chmod command

Using the chmod Command on Ubuntu

Sagar Sharma
Sagar Sharma

Table of Contents

As Linux is built to have multiple users at the same time, you are given multiple file permissions for reading, writing, and execution.

If you are using Linux for while or just getting started, you will have to deal with file permissions a lot. You can change the file permissions with the chmod command.

In this article, I'll share a few examples of using the chmod command for changing the file permissions.

Basics of File permissions

Before I jump to the chmod command part, it is necessary for you to know the file permissions in Linux.

To know permission for any file, all you have to do is append the filename to the ls command with the -lh flag:

ls -lh filename
check file permissions with the ls command on linux

Doesn't tell much. Right?

Well, here's a simple illustration to make things easy to digest:

To learn more about file permissions, I would highly recommend the other guide of ours going in depth of file permissions:

Linux File Permissions and Ownership Explained with Examples
Linux file permissions explained in simpler terms. Also learn how to change the file permissions and ownership in Linux in this detailed beginner’s guide.

Now, let's jump to the chmod command examples.

Chmod command examples

To execute the chmod command, you will need to follow the given command syntax:

chmod [options] filename

Where in the options, you are supposed to use numbers as flags to change the permissions:

Number Permission Description
o --- No permissions
1 --x Execute only
2 -w- Write only
3 (i.e. 2+1) -wx Write and execute only
4 r-- Read-only
5 (i.e. 4+1) r-x Read and execute only
6 (i.e. 4+2) rw- Read and write only
7 (i.e. 4+2+1) rwx Read, write and execute

But if you want to use the chmod command in symbolic form, you can also do that by following the syntax:

chmod [Options] [Operator] Filename

In symbolic form, you have 4 options to choose the permissions:

  • u indicates user owner
  • g indicates the group owner
  • o indicates others
  • a is used for all (user, group, and others)

For [Operator], it accepts the following:

  • + is used to add specified permissions
  • - is used to remove specified permissions
  • = is used to define exact permissions for another user

Now, let's have a look at examples.

1. Set read by owner only: chmod 400

If you want your file with read-only permission for owners only and zero permissions for others, you can use chmod 400 as shown:

chmod 400 filename
read only permissions using chmod command

The same can be done with the symbolic mode:

chmod u=r testfile
read only permissions for owner only using chmod command in symbolic mode

2. Allow execution permissions to everyone: chmod 111

If you want to allow everyone to execute a specific file, it can easily be done using the chmod 111:

chmod 111 testfile
Allow execution permissions to everyone

And if you prefer symbolic form, here you have it:

chmod a=x testfile
Allow execution permissions to everyone using symbolic form

3. Write only by the owner: chmod 200

If you want the write permissions restricted to the owner, you can use chmod 200:

chmod 200 testfile
set write only permission for owner only

And if you want to do the same in symbolic mode, use the following:

chmod u=w testfile
write only permission for owner using the chmod command in symbolic mode

4. Change permissions recursively

If you want to have the same permissions for the whole directory, you can apply the same permissions using -R flag and it will have a recursive effect:

chmod -R [permission] Target_Directory

So let's say I want to allow every user to read, write and execute the contents of LU directory, I will be using the following:

chmod -R 777 LU
change permissions recursively using the chmod command on ubuntu

And if you wish to do the same using symbolic mode:

chmod -R a=rwx Target_Directory
change file permissions recursively using the chmod command in symbolic mode

5. All rights to owners and others are limited to read-only: chmod 744

If you want the file owner to have every permission and want to limit others to read-only, use chmod 744:

chmod 744 testfile
All rights to owners and others are limited to read-only

For symbolic mode:

In times when you want to have different permission for user owner, group owner, and others, you are required to add permissions for them separately.

So if I want to have all rights for the owner and others should be limited to read-only, I will use the chmod command in the following way:

chmod u=rwx,g=r,o=r testfile
All rights to owners and others are limited to read-only using chmod command in symbolic mode

Pretty straightforward. Right?

But what about changing the file ownership?

That was all about changing file permissions. As I discussed in the betginning of this article, there is also the ownership. You can change file ownership with the chown command.

How to Change File Ownership in Ubuntu
Here’s how to change the ownership of files and folders in Ubuntu command line.

I hope you will find this guide helpful. If you face any issue while command execution or want to suggest what should I cover next, let me know in the comments.

Sagar Sharma

Sagar Sharma

A software engineer who loves to tinker with hardware till it gets crashed. While reviving my crashed system, you can find me reading literature, manga, or watering my plants.