Linux File Permissions

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In linux you will learn about file permission it's will let users access to certain file on the linux. We used chmod command to change the file permissions on linux. There are two type of chmod which is symbolic and numeric. The symbolic method is good for changing one set of permissions at a time while numeric you required to know about each octal value to give certain permission for example 777 is give User : read, write, execute; group : read, write, execute; others : read, write, execute

Frist thing you need to know about role flag on file. its user owner, group owner and other.
user owner : is the user who created the file
group owener : is the group name which user who created the file belong to
other : other user not in the system

let's we check :

sysadmin@localhost:~/perm$ touch andre.txt

sysadmin@localhost:~/perm$ ls -l

total 0

-rw-rw-r-- 1 sysadmin sysadmin 0 May  9 06:22 andre.txt

- The red one is for users owner

- The blue one is for group owner

- The green one is others

- The higlighted yelow is user owner
- The higlighted green is group owner

Now you already know to flag on file, we can continue to the next material.

I already mention in the begining that we have two method which is symbolic and numeric

Symbolic method :
First you need to understand the symbol below for object
Symbol Group
u user owner
g group owner
o others
a all (user owner, group owner, and others)

Second you need to understand the symbol below for permission

Symbol Permission

r read

w write

x execute

Third is for operator

Symbol Operation

+ add the permission, if necessary

= specify the exact permission

- remove the permission, if necessary

Example to use symbolic method

We already create the file called andre.txt in the begining

sysadmin@localhost:~/perm$ ls -l

total 0

-rw-rw-r-- 1 sysadmin sysadmin 0 May  9 06:22 andre.txt

Now we try to give them execute permission

sysadmin@localhost:~/perm$ chmod u+x andre.txt 

sysadmin@localhost:~/perm$ ls -l 

total 0

-rwxrw-r-- 1 sysadmin sysadmin 0 May  9 06:22 andre.txt

Now the file permission is changed on the user segment.

We try to remove group write permission

sysadmin@localhost:~$ chmod g-w andre.txt

sysadmin@localhost:~$ ls -l andre.txt

-rwxr--r-- 1 sysadmin sysadmin 0 Mar 21 18:10 andre.txt

One more example we try to give others exact read permission, remove write from group and add executeable to user

sysadmin@localhost:~$ chmod o=wr,g+w,u-x andre.txt

sysadmin@localhost:~$ ls -l andre.txt

-rw-rw-rw- 1 sysadmin sysadmin 0 May  9 06:22 andre.txt

Numeric method :

The other method beside symbolic is numeric rather than using alpabet the numeric method using octal number to define permission on the linux. It's look wierd at the first time but if you know the concept it's also easy to use.

Fitst thing you have to understand well about the concept below
Octal Value Permission
4 read
2 write
1 execute
0 none

xample numeric method

I try to put

sysadmin@localhost:~/perm$ chmod 444 andre.txt

sysadmin@localhost:~/perm$ ls -l

total 0

-r--r--r-- 1 sysadmin sysadmin 0 May  9 08:46 andre.txt

Another example, now I will make user : read, write, execute; group: read,write; other:read

sysadmin@localhost:~/perm$ chmod 764 andre.txt

sysadmin@localhost:~/perm$ ls -l

total 0 

-rwxrw-r-- 1 sysadmin sysadmin 0 May  9 08:46 andre.txt

How's do you think about? it's great right?

Both symbolic and numeric is just flavour and it's will result the same :)

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