Linux

Linux

3 User Catogories

SuperUser Acount User Acount /home/user Service Acount eg. mysql user only for mysql

Permissions

cat /etc/passwd Has registered user z Format USERNAME : PASSWORD : UID : GID : GECOS : HOMEDIR : SHELL

To create a new user : adduser USERNAME

Creating a group

sudo groupadd devops

cat /etc/

• adduser
• addgroup
• deluser -these all are for interavtive mode and the other is a low level utility where the user shhould gvive alll the necessary information -so the add user can be used interactively while useradd commands can ge userd when automated

  usermod -g groupname username
  

  a user can have one primary and multiple secondary groups For primary group use -g and for seconady use -G

• -G resets all the user secinday groups in order to append the newgroup use -aG

usermod -aG sudo <username>

adding a user to the sudo group

File Permissions and Ownership

Ownership

• Two owners the user and the group

  chown USERNAME:GPOUPNAME FILENAME
  

 sudo chgrp GROUPNAME FILENAME

d rwx-rwx-rwx Owner (u) - Group (g) - Other (o)

Modyfying file permissions

chmod -x api

remove the execcute permisdsion for all the owners

chmod g-w FILENAME

chmod g=rwx FILENAME

RWX R– RW-

chmod 777 FILENAME

Number	Permission Type	Symbol
1	No Permission	–x
2	Execute	-w-
3	Write	-wx
4	Execute + Write	r__
5	Read	r-x
6	Read + Execute	rwx
7	Read +Write	Symbol

Pipeline

using the output of the previous command as the input of the next command

cat /var/log/syslog | less

history | "grep ls -l"

less is a program that displays large content in good manner

Redirection

history > history.txt

redirects the content of the previous commands to a new file

Environment Variables

printenv

Setting a env variable

export DB_USERNAME = dbuser

Deleting an environment variable

unset DB_USERNAME

Persisting an env variable

nano .bashrc

source .bashrc  # used to load the newly added environment variables

Base 64 encoding

echo -n 'username' | base64