# Linux commands: chmod

> Learn how the Linux chmod command changes file permissions for the owner, group, and others, using symbolic letters like u+x or numeric modes like 644.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-09-23 | Topics: [CLI](https://flaviocopes.com/tags/cli/) | Canonical: https://flaviocopes.com/linux-command-chmod/

Every file in the Linux / macOS Operating Systems (and UNIX systems in general) has 3 permissions: Read, write, execute.

Go into a folder, and run the `ls -al` command.

![Terminal output of ls -al command showing file permissions, ownership, sizes, and names in a directory listing](https://flaviocopes.com/images/linux-command-chmod/Screen_Shot_2020-09-03_at_18.49.22.png)

The weird strings you see on each file line, like `drwxr-xr-x`, define the permissions of the file or folder.

Let's dissect it.

The first letter indicates the type of file:

- `-` means it's a normal file
- `d` means it's a directory
- `l` means it's a link

Then you have 3 sets of values:

- The first set represents the permissions of the **owner** of the file
- The second set represents the permissions of the members of the **group** the file is associated to
- The third set represents the permissions of the **everyone else**

Those sets are composed by 3 values. `rwx` means that specific _persona_ has read, write and execution access. Anything that is removed is swapped with a `-`, which lets you form various combinations of values and relative permissions: `rw-`, `r--`, `r-x`, and so on.

You can change the permissions given to a file using the `chmod` command.

`chmod` can be used in 2 ways. The first is using symbolic arguments, the second is using numeric arguments. Let's start with symbols first, which is more intuitive.

You type `chmod` followed by a space, and a letter:

- `a` stands for _all_
- `u` stands for _user_
- `g` stands for _group_
- `o` stands for _others_

Then you type either `+` or `-` to add a permission, or to remove it. Then you enter one or more permissions symbols (`r`, `w`, `x`).

All followed by the file or folder name.

Here are some examples:

```bash
chmod a+r filename #everyone can now read
chmod a+rw filename #everyone can now read and write
chmod o-rwx filename #others (not the owner, not in the same group of the file) cannot read, write or execute the file
```

You can apply the same permissions to multiple personas by adding multiple letters before the `+`/`-`:

```bash
chmod og-r filename #other and group can't read any more
```

In case you are editing a folder, you can apply the permissions to every file contained in that folder using the `-r` (recursive) flag.

Numeric arguments are faster but I find them hard to remember when you are not using them day to day. You use a digit that represents the permissions of the persona. This number value can be a maximum of 7, and it's calculated in this way:

- `1` if has execution permission
- `2` if has write permission
- `4` if has read permission

This gives us 4 combinations:

- `0` no permissions
- `1` can execute
- `2` can write
- `3` can write, execute
- `4` can read
- `5` can read, execute
- `6` can read, write
- `7` can read, write and execute

We use them in pairs of 3, to set the permissions of all the 3 groups altogether:

```bash
chmod 777 filename
chmod 755 filename
chmod 644 filename
```

If you don't want to do the math, I built a free [chmod calculator](https://flaviocopes.com/tools/chmod-calculator/) that converts between the `rwx` notation, octal numbers, and `ls -l` output.

> The `chmod` command works on Linux, macOS, WSL, and anywhere you have a UNIX environment