Permission denied

Every file or directory in Linux has an owner and a set of permissions. When accessing them, the operating system checks these permissions. If the user has sufficient permissions, access will be granted. Otherwise, an error Permission denied will be displayed.

Check the directory owner

To understand who owns a file or directory, simply run the following command:

ls -l

total 0
-rwx------ 1 testuser testuser 0 Sep 27 10:16 test

Let’s take a closer look at the output. We work under a user with the name usergpu. There is one file in our home directory named test. The permissions -rwx------ mean that only the owner can read, write, and execute this file. Read more about Linux permissions.

Other users or groups don't have access to this file, except for the superuser (root). Finally, we see information about the owner (username testuser) and owner’s group (the group name is the same testuser).

If we try to do anything with this file on behalf of the user without permission, the system shows an error message:

cat test

cat: test: Permission denied

Fix the permissions

Log in as the owner

If you have the owner’s credentials, you can log in and perform any actions with this file:

cat test

Hello, LeaderGPU!

Change the owner

You can get access to the file by changing its owner. This action can be executed on behalf of a user with root privileges (for example, using sudo command):

sudo chown usergpu test

And test:

cat test

Hello, LeaderGPU!

Use superuser privileges

The sudo command is the most powerful:

sudo cat test

Hello, LeaderGPU!