liminfochmod Calculator
Free web tool: chmod Calculator
| Read (4) | Write (2) | Execute (1) | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Other |
Octal
755
Symbolic
rwxr-xr-x
chmod Command
chmod 755 filenameAbout chmod Calculator
The chmod Calculator is a free, browser-based tool that translates Unix/Linux file permission checkboxes into the octal number and symbolic string used by the chmod command. Instead of mentally calculating 4+2+1 for each of the Owner, Group, and Other columns, you simply toggle the Read, Write, and Execute checkboxes and the tool does the arithmetic for you — delivering both the three-digit octal code (e.g., 755) and the nine-character symbolic notation (e.g., rwxr-xr-x) in real time.
System administrators, DevOps engineers, and software developers use this tool when setting up web server directories, SSH keys, executable scripts, or any file that requires precise access control on POSIX-compliant systems. It is especially helpful for those who are still learning Unix permissions, because the visual checkbox layout makes it immediately obvious which combination of bits produces a given octal value.
Under the hood, each row's three bits map to a single octal digit: read contributes 4, write contributes 2, and execute contributes 1. The tool sums those values per role and concatenates the three digits to form the final permission code. It also assembles the nine-character symbolic string by substituting "r", "w", "x" or "-" for each position. The resulting chmod command — e.g., `chmod 755 filename` — is displayed and can be copied to the clipboard with one click.
Key Features
- Checkbox grid for Owner, Group, and Other — toggle Read (4), Write (2), Execute (1) independently
- Real-time octal output (e.g., 755, 644, 600) updated on every checkbox change
- Real-time symbolic notation output (e.g., rwxr-xr-x) alongside the octal value
- Ready-to-use chmod command displayed as `chmod NNN filename` for direct terminal paste
- One-click copy buttons for octal, symbolic, and full chmod command strings
- 100% client-side — no data ever leaves your browser
- Responsive layout that works on mobile, tablet, and desktop screens
- Dark mode support for use in terminal-heavy, low-light work environments
Frequently Asked Questions
What does chmod mean?
chmod stands for "change mode" — a Unix command that changes the access permissions of files and directories. Permissions control which users can read, write, or execute a file, and are divided into three categories: Owner (the file's creator), Group (users in the file's assigned group), and Other (everyone else).
How do I read a three-digit octal like 755?
Each digit corresponds to one role: the first digit is Owner, the second is Group, the third is Other. Within each digit, the value is the sum of active bits: Read=4, Write=2, Execute=1. So 7 means all three (4+2+1), 5 means Read+Execute (4+1), and 4 means Read only.
What is the difference between octal and symbolic notation?
Both represent the same permissions in different formats. Octal uses three digits (e.g., 755) — concise and widely used in command lines. Symbolic uses nine characters (e.g., rwxr-xr-x) that directly show which bits are set for each role, making it more human-readable.
What chmod value should I use for a web server public directory?
A common choice is 755 (rwxr-xr-x): the Owner can read, write, and traverse the directory; Group and Other can only read and traverse. For files within such a directory (not directories themselves), 644 (rw-r--r--) is typical — Owner can read and write, others can only read.
Why should I avoid chmod 777?
777 grants read, write, and execute permissions to everyone on the system, including untrusted users and processes. On a shared server this is a major security risk, as any user or compromised process can modify or delete the file. Use the least-privilege principle and only grant the permissions that are actually needed.
What does the execute bit mean for a directory?
For directories, the execute bit controls "traverse" permission — whether a user can cd into the directory or access files inside it. Without the execute bit, a user cannot enter a directory even if they have read permission on it.
Can I use this tool to set permissions for SSH keys?
Yes. SSH private keys (e.g., ~/.ssh/id_rsa) typically require chmod 600 (rw-------), meaning only the Owner can read and write the file. The public key (~/.ssh/authorized_keys) is usually set to 644. Using any broader permissions will cause SSH to refuse the key for security reasons.
Does this tool support special bits like setuid, setgid, or sticky bit?
The current version covers the standard three-role, three-permission model (nine bits). Special bits (setuid=4000, setgid=2000, sticky=1000) add a fourth leading octal digit and are not yet included in this calculator. You can manually prepend the appropriate digit to the generated octal value if needed.