Chmod Calculator
Convert between octal (755) and symbolic (rwxr-xr-x) Linux file permissions. Tick the boxes or type a number — everything updates instantly.
| Role | Read (4) | Write (2) | Execute (1) | Digit |
|---|---|---|---|---|
| Owner (u) | 0 | |||
| Group (g) | 0 | |||
| Others (o) | 0 |
Octal
000
Symbolic
---------
chmod 000 filename
What Are Linux File Permissions?
Every file and directory on a Linux or Unix system has a set of permissions that control who can read, write, or execute it. Permissions are defined for three roles: the file's owner (user), the file's group, and others (everyone else). The chmod (change mode) command sets these permissions, and this calculator converts between the two ways of expressing them — octal numbers and symbolic rwx strings.
Everything runs locally in your browser. No data is sent anywhere — this is a pure JavaScript calculator.
How to Use This Tool
- Tick the read / write / execute boxes for owner, group, and others — or
- Type an octal value like
755in the Octal field, or a symbolic string likerwxr-xr-xin the Symbolic field. - Optionally enable the special setuid, setgid, or sticky bit checkboxes.
- Copy the ready-to-paste
chmodcommand at the bottom.
How the Octal Number Works
Each permission is a power of two: read = 4, write = 2, execute = 1. Add them up per role to get a single digit between 0 and 7:
7= read + write + execute (rwx)6= read + write (rw-)5= read + execute (r-x)4= read only (r--)0= no access (---)
Common Permission Values
644(rw-r--r--) — Regular files: documents, web pages, config files. Owner edits, everyone reads.755(rwxr-xr-x) — Directories and executable scripts. Owner has full control, others can read/run.600(rw-------) — Private files like SSH keys and credentials. Only the owner can read or write.700(rwx------) — Private directories. Only the owner can access anything inside.777(rwxrwxrwx) — Full access for everyone. Almost always a security mistake — avoid it.1777(rwxrwxrwt) — World-writable directory with the sticky bit, like/tmp.
Special Permission Bits
- setuid (4000) — An executable runs with the privileges of its owner, not the user running it. Shown as
sin the owner's execute position (e.g.,rwsr-xr-x). - setgid (2000) — Runs with the group's privileges; on a directory, new files inherit that directory's group. Shown as
sin the group's execute position. - sticky bit (1000) — On a shared directory, only a file's owner can delete or rename it. Shown as
tin the others' execute position.
Frequently Asked Questions
755 means the owner can read, write, and execute (7 = 4+2+1), while the group and others can read and execute but not write (5 = 4+1). In symbolic notation this is
rwxr-xr-x. It is the standard permission for directories and executable scripts that everyone should be able to run but only the owner should modify.644 means the owner can read and write (6 = 4+2), while the group and others can only read (4). In symbolic notation this is
rw-r--r--. It is the standard permission for regular, non-executable files such as documents, HTML pages, and configuration files.Each permission has a value: read = 4, write = 2, execute = 1. Add the values for each role (owner, group, others) to get one digit. For example, read + write + execute = 4 + 2 + 1 = 7, and read + execute = 4 + 1 = 5. The three digits together form the permission, such as 755.
They are special permission bits represented by an optional fourth leading octal digit. setuid (4000) runs an executable with the file owner's privileges. setgid (2000) runs with the group's privileges, or on a directory forces new files to inherit the directory's group. The sticky bit (1000) on a directory like
/tmp lets users delete only their own files. For example, chmod 1777 /tmp sets full permissions plus the sticky bit.Octal mode (e.g.,
chmod 644 file) sets the entire permission set at once using numbers. Symbolic mode (e.g., chmod u+x file) adds, removes, or sets specific permissions for specific roles using letters: u (user/owner), g (group), o (others), a (all), with + (add), - (remove), = (set exactly), and r/w/x for the permissions. Symbolic mode is useful when you want to change one permission without affecting the others.