Understand Read, Write and Execute

The letters r, w and x look the same in every triplet, but their meaning depends on the entry. For a regular file they concern reading bytes, modifying bytes and executing an appropriate program. For a directory they concern listing names, changing entries and searching through paths.

That directory distinction explains several surprises. You can know a filename without being allowed to list the directory, and deleting a file is not just a question about writing the file's contents. Let's examine the directory side using a classroom folder.

Prepare the example

Use a new practice folder. The block creates a classroom directory and sets ordinary mode 750 so its triplets are predictable. We are inspecting meanings here, not changing a production report folder's access. Owner, group and others still identify separate classes.

Bash · Linux terminal

mkdir classroom
chmod 750 classroom
ls -ld classroom

Expected behavior; machine-dependent details

The mode begins drwxr-x---.

For the directory mode 750, the owner gets rwx, the group gets r-x and others get no ordinary bits. Directory read permits listing names, search/execute permits traversing to known entries, and write participates in creating, removing or renaming entries when the other required checks allow it.

Now contrast changing a report's bytes with deleting its name from the parent directory. Those operations act on different objects. A read-only regular file can still be removable by someone with the required parent-directory permissions, subject to sticky, ACL and other rules. Do not use the word 'write' without naming what is being written.

The letters r, w and x are the building blocks of traditional Linux permissions. Their meaning depends partly on whether the object is a regular file or a directory.

What do these symbols mean?

• r (read) – Allows viewing the contents of a file or listing the contents of a directory.
• w (write) – Allows modifying a file or adding/removing files in a directory.
• x (execute) – Allows running a file (like a script), or entering a directory.

Let’s see permissions in action

We’ll use the ls -l command to list files along with their permissions.

ls -l

-rwxr-xr--  1 user user  2048 Jul  1 10:00 hello.sh

This output shows a file named hello.sh. Let’s break down the leftmost part: -rwxr-xr--

Permission breakdown

Try this example yourself

Create a file and check its default permissions:

touch myfile.txt
ls -l myfile.txt

-rw-r--r-- 1 user user 0 Jul  2 11:30 myfile.txt

This means:

• User can read and write the file
• Group can only read
• Others can only read

What about directories?

Directory permissions behave slightly differently:

• r – Can list directory contents
• w – Can create/delete files in the directory
• x – Can enter ("cd into") the directory

Let’s check a directory’s permissions:

mkdir testdir
ls -ld testdir

drwxr-xr-x 2 user user 4096 Jul  2 11:35 testdir

This means:

• User can list, write, and enter the directory
• Group and others can read and enter, but not modify

Quick tip: Use chmod to change permissions

For example, to add execute permission for everyone on a file:

chmod +x hello.sh
ls -l hello.sh

-rwxr-xr-x 1 user user 2048 Jul  2 11:40 hello.sh

Now everyone can execute the script!

Interpret r, w and x for files and directories

Permissions are crucial to keeping your Linux system secure and organized. Knowing what r, w, and x mean will help you control access to your files and directories with confidence.

In upcoming lessons, we'll explore changing permissions using chmod, chown, and symbolic vs numeric modes. Stay tuned!

Think of the report contents and its name in a directory as two different objects you can affect. Writing a new mark changes the file bytes. Removing the report name changes the parent directory entries. That explains why a read-only report can still be removable when the actor has the required write and search access to its parent.

A sticky directory adds restrictions on who can remove or rename entries, and ACLs or other system policy can add further checks. A removal tool may also ask for confirmation on a read-only file; that prompt is not the same as a kernel rule requiring file write access. When predicting the result, name the operation first, then inspect the object whose permissions govern it.

Your task: Which directory permission permits traversal to a known entry?

Use a new practice folder. The block creates a classroom directory and sets ordinary mode 750 so its triplets are predictable. We are inspecting meanings here, not changing a production report folder's access. Owner, group and others still identify separate classes.

Bash · complete example for this question

mkdir classroom
chmod 750 classroom
ls -ld classroom

Expected behavior; machine-dependent details

The mode begins drwxr-x---.

Worked answer

Execute/search.

Directory execute/search is the bit relevant to traversal of a known entry. Directory read alone is about listing names. File write is about changing the file's bytes, so it does not replace the required traversal access on directories in the path.

Interpret each bit for the entry type before predicting an operation. Reading names, traversing a path, editing bytes and deleting an entry are different tasks. Identify the file or directory involved in each task, then consider the relevant bits and additional access rules.