Toggle read, write and execute for the owner, group and other, and read the chmod value both ways: the octal number (like 755) and the symbolic string (like rwxr-xr-x). You can also paste either form to fill the grid. Special bits — setuid, setgid and the sticky bit — are handled too. Everything runs in your browser.
| Class | Read | Write | Execute |
|---|---|---|---|
| Owner | |||
| Group | |||
| Other |
Octal
755
Symbolic
rwxr-xr-x
chmod 755 file
Read = 4, write = 2, execute = 1, added per class. Everything is computed locally in your browser.
How it works
Each of the three permission classes — owner, group and other — has three bits worth read = 4, write = 2 and execute = 1. Adding the ticked bits in a class gives one octal digit: read + write + execute is 4 + 2 + 1 = 7, read + execute is 4 + 1 = 5. Three classes give the familiar three-digit number, so rwx / r-x / r-x is 755.
A leading fourth digit carries the special bits: setuid = 4, setgid = 2 and the sticky bit = 1, so 4755 is 755 with setuid set. In symbolic form these replace the execute character: setuid and setgid show s (or S when execute is off) in the owner/group execute slot, and the sticky bit shows t (or T) in the other slot — which is why /tmp is drwxrwxrwt.
Practical examples
A normal executable or script — 755
Owner rwx, group r-x, other r-x is 755 (rwxr-xr-x). The owner can edit and run it; everyone else can read and run but not change it. This is the typical mode for programs and directories.
A private config file — 600
Owner rw-, group ---, other --- is 600 (rw-------). Only the owner can read or write it — the right mode for things like an SSH private key or a secrets file.
A shared temp directory — 1777
rwxrwxrwt is 1777: everyone can create files, but the sticky bit (the trailing t) means you can only delete your own. That is exactly how /tmp is set up.
Frequently asked questions
What does chmod 755 mean?
It sets read + write + execute for the owner (7), and read + execute for group and other (5 and 5). In symbolic form that is rwxr-xr-x. It is the standard for executables and directories: the owner controls them, others can use but not modify them.
What is the difference between 644 and 755?
644 (rw-r--r--) gives no execute bit — right for plain files like documents and images. 755 (rwxr-xr-x) adds execute for everyone — needed for programs, scripts and directories, since entering a directory requires the execute bit.
How do the octal numbers map to letters?
Each digit is read (4) + write (2) + execute (1) added together: 7 = rwx, 6 = rw-, 5 = r-x, 4 = r--, 0 = ---. The three digits are owner, group and other, in that order.
What are the setuid, setgid and sticky bits?
They are the optional fourth (leading) octal digit. setuid (4) runs a program as its owner; setgid (2) runs it as its group or makes new files in a directory inherit that group; the sticky bit (1) on a shared directory lets users delete only their own files.
Why does a permission show s or t instead of x?
Those mark the special bits in symbolic notation. A lowercase s in the owner or group execute slot means setuid/setgid with execute on; uppercase S means the bit is set but execute is off. Likewise t/T in the last slot is the sticky bit.
What permissions should a directory have?
Usually 755 (rwxr-xr-x). Directories need the execute bit to be entered and the read bit to be listed, so 644 would make a directory unusable. Use 700 for a private directory only you should enter.
Can I paste an existing permission to decode it?
Yes. Type an octal value (755 or 4755) or a symbolic string (rwxr-xr-x) into the import field and the grid fills in. A leading file-type character, like the - or d from ls -l, is accepted and ignored.
Is 777 safe to use?
Rarely. 777 (rwxrwxrwx) lets anyone read, change and run the file, which is a security risk on shared systems. It is a common quick fix for permission errors but almost always the wrong one — grant the narrowest access that works instead.
Does this send my values anywhere?
No. The calculation is pure arithmetic done in your browser; nothing you enter is uploaded and analytics never receives it.
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