1. Numeric chmod calculator
Enter a three-digit or four-digit octal permission value. Each digit represents a combination of read, write and execute permissions.
| Permission | Owner | Group | Others |
|---|---|---|---|
| Read (4) | r | r | r |
| Write (2) | w | - | - |
| Execute (1) | x | x | x |
2. Build custom permissions
Select the permissions you want to grant to the file owner, group members and other users.
Special permissions
Run an executable with the file owner's effective user ID, subject to system rules.
On executable files, affects the effective group ID. On directories, can influence group inheritance.
On shared directories, restricts who can remove or rename entries.
u=rwx,g=rx,o=rx
3. Generate chmod command
Generate a command using the numeric or symbolic permission value. Enter the target file or directory.
Applies the permissions to the directory and its contents.
Displays information about permission changes.
chmod 755 -- 'example.txt'
4. Common chmod permission presets
Select a preset to load its permission value into the numeric calculator.
chmod 777 as a general fix for
permission problems. It grants read, write and execute access
to everyone. Use the narrowest permissions that your application
actually requires.
5. Understanding chmod numbers
Each basic permission has a numeric value. Add the values together to calculate the digit for each user category.
| Permission | Letter | Value | Meaning |
|---|---|---|---|
| Read | r | 4 | View file contents or list directory entries. |
| Write | w | 2 | Modify a file or directory entries. |
| Execute | x | 1 | Execute a file or search/traverse a directory. |
| No permission | - | 0 | No corresponding permission. |
How is 755 calculated?
The first digit is for the owner, the second for the group, and the third for others.
4 + 2 + 1 = read + write + execute (rwx)
4 + 1 = read + execute (r-x)
4 + 1 = read + execute (r-x)
Therefore, chmod 755 example sets the basic
permissions to rwxr-xr-x.
Special permission digits
| Value | Special permission | Letter |
|---|---|---|
| 4 | Set-user-ID | s |
| 2 | Set-group-ID | s |
| 1 | Sticky bit | t |
A four-digit mode uses the first digit for special permissions.
For example, 4755 combines SetUID with basic
permissions of 755.
Frequently asked questions
What does chmod mean?
Chmod means change mode. It is a Unix and Linux command used to modify file and directory permission bits.
What does chmod 755 mean?
It gives the owner read, write and execute permissions. Group members and other users receive read and execute permissions, but not write permission.
What does chmod 644 mean?
The owner can read and write the file. Group members and
other users can read it but cannot write to it.
Its symbolic representation is rw-r--r--.
What does chmod 777 mean?
It grants read, write and execute permissions to the owner, group and everyone else. This is generally unsafe for files and directories exposed to multiple users.
What is the difference between numeric and symbolic chmod?
Numeric chmod uses octal values such as 755.
Symbolic chmod uses letters and operators such as
u+x, g-w, or
u=rwx,go=rx. Both methods modify permission bits.
What does chmod -R do?
The -R option applies permission changes recursively
to a directory and its contents. Use it carefully because
files and subdirectories may need different permissions.
Does this calculator change my server permissions?
No. This tool only calculates permission values and generates commands. You must run the generated command yourself in an appropriate terminal or server environment.
Can I use chmod on Windows?
The chmod command is primarily used in Unix-like environments. Windows users may encounter it in environments such as WSL, Git Bash, or other Unix-compatible shells, but native Windows file permissions use a different security model.