CHMOD Calculator

CHMOD Configurator

Linux File Permissions Generator
Linux Command
chmod000
———
1. Owner (User)
Read (4)
Write (2)
Execute (1)
2. Group
Read (4)
Write (2)
Execute (1)
3. Public (Others)
Read (4)
Write (2)
Execute (1)
Permission Meaning
Owner:
No access
Group:
No access
Public:
No access

How to use CHMOD & Common Commands

The chmod (change mode) command controls file and directory permissions in Linux and Unix systems. Use the interactive toggles above to generate the exact permission string you need, then copy the command. Below are some standard configurations used in server environments.

Common Permission Scenarios

Unrestricted (777)
chmod 777 directory/
Anyone can read, write, and execute. High security risk.
Web Directories (755)
chmod 755 /var/www/html/
Owner can read/write/execute. Others can read/execute.
Secure Directories (750)
chmod 750 secure_dir/
Owner has full access, group can read/execute, public has no access.
Private Directories (700)
chmod 700 private_dir/
Only the owner can enter, read, or write. Total privacy.
Shared Group Files (664)
chmod 664 project.txt
Owner and group can edit. Public can only read.
Web Files (644)
chmod 644 index.html
Owner can edit. Group and Public can only read.
Secure Configs (640)
chmod 640 wp-config.php
Owner can edit, group can read, public has no access.
Private SSH Keys (600)
chmod 600 id_rsa
Only the owner can read and write. Invisible to everyone else.
Locked Keys (400)
chmod 400 key.pem
Strict read-only access for the owner. Used for AWS PEM keys.
Recursive Update (-R)
chmod -R 755 public_html/
Applies the permissions to the folder and every file inside recursively.

Octal (Numeric) Breakdown

Permissions are mathematically calculated by adding the required access values together for each group (Owner, Group, Public).

  • 4 = Read (r)
  • 2 = Write (w)
  • 1 = Execute (x)
  • 0 = No Permission (-)

A CHMOD Configurator is a tool for creating and understanding Linux and Unix file permissions. It allows users to select permissions for the owner, group, and others and automatically converts those selections into the corresponding numeric (octal) and symbolic chmod notation.

For example, if a file should allow the owner to read, write, and execute it, while the group and everyone else can only read it, the configurator can generate:

chmod 744 filename

The tool is useful because Linux permissions are often represented using compact numeric values such as 755, 644, or 700, which can be difficult to remember without understanding how the permission system works.

What Does a CHMOD Configurator Do?

A CHMOD Configurator typically lets you select three types of users:

  • Owner (user)
  • Group
  • Others

For each category, you can enable or disable:

  • Read (r)
  • Write (w)
  • Execute (x)

The configurator then converts those selections into:

  1. A numeric permission code, such as 755
  2. A symbolic permission string, such as rwxr-xr-x
  3. A complete chmod command, such as:
chmod 755 filename

This makes it easier to create permissions without manually calculating the octal values.

Understanding Linux File Permissions

Linux permissions determine who can access a file or directory and what they are allowed to do with it.

There are three primary permission classes:

Owner

The owner is the user account that owns the file.

Group

The group represents users belonging to the file’s assigned group.

Others

Others refers to users who are neither the file owner nor members of the file’s group.

Each class can have three basic permissions:

PermissionSymbolNumeric value
Readr4
Writew2
Executex1

These values form the foundation of numeric chmod permissions.

How Numeric CHMOD Values Work

The numeric form of chmod usually contains three digits:

755

Each digit corresponds to a permission class:

7   5   5
│   │   │
│   │   └── Others
│   └────── Group
└────────── Owner

Each digit is calculated by adding the values of the enabled permissions.

Read Permission

Read has a value of:

4

Write Permission

Write has a value of:

2

Execute Permission

Execute has a value of:

1

Therefore:

Read + Write + Execute = 4 + 2 + 1 = 7

Similarly:

Read + Write = 4 + 2 = 6

Read + Execute = 4 + 1 = 5

Write + Execute = 2 + 1 = 3

CHMOD Permission Value Table

A CHMOD Configurator commonly uses the following combinations:

Numeric valueSymbolic permissionsMeaning
0---No permissions
1--xExecute only
2-w-Write only
3-wxWrite + execute
4r--Read only
5r-xRead + execute
6rw-Read + write
7rwxRead + write + execute

Each digit in a three-digit CHMOD code uses this same table.

Example: CHMOD 755

Consider:

chmod 755 script.sh

The three digits mean:

  • Owner = 7
  • Group = 5
  • Others = 5

Convert each digit:

7 = 4 + 2 + 1 = rwx

5 = 4 + 1 = r-x

5 = 4 + 1 = r-x

Therefore:

755 = rwxr-xr-x

The owner can read, write, and execute the file.

The group can read and execute it but cannot modify it.

Others can read and execute it but cannot modify it.

Example: CHMOD 644

A common permission configuration for a regular readable file is:

chmod 644 document.txt

The calculation is:

6 = 4 + 2 = rw-

4 = r--

4 = r--

Therefore:

644 = rw-r--r--

The owner can read and modify the file.

The group can read it.

