If you are a Linux user, you might have seen the following message when you try to install a package or run a command.
$ apt install vim
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?
This is because you don’t have the permission to install a package. In this post, I will explain how to manage permission of files and folders in Linux.
Why do we need permission?
Linux is a multi-user operating system. It means that multiple users can use the same computer at the same time.
Let’s say that you have a single computer in your house and you share it with your family. In some cases, you might want to restrict their access to your valuable files. This is where permission comes in.
Permission is a set of rules that determines who can access a file or folder.
Types of permission
There are three types of permission.
- Read (r)
- Write (w)
- Execute (x)
Permission representation
For example, if the file is read only, it is represented as r--.
If the file is readable and writable, it is represented as rw-.
If the file is readable, writable, and executable, it is represented as rwx.
Permission representation as numbers
Permission can also be represented as numbers.
Each permission is assigned as a digit in binary.
For example, rwx is 111 in binary, which is 7 in decimal.
rw- is 110 in binary, which is 6 in decimal.
r-- is 100 in binary, which is 4 in decimal.
Managing permission
Permission of a file or folder is managed by owner, group, and others.
Checking Owner, Group, and Others
To check the owner, group, and others of a file or folder, use ls -l command.
$ ls -l example.txt
-rw-r--r-- 1 tux parents 0 Jan 9 14:00 example.txt
In this example, the owner is tux, the group is parents.
And the permission of the file is rw-r--r--.
It looks scary, but it is actually simple.
You can divide the permission into three parts.
rw-, r--, and r--.
The first part is the permission of the owner, the second part is the permission of the group, and the third part is the permission of others.
Therefore, this permission can also be represented as 644.
Changing owner
To change the owner of a file or folder, use chown command.
$ chown [owner] [file]
Changing group
To change the group of a file or folder, use chgrp command.
$ chgrp [group] [file]
Changing permission
To change the permission of a file or folder, use chmod command.
$ chmod [permission] [file]
For example, if you want to make a file readable, writable, and executable for the owner, readable for the group, and readable for others, you can use chmod 744 example.txt.
For easier modification, you can use + and - to add or remove permission.
$ chmod u+x example.txt # Add executable permission to the owner
$ chmod g-w example.txt # Remove writable permission from the group
$ chmod o-r example.txt # Remove readable permission from others
Conclusion
In this post, I explained how to manage permission of files and folders in Linux. If you have any questions or suggestions, please leave a comment below.
This post was written for the 2024 Winter Mogakso Activity.
References
Linux Basics for Hackers by OccupyTheWeb, Chapter 5