How Linux octal permissions map to read, write and execute
A chmod permissions calculator translates access flags into the octal number used by the Linux chmod command. Each ordinary permission group has three bits: read contributes four, write contributes two, and execute contributes one. Add the enabled values for the owner, group, and others separately. For example, 755 grants the owner all three permissions while group members and other users receive read and execute. The symbolic output spells those choices as rwxr-xr-x, preceded here by a dash to represent a regular file. This tool calculates a representation; it never inspects your filesystem or executes a shell command.
File and directory permissions have different practical effects. Reading a regular file allows access to its contents, while directory read permission allows listing its entries. Directory execute permission permits searching or traversing the directory, and directory write permission relates to adding or removing entries. Ownership, access control lists, mount options, and other security mechanisms can affect the effective outcome. A permission number therefore does not completely describe who can reach a file. Before applying a command, inspect the actual path, its parent directories, and the ownership expected by your application or service.
The optional leading digit combines SetUID, SetGID, and the sticky bit. Symbolic notation replaces selected execute positions with s or t when both the special and execute bits are set, or uppercase S and T when execute is absent. These flags are context-sensitive and deserve deliberate review. The common 644, 755, and 600 presets are starting points for comparison, not universal deployment instructions. The 777 preset illustrates unrestricted ordinary permission bits; using it to resolve an access error can introduce unintended write access. Prefer the least permissions that match the intended task and verify behavior after an authorized change.
Quick reference table
| Octal | Binary | Symbolic |
|---|---|---|
| 0 | 000 | --- |
| 1 | 001 | --x |
| 2 | 010 | -w- |
| 3 | 011 | -wx |
| 4 | 100 | r-- |
| 5 | 101 | r-x |
| 6 | 110 | rw- |
| 7 | 111 | rwx |
Further reading: GNU Coreutils: file permissions.
How to use Chmod Permissions Calculator
1. Enter your values
Enter three or four octal digits, or start from a common preset. Only digits zero through seven belong in octal notation; an incomplete or invalid value produces a visible error instead of an assumed permission set.
2. Compare the result
Toggle read, write, and execute for the owner, group, and others. Review special permission bits separately. The numeric and symbolic representations update together, so you can compare the effect of each individual checkbox.
3. Review before use
Copy the command preview and replace the file-name placeholder with the intended, safely quoted path. Review ownership and directory access first. The calculator neither runs chmod nor confirms that the resulting permissions are appropriate for your environment.
Key features and technical specifications
Instant local calculation
Inputs update the result directly in your browser without a processing API or account.
Theme-aware interface
Controls follow the site theme, with explicit labels and readable results on mobile screens.
Apply the result in context
Review the assumptions beside the result, and use consistent input units when comparing scenarios.
Compare alternatives
Change one input at a time to understand which assumptions drive the difference between two scenarios.
Explain the calculation
Use the reference table and examples to connect the displayed output with the underlying rules.
Frequently asked questions
What does chmod 755 mean?
The owner has read, write and execute; the group and others have read and execute. Whether execute is needed depends on whether the target is a program, script, or directory. It is not a default permission for every file.
What is the difference between 644 and 600?
Both grant owner read and write. With 644, group members and others also receive read permission; with 600 they receive none of the ordinary permission bits. Actual access still depends on directory traversal, ownership, ACLs, and other controls.
Why do I see uppercase S or T?
Uppercase means the corresponding special bit is set while the execute bit in that position is not. Lowercase s or t means both are enabled. This distinction preserves information that a simple read/write/execute-only representation would lose.
Should I use chmod 777 to fix permission errors?
Not as a blanket fix. It permits every ordinary permission class to write and execute. First determine the process identity, file ownership, parent-directory access, and required operation, then choose a narrower permission set that addresses the actual problem.
Does this page change my files?
No. It only transforms the values you enter in browser memory. Copying the preview puts text on your clipboard; it does not start a terminal or change a file. No filename or permission choice is sent to a processing API.