Others can read it.

Example: CHMOD 700

For:

chmod 700 private.sh

The permissions are:

7 = rwx

0 = ---

0 = ---

Therefore:

700 = rwx------

Only the owner has permissions.

How a CHMOD Configurator Calculates the Numeric Code

The conversion process is simple.

Suppose the selected permissions are:

Owner

  • Read ✓
  • Write ✓
  • Execute ✓

Owner value:

4 + 2 + 1 = 7

Group

  • Read ✓
  • Write ✗
  • Execute ✓

Group value:

4 + 1 = 5

Others

  • Read ✓
  • Write ✗
  • Execute ✗

Others value:

4

The resulting numeric permission is:

754

The symbolic representation is:

rwxr-xr--

The corresponding command would be:

chmod 754 filename

Symbolic CHMOD Notation

Permissions can also be written symbolically.

For example:

rwxr-xr-x

The string contains three groups:

rwx   r-x   r-x
│     │     │
│     │     └── Others
│     └──────── Group
└────────────── Owner

The first character of a complete ls -l permission display may represent the file type.

For example:

-rwxr-xr-x

Here:

  • - indicates a regular file
  • rwx = owner permissions
  • r-x = group permissions
  • r-x = others permissions

A directory commonly begins with d, such as:

drwxr-xr-x

The d indicates a directory rather than a regular file.

Symbolic CHMOD Commands

The CHMOD Configurator may also help generate symbolic commands.

For example:

chmod u+x script.sh

means to add execute permission for the owner.

The symbolic user categories are commonly:

SymbolMeaning
uUser/owner
gGroup
oOthers
aAll three classes

Operators include:

OperatorFunction
+Add permission
-Remove permission
=Set permissions exactly

For example:

chmod g+w file.txt

adds write permission for the group.

Another example:

chmod o-r file.txt

removes read permission from others.

CHMOD Configurator: Numeric to Symbolic Conversion

A configurator can also work in the opposite direction.

Suppose the input is:

751

Convert each digit:

7 = rwx

5 = r-x

1 = --x

Therefore:

751 = rwxr-x--x

This makes it easier to understand what an unfamiliar numeric permission actually allows.

Special Permissions

Some CHMOD configurators also support special permission bits beyond the standard read, write, and execute permissions.

These include:

  • Set User ID (SUID)
  • Set Group ID (SGID)
  • Sticky bit

They are commonly represented using an additional leading numeric digit.

The special permission values are:

Special permissionNumeric value
SUID4
SGID2
Sticky bit1

For example, a four-digit mode can contain:

4755

The leading 4 represents SUID, while 755 represents the standard owner/group/others permissions.

Because special permissions can affect how programs and directories operate, they should be used deliberately rather than added simply to make a permission string look correct.

CHMOD Permissions for Directories

Permissions have somewhat different practical effects on directories.

For a directory:

  • Read generally allows listing directory entries.
  • Write generally allows creating, deleting, or renaming entries, subject to other permissions and filesystem rules.
  • Execute generally allows accessing/traversing the directory.

For example:

chmod 755 myfolder

produces:

drwxr-xr-x

The owner has full permissions, while group and others can read/list and traverse the directory but cannot normally create or delete entries within it.

Common CHMOD Configurations

Some frequently encountered configurations include:

ModeSymbolic formGeneral use
600rw-------Private file
644rw-r--r--Regular readable file
700rwx------Private executable/directory
755rwxr-xr-xExecutable file or commonly accessible directory
775rwxrwxr-xGroup-writable file or directory
777rwxrwxrwxFull permissions for everyone

These are examples, not universal recommendations. The appropriate permissions depend on the application’s requirements and security model.

Important Security Considerations

File permissions directly affect system security.

Giving unnecessary permissions can allow users or processes to modify, execute, or access files that should be restricted.

For example:

chmod 777 file.txt

grants read, write, and execute permissions to the owner, group, and others. This is substantially broader access than:

chmod 644 file.txt

which allows the owner to read and write while giving group and others read-only access.

The correct permission depends on the file, application, users, and operating environment. A configurator can accurately calculate the requested permission mode, but it cannot determine the appropriate security policy for every system.

Frequently Asked Questions

What does CHMOD mean?

chmod stands for change mode. It is a Unix/Linux command used to change file and directory permission modes.

What does 755 mean in CHMOD?

755 means:

rwxr-xr-x

The owner has read, write, and execute permissions. The group and others have read and execute permissions.

What does 644 mean?

644 means:

rw-r--r--

The owner can read and write, while group and others can read.

What is the numeric value of read permission?

Read is represented by 4.

What is the numeric value of write permission?

Write is represented by 2.

What is the numeric value of execute permission?

Execute is represented by 1.

Why is 7 equal to rwx?

Because:

4 + 2 + 1 = 7

Therefore, 7 represents read, write, and execute.

Can a CHMOD Configurator generate commands?

Yes. A configurator can combine the selected permissions into a command such as:

chmod 755 filename

Does CHMOD work only on files?

No. chmod can be used with both files and directories. The practical meaning of permissions, particularly execute permission, differs between regular files and directories.