File and Directory Permissions

Permisssions¶

It is possible for some OSs and upload mechanisms to create directories in your PythonAnywhere storage that you cannot use. This is generally because the permissions on those files or directories are set incorrectly. It is relatively easy to tell when this has happened and to fix it. In this article, we will cover how to identify the problem and how to fix it.

The first way that you are likely to notice the issue is when trying to do file operations on a file or in a specific directory or group of directories and you get a Permission denied error of some sort.

Introduction to file and directory permissions¶

Linux uses a permission system to control who can read, write, or execute files and directories. Every file and directory has three sets of permissions:

User (u): The owner of the file
Group (g): Members of the file's group
Other (o): Everyone else on the system

Each set can have three types of permissions:

Read (r): View the contents of a file or list the contents of a directory
Write (w): Modify or delete a file, or add/remove files in a directory
Execute (x): Run a file as a program, or access files inside a directory

When you run ls -l, you'll see permissions displayed as a string like -rwxr-xr--. The first character indicates the type (- for file, d for directory), followed by three groups of three characters showing user, group, and other permissions respectively.

For example:

-rw-r--r-- 1 username registered_users 1234 Sep 2 15:17 myfile.py

This shows a file where the user can read and write (rw-), the group can read (r--), and others can read (r--).

When permissions are set incorrectly, you'll get Permission denied errors when trying to access files or directories. The following sections show how to identify and fix these issues.

File permissions¶

As an exmaple, I have created a file called test_file and purposefully broken its permissions:

$ cat test_file
cat: test_file: Permission denied

We can check the permissions on the file like this:

$ ls -l test_file
-------r-- 2 username registered_users 4096 Sep  2 15:17 test_file

This file has no permissions for user and group, but does have read for root. There may be other patterns in the first column that show different permissions.

Whatever the permissions on the file are, you can fix them with the chmod program in a Bash console:

chmod u+rw test_file

You can also mark a file as executable if you would like to run it directly from a Bash console or in a Task.

chmod u+rwx test_file

Note: These are simple examples and you can be more specific, but this help page will not cover the other uses of chmod.

Directory permissions¶

As an example, I have created a directory called test_dir and purposefully broken its permissions:

$ cat test_dir/some_file
cat: test_dir/some_file: Permission denied

We can check the permissions on the directory like this:

$ ls -ld test_dir
drw-rw-r-- 2 username registered_users 4096 Sep  2 15:17 test_dir

In the above output, we can see that the directory does not have execute permissions.

If you have a directory that does not have execute permissions, it is easy to add them like this:

$ chmod +x test_dir

Now, when we check the permissions on the directory, we can see that it has execute permissions:

$ ls -ld test_dir
drwxrwxr-x 2 glenn registered_users 4096 Sep  2 15:17 test_dir

If you have nested directories (like dir1/dir2/dir3), you will need to set the permissions at each level from the top level directory down:

$ chmod +x dir1
$ chmod +x dir1/dir2
$ chmod +x dir1/dir2/dir3