Linux File Permissions

Basic File Permissions

Linux systems in general break file permissions into three basic types:

• Read
• Write
• Execute

These basic types tie into the ownership of the file. The owners are broken down into three groups as well:

• Owner
• Group
• Other

These permissions and ownerships are represented as a three digit number. Each digit can have a value of 0-7 (inclusive). first digit represents owner permissions, the second digit represents group permissions, and the last digit is for others. There is a number associated with each permission where read has a value of 4, write has a value of 2, and execute has a value of 1.

When we look at the binary values for these permissions it all makes sense:

Read:    (4)d = (100)b
Write:   (2)d = (010)b
Execute: (1)d = (001)b
----------------------
All:     (7)d = (111)b

because of this design we can easily find/set permissions for any file in linux.

For example a file that has all permissions for Owner, but no permissions for group or others will have a permission of 700.

Changing permissions on a file in Linux

To change the permissions of a file we use a utility called chmod. chmod stands for Change Mode. This is a utility that is shipped with many linux distributions. Since chmod is changing permissions on a file (writing new permissions) then you need to have write access to the file that you are trying to change.

so the code looks like something like this: sudo chmod 777 file_name

Changing ownership of a file in linux

To change the ownership of a file we use a utility called chown which stands for change owner the syntax for this is as follows:
sudo chown user:user_group file_name

If you have any questions or there is something incorrect here please let me know and I will fix it.