Linux Commands

To list all files and folders

ls -al /tmp

ls = command
-l = option
-a = display hidden files
/temp - argument

To create a directory

mkdir directory_name

To remove a File

rm file_name

To delete a directory

rm -r directory_name

-r - recursive

To remove empty directory

rmdir directory_name

To Enter a directory

cd directory_name

To know who loggedin into you system in the past

last

To know your username

whoami

Prompt

[student@localhost ~]$

student = username
localhost = computer name
~ = location
$ = loggedin user is a non root user

# = loggedin user is root

To know who is looged in into the server

who

To know what the user is doing

To know the name of your server

hostname

To know the kernel version of your system

username -r

-r - revision number

To know the date/time in the serve

date

To know the ip address of your server

ip a

To check internet connectivity

ping google.com

To see all the command you typed

history

To display present working directory

pwd

To move to root directory

cd / or cd ~

To switch user

su ${username}

To switch to root user

su - root // This is not a good practice

To switch to root

sudo su - root

su means switch user

To logout

ctrl+d or logout or exit

To add a new user

sudo useradd ${username}

Non-root users have limited priviledges - run limited command

To add a user

sudo useradd ${username}

when using sudo everything is logged.

To give a user password

sudo passwd ${username}

To remove everything inside a directory

rm -rf \* directory_name

To find a word in a file

grep ${search_word} ${file_path}

To get the line number where the word appeared

grep -n {search_word} ${file_path}

-i = ignore the case
-n = show the line number
-o = only occurance
-v = ignore the word

To copy file from one location to another

cp ${source} ${destination}

To copy all the items of a directory to another location

cp -rv ${source} to ${destination}

-r = recursive
-v = variable

To copy all the items of a directory to another location with the folder

mv ${source} ${destination}

To create nested directory

mkdir -p directory/directory

-p = create parent directory

To create alias

alias ld='ls -al'

To see all alias commands

alias

VI Editor
VI - Visual Instrument
VIM - visual instrument improved

- insert mode = to make changes (a, i insert) <br />
- command mode = to save the file, close the file, show line number etc.
  To exist insert mode
  esc key
  To Save file
  :w
  To quit
  :q
  To save and quit
  :wq
  To undo
  press u
  To delete a line
  press d twice
  To display the line number
  :se nu
  To exit without saving
  :q!

To know the name of your operating system

cat /etc/os-release

To find the current version

uname -r

-r = revision

To see the user

id ${username}

User pasword and groups are stored in etc folder
user
-> passwd (/etc/)
-> group (/etc/)

To check user details

grep ${username} /etc/passwd

Output

student:x:1000:1000:tudent:/home/student:/bin/bash
1st -username
2nd - passwd
3rd - uid
4th - gid
5th - command
6th - location of home directory
7th - name of the shell assigned to the user

To Know the user group

grep user2 /etc/group

Output

wheel::10:student

1st - name of the group
2nd - password
3rd - group id
4th - users that are part of the group

To Know the user group

grep user2 /etc/shadow

Output

chuks:$8EuYko8Y9dWhj0:1906:1:99999:7:::

1 - username
2 - password hash (99999 - never expire)
3 - last pass change date details
4 - min days between password change
5 - pass expiration in days
6 - warning days
7 - password inactive date
8 - account inactive date

How to change the detail above

list all details

chage -l ${username}

How to change the detail above

chage ${username} and follow the prompt

To change the password of the root user

sudo su - root

ldap - lightweight Directory Access Protocol

To see your type of user

which useradd

To add a user

sudo su - root
useradd ${username}

To set user password

sudo passwd ${username}

To add a user to a group

usermod -G group1,group1 -u 2500 -c "comment" -s /usr/bin/sh ${username}

-c = modify comments
-g = modify primary group
-G = modify secondary group
-a = retain all secondary group
-u = uid
-s = shell
-d = /${username}

How to create a group

groupadd ${groupname}

To verify

grep ${groupname} /etc/group

How to delete a group

groupdel ${groupname}

To Delete a user

userdel -r ${username}

To open sudo file

visudo

Why Linux is secure

file level security - permission(basic, ACL, Special)
SElinux - what is happening inside OS
firewall - filters network traffic

Things attached to a file

who is the owner
who is the group owner
what are the permission on the file

Permissions in linux

read - r = 4
write - w = 2
execute - x = 1
read-write - rw = 6
read-execute - rx = 5
read-write-execute - rwx = 7
no permission - 0
owner - u
group - g
others - o
all - a

To change user permission

owner - oshabz - rw -rw
group - oshabz - rw - r
others - r - r

To display information about a file

stat ${filename}

To change the user's permission

sudo chmode 660 ${filename}

To change the group owner of a file

chown ${owner_name}:${group_name} ${file_name};

Chaning and Piping command

use semicolon to chain commands

cd new_folder; npm run start; code .

Piping This takes output from left and use it as input on the right

ls -l | grep rpc

grep bash /etc/passwd | wc -l

how to get number of character and words

wc /etc/passwd

To print out data in a file

ls -l abc >out.txt 2> error.log

single greater than(>) means replace the previous text

grep bash /etc/passwd | wc -l > out.txt

Double greater than(>) means append

grep bash /etc/passwd | wc -l >> out.txt

To save the error in error log

grep bash /etc/passwd | wc -l >> out.txt 2>> error.log

To Check the CPU

lscpu

To check RAM

free -h

To check your computer serial number

dmidecode -t1

To know the disk status

df -h

To check the hard disk and ram in your system

lsblk

To mount a device

sudo su - root

To mount drive

mount ${source} ${destination}

Ignore all lines that contains tmpfs

df -h | grep -v tmpfs

To check disc usage

du -sh \

To check disk in human readable form

df -h

Type of users

Root(Admin)
Non-root
system/application

System user cn not login (because they dont have login shell. They are created for support of application)

To check the number of users that can login

grep bash /etc/passwd | wc -l

To check the users who cant login

grep nologin /etc/passwd | wc -l

Find is used to find and perform actions while locate can only output the search

To find and perform an action

find ${start_search_from} ${options} ${what_to_find} ${what_action_to_take}

To search for a file/diectory

find / -name type  -d $(file_name.ext)

To search a file with permission

find /home type f -perm 644

To change the permission of a file with the file command

find / -type f -print -perm 666 -exec chmod 644 {} \;

To locate a file

First update database by using the following command

updatedb

To locate a file

locate ${file_name}

To get date and time details

timedatectl

To create multiple files

touch filename{1..10}

Inodes are used to store file meta data like filename, file size etc

To get inode folders

df -hi

Link is the same thing as shortcut

Wildcard

To delete file starting with a text

rm -f ${filename_starting_with}*

To copy files that start with a text

cp ${filename_starting_with}* ${location}

To delete all files in a folder

rm -f *

To display a file with a single character in filename

ls -l ?

To display filename starting with a range of character

ls -l [ax]*

This mean list all file name that start with a and also file name that start with x

To create a range of files

touch filename{1..10}

timilehin2000/linux-commands

Linux Commands

How to change the detail above

Chaning and Piping command