Chmod
Convert Unix chmod file permissions between symbolic rwx and octal values instantly. Set read write and execute for user group and others with charts.
Who can read?
Who can write?
Who can execute?
Special modes
About This Calculator
The Chmod Calculator (short for change mode) converts Unix and Linux file permissions between symbolic notation (rwx) and octal values (755). Whether you are a system administrator configuring server file permissions, a developer setting up a web application, a DevOps engineer troubleshooting access issues, or a student learning Linux fundamentals, this tool helps you instantly translate between permission formats and construct the exact chmod command you need.
Chmod permissions are based on three classes: the user/owner who created the file, the group assigned to the file, and others (everyone else). Each class can be granted three permissions: read (r, value 4) to view file contents, write (w, value 2) to modify or delete the file, and execute (x, value 1) to run the file as a program or traverse a directory. The octal value is the sum of these permission values for each class — for example, read+write+execute = 4+2+1 = 7, while read+execute = 4+1 = 5.
This calculator supports two modes. In Find chmod command mode, you toggle yes/no dropdowns for each permission across all three classes, plus optional special modes (setuid, setgid, sticky bit). The result shows the complete chmod command, symbolic string, binary representation, and a detailed breakdown. In Decode octal number mode, enter any 3 or 4-digit octal value (like 644, 777, or 2755) to instantly see what permissions it grants. Special modes are encoded in a leading fourth digit: setuid adds 4, setgid adds 2, and sticky bit adds 1.
Regional Notes
Chmod is a universal standard across all Unix, Linux, and macOS systems. The permission system is identical worldwide regardless of geographic region, language, or currency. System administrators in India, the United States, the United Kingdom, and everywhere else use the same rwx notation and octal values. This calculator works the same way for all users globally.
Frequently Asked Questions
What does chmod mean?
Chmod (short for change mode) is a Unix and Linux command used to change the permissions of files and directories. It controls who can read, write, or execute a file. Permissions are assigned to three classes: the user/owner of the file, the group, and all other users.
How do I convert chmod 755 to symbolic notation?
Chmod 755 in symbolic notation is rwxr-xr-x. The first digit (7 = rwx) gives the owner read, write, and execute permissions. The second digit (5 = r-x) gives the group read and execute permissions. The third digit (5 = r-x) gives others read and execute permissions. Each octal digit is the sum of read (4), write (2), and execute (1) values.
What is the difference between chmod 777 and chmod 755?
Chmod 777 (rwxrwxrwx) gives read, write, and execute permissions to everyone — owner, group, and others. Chmod 755 (rwxr-xr-x) gives full permissions to the owner but only read and execute to group and others. Chmod 777 is less secure because anyone can modify the file, while 755 is the standard for executable files and directories on web servers.
What does chmod 644 mean?
Chmod 644 (rw-r--r--) gives the owner read and write permissions (6 = 4+2), while the group and others get read-only permission (4). This is the standard permission for regular files like HTML, CSS, text files, and images. It allows the owner to modify the file while preventing anyone else from making changes.
What are setuid, setgid, and sticky bit?
Setuid (set user ID) allows a program to run with the permissions of the file owner, not the user running it. Setgid (set group ID) makes a program run with the file group's permissions, and on directories, new files inherit the directory's group. The sticky bit (restricted deletion) on directories like /tmp prevents users from deleting files owned by other users, even if they have write permission on the directory.
How do I calculate chmod permissions?
To calculate chmod permissions, assign a numeric value to each permission: read = 4, write = 2, execute = 1. Sum these values for the owner, then the group, then others. For example, if the owner needs read+write+execute (4+2+1=7), the group needs read+execute (4+1=5), and others need read+execute (4+1=5), the result is chmod 755. Use this calculator to set permissions with yes/no toggles or decode any octal value instantly.
What is the binary representation of chmod permissions?
Chmod permissions in binary represent each permission as a single bit: read (bit 2, value 4), write (bit 1, value 2), execute (bit 0, value 1). Each class gets 3 bits. For chmod 755: owner = 111 (binary), group = 101 (binary), others = 101 (binary), so the full binary string is 111101101. This calculator shows both octal and binary representations side by side.
What are the recommended chmod permissions for a web server?
For typical Linux web servers: directories should be 755 (rwxr-xr-x) so the owner can write and everyone can traverse. Files should be 644 (rw-r--r--) so the owner can edit and others can read. Configuration files should be 600 (rw-------) to restrict access. Executable scripts should be 755. Never use 777 on production files as it allows anyone to modify them.