# Basic of Linux # Linux -2 Understanding Linux file permissions (how to find them, read them, and change them) is an important part of maintaining and securing your systems. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1679465483861/3502bde1-b96e-4c9b-9545-fa79db565822.png align="center") **Change the access permissions of a file** There are three options for **permission groups** available to you in Linux. These are * ***owners***: these permissions will only apply to owners and will not affect other groups. * ***groups***: you can assign a group of users specific permissions, which will only impact users within the group. * ***all users***: these permissions will apply to all users, and as a result, they present the greatest security risk and should be assigned with caution.

u

user

g

group

o

others

a

all

**Linux file permission** falls into three categories: * ***Read (r)***: allow users to open and read the file only. Users can’t modify the file. * ***Write (w)***: the user can modify (edit, delete) the file and save it. * ***Execute (x)***: allows the user to run an executable script

r

Read

w

Write

x

Execute

-

No permission

*The first column here indicates the* ***permission*** *for the particular file/folder.* *If the permission starts with “* ***—*** *“, it indicates that it is a* ***file***\*.\* *Whereas, permissions starting with “****d****“ indicate it is a* ***directory***\*.\* *Then, every three characters in the permission column indicate the* ***permissions*** *set for various owners in the order of* ***owner, group*** *and* ***others*** *respectively.* ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1679464744835/e7f7659b-4534-4209-b3bd-eaf5a6df317b.png align="center") ***Changing file/directory permissions in Linux Using ‘chmod’*** *command* *syntax:* ***chmod permissions filename*** *There are two ways to change the permission:* 1. *Absolute(numeric) mode* 2. *Symbolic mode* # ***Absolute mode*** *In this mode, file* ***permissions*** *are not represented as* ***characters*** *but as a* ***three-digit octal number***\*.\* * *0 = No Permission* * *1 = Execute* * *2 = Write* * *4 = Read* *Basically, you add up the numbers depending on the level of permission you want to give.*

Number

Permission

Symbol

0

No permission

---

1

Execute

--x

2

Write

-w-

3

Execute + Write

-wx

4

Read

r--

5

Read + Execute

r-x

6

Read + Write

rw-

7

Read + Write + Execute

rwx

*Refer to a simple example here…* ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1679465040166/0556c109-2625-414c-8f08-74677395b5dd.png align="center") # ***Symbolic mode***

Operator 

Description

+

Adds permission to a file/directory

-

Removes the permission

=

Sets the permission and overrides the permissions set earlier

In this mode, we can simply change the permission by **chmod (user)(operator)(permission) \[filename\]** Refer to this simple example… ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1679465329229/cca9a466-50f2-4eb1-8840-3c6ea18b61d8.png align="center") It can be well understood that ‘o-w’ here indicates *removing* the write permission from *other* user groups. chmod u=rwx,g=rwx,o=rwx \[file\_name\] chmod 644 test.txt chown \[user\_name\] \[file\_name\] chgrp \[group\_name\] \[file\_name\] Thank you for reading !!