chmod Calculator (octal + symbolic)
Check the boxes or type an octal value. Live octal, symbolic string, and a ready chmod command.
| Class | Read (4) | Write (2) | Exec (1) |
|---|---|---|---|
| Owner | |||
| Group | |||
| Other |
chmod 644 file What this tool does
A chmod calculator turns Unix file permissions between the two forms people
actually use. Tick the boxes for read, write, and execute across the owner,
group, and other classes and the tool prints the octal mode (such as
755) and the symbolic string (such as rwxr-xr-x)
as you go. Type an octal value instead and the checkboxes and symbolic form
update to match. An optional row of special bits (setuid, setgid, sticky)
produces the four-digit mode like 4755 and the matching
s, S, t, and T letters.
Everything is computed in your browser; nothing is uploaded.
How to use it
Toggle any checkbox to build a mode from scratch: read is worth 4, write is
worth 2, and execute is worth 1, so each class becomes a single digit from 0
to 7. Or type a mode into the Octal value box (three digits
like 644, or four like 0644 or 4755)
and the grid updates to match. The Symbolic line shows the
rwx letters, and the Command line gives a
ready-to-run chmod 755 file example you can copy and adapt.
Common use cases
- Working out the octal mode to hand to
chmodwhen you only know which access you want. - Reading a symbolic string from
ls -l(likerwxr-xr-x) back into a number. - Setting a private key to
600or a directory to755without second-guessing the digits. - Understanding what the setuid, setgid, or sticky bit does to a mode before you apply it.
- Teaching or documenting how Unix permission bits map to numbers.
Common pitfalls
- Execute means different things. On a file, execute lets you
run it; on a directory, it lets you enter the directory and reach files by
name. A directory usually needs execute wherever it has read, which is why
755and700are common directory modes. - 777 is almost never right. Granting write to everyone is a
frequent source of security problems, especially on a web server. Reach for
the least permission that works: usually
644for files and755for directories. - Uppercase S or T signals a missing execute bit. When a
special bit is set but the underlying execute bit is off, the symbolic form
shows
SorTinstead ofsort. That is usually a mistake worth fixing, not a feature. - This is not the same as ownership. chmod changes permission
bits, not who owns the file. Changing the owner or group is a separate step
with
chownorchgrp.
Frequently asked questions
- What does chmod 755 mean?
- chmod 755 sets the permission string rwxr-xr-x. The owner gets read, write, and execute (7 = 4 + 2 + 1). The group and everyone else get read and execute but not write (5 = 4 + 1). It is the usual mode for directories you want others to enter and for scripts or binaries that anyone may run.
- What is the difference between octal and symbolic notation?
- They describe the same permissions two ways. Octal packs each of the three permission classes into one digit from 0 to 7, so 644 is three digits. Symbolic spells out every bit as a letter, so 644 becomes rw-r--r--, where r is read, w is write, x is execute, and a hyphen means the bit is off. This calculator shows both at the same time.
- What do read, write, and execute mean for a directory?
- On a directory the bits behave differently than on a file. Read lets you list the names inside it. Write lets you create, rename, or delete entries. Execute (the search bit for directories) lets you enter the directory and reach files by name. You usually need execute on a directory for read to be useful, which is why directory modes are commonly 755 or 700.
- What are the setuid, setgid, and sticky bits?
- They are the optional fourth octal digit. setuid (4) makes an executable run as its owner, setgid (2) makes it run as its group or makes new files in a directory inherit that group, and the sticky bit (1) on a shared directory stops users from deleting each other's files. In symbolic form they replace the execute letter with s, s, and t; the letter is uppercase (S or T) when the underlying execute bit is off.
- What is the difference between chmod 644 and chmod 755?
- 644 is rw-r--r--: the owner can read and write, everyone else can only read, and nobody can execute. It suits ordinary data files such as text, HTML, or images. 755 is rwxr-xr-x: it adds execute for all three classes, which is what you want for directories and for programs or scripts meant to be run.
- Why is chmod 777 considered risky?
- 777 is rwxrwxrwx, which grants read, write, and execute to everyone on the system. Any local user can then modify or replace the file, and on a web server a writable executable is a common path to compromise. Prefer the least permission that works, usually 644 for files and 755 for directories, and reserve group or other write for the rare cases that truly need it.
- How do I read a symbolic string like rwxr-xr-x?
- Split it into three groups of three after any leading file-type character. The first triplet is the owner, the second is the group, and the third is everyone else. Within each triplet the order is always read, write, execute. So rwxr-xr-x means the owner has all three, while group and other have read and execute only, which equals 755.
Cite this tool
For academic, journalistic, or technical references. Pick a format:
Citations use 2026 as the publication year. Access date is left as a fillable placeholder where the citation style expects one.