Chmod Calculator
Calculate Linux file permissions in octal and symbolic notation. Toggle read/write/execute for owner, group, and others, and copy the chmod command.
CHMOD Calculator
Calculate Linux file permissions in octal and symbolic formats.
| Entity | Read (4) | Write (2) | Execute (1) |
|---|---|---|---|
| user | |||
| group | |||
| other |
All processing happens locally in your browser — nothing is stored or sent to any server.
How to Use the Chmod Calculator
- Click the checkboxes to toggle read, write, and execute permissions for each entity.
- See the octal notation update automatically (e.g. 755).
- View the symbolic notation and the ready-to-use chmod command.
About Linux File Permissions
Linux file permissions are represented in octal (base-8) notation where read=4, write=2, and execute=1. Each permission class (owner, group, others) gets its own octal digit by summing the active bits. So rwx = 4+2+1 = 7, and rw- = 4+2 = 6.
The three classes control access for different users: the owner (whoever created the file), the group (a named group the owner belongs to), and others (everyone else on the system). On a web server, files are often owned by the deployment user and read by the web server process (e.g. www-data).
Commonly used permissions: 644 for regular files (owner writes, everyone reads), 755 for directories and executables (owner full access, others read+execute), 600 for private files like SSH keys or .env files (owner only), and 400 for read-only private files. Avoid 777 on any production system.
Frequently Asked Questions
What does chmod 755 mean? ▼
755 means the owner has full read/write/execute permissions (rwx = 7), while group and others have read and execute only (r-x = 5). It is the standard permission for web server directories and executable scripts.
What do the digits 4, 2, and 1 represent? ▼
Read = 4, Write = 2, Execute = 1. Each permission group (owner, group, others) is the sum of these values. rwx = 7, rw- = 6, r-x = 5, r-- = 4, --x = 1, --- = 0.
What is the most secure default permission for files? ▼
644 for files (owner can read and write, group and others can only read) and 755 for directories. Never use 777 on a web server — it gives full read/write/execute to everyone, including potential attackers.
What does chmod 777 mean? ▼
777 gives full read/write/execute permissions to everyone — owner, group, and all other users. This is a significant security risk on shared servers or web directories. Use 644 for files and 755 for directories in most cases.
What is the difference between symbolic and octal notation? ▼
Octal notation uses digits (e.g. 755). Symbolic notation uses letters and operators (e.g. rwxr-xr-x). Both describe the same permissions. This calculator shows both formats and the ready-to-use chmod command.
Why does execute permission matter for directories? ▼
For directories, execute permission means the ability to enter (cd into) the directory. Without it, users cannot access the directory's contents even if they have read permission. That is why directories typically use 755 instead of 644.
What are sticky bits and setuid? ▼
These are special permission bits beyond the basic rwx. The sticky bit (1000) on a directory means only the file owner can delete their own files. setuid (4000) lets a program run as the file's owner. setgid (2000) lets programs run as the file's group. This calculator handles the standard rwx permissions.
Can I use this to generate the full chmod command? ▼
Yes. The tool displays the exact chmod command (e.g. chmod 755 filename) ready to copy and paste into your terminal.