devision,models

seq 10 //Display a sequence of numbers
seq 1 10
seq 2 2 10

vmstat
iostat
netstat
sleep 10 //Pause for a specified amount of time(seconds)
ping
echo 'welcome'

Process Commands:

=================

ps  //current session processes
ps -ef //list of all processes
ps -ef|grep postgres
ps -ef|grep pmon
pstree  //Display a tree of running processes.
kill -9 2342 //Terminate a process(2342 is pid)
top  //Display a dynamic real-time view of a  running linux kernel.
cat /proc/cpuinfo //display the cpu information
cat /proc/meminfo //display the memory information

File Commands:
==============

ls  //listout directory and file name only
ls -l or ll  //long listing
ls -lrt or ll -rt //reverse order use time
ls -lS or ll -S //sort by file size
ls -la or ll -a //listout hidden files and directory
==================================================
pwd  //current/working directory
cd //default home directory
cd directory_name //open directory
cd .. //change back to one step
cd - //change previous path
cd /dir_1/dir_2/dir_3/dir_4
vdir -l /sample/ //list the directory
================================================
mkdir dir_name //create a directory
makdie dir_1 dir_2 dir_3 //create a multiple directory
mkdir -p /dir_1/dir_2/dir_3/ //create a Parental with Subdirectory
===============================================
cat  //concatenate
touch
vi editor
nano
===============================================
cat:(only file create,add text and extra add text)
====
cat > file_name  //create a new file
cat file_name
cat >> file_name //add text
cat file_1 > file_2 //copy file
cat -n file_name //number all output lines
tac file_name //reverse
============================================================
touch:(create single,multiple empty file and change file timestamps)
======
touch file_empty
touch f1 f2 f3
touch -t 2001011230 file_name //use YYMMDDhhmm instead of current time
================
vi editor:
===========
command mode
insert mode
escape mode

vi filename

command mode:(press esc)
=============
gg //cursor goes to first lines
shfit + g  //cursor goes to last line
10gg //cursor goes to 10th line
yy //current line copy
3yy  //3 line copy
pp //paste
dd //delete the line
5dd  //delete five lines
dw //delete single word
d5w  //delete 5 words
x //delete single letter
10x  //delete 10 letters

Insert Mode:
============
(press any one a,s,i,o letter to insert)

Escape Mode:(press Esc + :)
============
w //only save file
q //unsave and quit(exit file)
! //force
wq //save and quit
wq!  //force save and quit

find and replace:
=================
%s/source_text/target_text/g
=========================================================
copy command:
=============
cp f1 f2 //copy file f1 to file f2
cp oldfile /home/siva/newfile
cp -rf f1 f2
cp -R /home/siva/d1 /home/muthu/d2
nohup cp -rf /zzz/ /xxx
cp -rf /zzz/ /xxx &  //background copy
jobs //list background process
Move Commands:
==============
mv old_file new_file
mv old_file /home/siva/newfile
mv /home/muthu/d1 /home/siva/d2

Remove Commands:
================
rm filename
rm -rf filename
rmdir dir_name //remove empty directory
rm -rf dir_name //directory which have contents

head and tail commands:
======================
head file_name  //display first 10 lines
head -5 file_name //display first 5 lines
tail file_name  //display last 10 lines
tail -5 file_name //display lst 5 lines
head -6 file_name|tail -2 //display 5th and 6th line only
cat file_name|head -6|tail-2

word commands:
==============
wc file_name //list of lines,words,letters
wc -c filename //show letters only
wc -l file_name //show lines only
wc -w file_name //show words only

less filename
more file_name
nl file_name //number lines of file
sort file_name //sort lines of text files
sort file_name|uniq  //remove duplicate text

comm file_1 file_2
diff file1 file2
diff3 f1 f2 f3
cmp f1 f2  //compare two files byte by byte
dd if=f1 of=f2 conv=ucase //Data duplicator and used for copying and converting data.

==============================================================

Searching Commands:
===================

locate
find
awk
grep

locate:
=======
locate file_name //find files by name

find:
=====
find -name file_name //find file_name
find . -name file_name
find -iname file_Name //find file ignoring case
find -size 10M
find -empty
find -size 0c
find -amin -5 //last accessed 5 min
find -atime -1 //last accessed 1 day
find -cmin -5 //File’s status was last changed 5 minutes ago.
find -ctime -1 //File’s status was last changed 1 day ago.
find -mmin -3 //last modified 3min
find -mtime -1 //last modified 1day

grep:(print lines marching a pattern)
=====
grep muthu file_name //select  matching  lines
grep -v 'muthu' file_name //select  non-matching  lines
grep -i 'muthu' file_name //ignore-case
grep -c 'muthu' file_name //count lines
grep --color 'muthu' file_name
cat file_name|grep -c muthu

awk:
====
awk {'print $1'} file_name
ls -l|awk {'print $9'} file_name

===============
sed 's/muthu/pearl/' file
sed 's/muthu/pearl/' file > file2
cat file|tr 's' '$'
ls -lrt|cut -d ':' -f2
which file_name
whereis file_name

Permission Commands:
====================

groupadd group_name
groupdel group_name
cat /etc/group
chgrp group_name file_name
usermod -g group_name user_name

chmod u+x file_name
chmod g-r file_name
chmod o+w file_name
umask
chmod 755 file_name
chmod -R 755 file_name
chown user_name file_name
chown -R user_name file_name
chown -R user_name:group_name file_name
chown -R user_name. file_name
=============================================

Link Commands:
=============

symbolic links or soft link //file and directory  f1 f2 f3 f4 remove f3 not working f4
hard link //file only  f1 f2 f3 f4 remove f3 working f4
===
soft:
======
ln -s file_1 file_2
ln -s dir1 dir2

hard:
=====
ln file_1 file_2
ls -li
================================================

Compress Commands:
==================

zip  //files & dir  //65% compress
gzip //only file to move  //65% compress
tar  //file or folders to file //no compress

zip file_name.zip file_name
zip -r dir.zip dir_name
zip -e dir.zip dir_name  // Password Protected ZIP file
zip -s 1g -r archivename.zip directory_name //splite file 1gb
unzip file_name.zip
unzip dir.zip

gzip file_name
gunzip file_name.gz

tar -cvf file_name.tar file_name
tar -cvf dir_name.tar dir_name
tar -xvf file_name.tar
===================================================

Job scheduling commands:
=======================

minute   0-59
hour   0-23
day of month 1-31
month   1-12
day of week  0-6

crontab -e  //edit crontab job
30 * * * * /root/backup.sh //Run Cron Job Every 30 Minutes
0 4 * * 1-5 /root/backup.sh //run cron job monday to friday
0 4 * * 1,5 /root/backup.sh //run cron job monday and friday only
crontab -l   //list all crontab jobs
crontab -r   //remove all jobs
====================================================