What does chmod 755 mean?

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+0+1). In symbolic form it is -rwxr-xr-x. It is the standard permission for directories and executable scripts: the owner has full control and everyone else can enter or run, but not modify.

What is the difference between 644 and 755 permissions?

644 (-rw-r--r--) gives the owner read and write, and everyone else read-only — the right setting for regular files like HTML, images and configs. 755 (-rwxr-xr-x) adds the execute bit for all three classes, which directories need to be entered and scripts need to be run. Use 644 for files and 755 for folders.

How do I calculate chmod permissions by hand?

Give read = 4, write = 2, execute = 1, then add the values you want for each class. Owner rwx = 4+2+1 = 7; group r-x = 4+1 = 5; other r-x = 5. Write the three digits in order owner-group-other to get 755. Repeat for any combination — each digit is always between 0 and 7.

What does chmod 777 do and is it safe?

777 (-rwxrwxrwx) gives read, write and execute to the owner, the group and everyone else. It is almost never safe: any user on the system — and any compromised process — can overwrite or replace the file. For web hosting use 644 for files and 755 for directories. If a tutorial tells you to use 777, treat it as a red flag.

How do I convert symbolic permissions (rwxr-xr-x) to octal?

Split the 9 characters into three triads — rwx, r-x, r-x. For each, add 4 for r, 2 for w, 1 for x: rwx = 7, r-x = 5, r-x = 5, giving 755. Paste the symbolic string into the calculator above and it does the conversion instantly, in both directions.

What are the setuid, setgid and sticky bits?

They are three extra permission bits stored in a leading 4th octal digit: setuid (4) runs an executable as its owner, setgid (2) runs it as its group or makes new files in a directory inherit that group, and the sticky bit (1) stops users deleting files they do not own in a shared directory like /tmp. So 1777 is /tmp and 4755 is a typical setuid binary.

Why does my symbolic string show s or t instead of x?

Those mark the special bits. A lowercase s in the owner or group execute slot means setuid or setgid with execute on; capital S means the special bit is set but execute is off. A lowercase t in the others slot is the sticky bit with execute on; capital T is sticky with execute off. The calculator labels each one in the explainer panel.

Does this chmod calculator send my input anywhere?

No. Every conversion runs in your browser with plain bit arithmetic — there is no server call, no upload and no logging. You can disconnect from the internet and it still works. The page is open about its sources: the POSIX, Linux man-page and GNU Coreutils references are linked below.

Developer · Utility

Chmod Calculator — Linux File Permission Calculator

Tick the read, write and execute bits for owner, group and other to get the octal code (755), the symbolic string (-rwxr-xr-x) and the exact chmod command. Paste an octal code or an ls -l string and it decodes the other way. Runs in your browser, no signup.

By Induwara Ashinsana— Executive Director, Ryzera TechnologiesUpdated Jun 11, 2026

Chmod permission calculatoroctal ↔ symbolic

Class

Read

Write

Execute

Owner

Group

Others

Special bits

Octal code

1–4 digits, each 0–7. A 4th leading digit sets special bits.

Symbolic string

9 characters, ls -l style. Paste rwxr-xr-x or -rwxr-xr-x.

Common

Octal

644

With special bits

0644

Symbolic

-rw-r--r--

Assignment

u=rw,g=r,o=r

Run this command

chmod 644 filename

chmod u=rw,g=r,o=r filename

Who can do what

Class

Read

Write

Execute

Owner

Group

Others

Runs entirely in your browser — nothing is uploaded. Values follow the POSIX and GNU Coreutils sources cited below the calculator.

How it works

A Linux file carries nine permission bits — read, write and execute for three classes of user: the owner, the file's group, and everyone else (others). The chmod command sets those bits, and this calculator converts between the two notations people use to express them: octal and symbolic.

Each permission has a value. Read = 4, write = 2, execute = 1. These are the mode-bit constants in the Linux chmod(2) man page.
Add the values per class. For each of owner, group and other, sum the bits you want. Owner rwx = 4+2+1 = 7; a group with r-x = 4+0+1 = 5. Every digit lands between 0 and 7.
Concatenate owner-group-other. Write the three digits in order to get the octal code, e.g. 7,5,5 → 755.
Special bits become a leading 4th digit. setuid = 4, setgid = 2, sticky = 1, summed into an optional first digit: 4755, 1777. These map to the kernel constants S_ISUID (04000), S_ISGID (02000) and S_ISVTX (01000).
Symbolic rendering. Each bit becomes r/w/x or a dash. A special bit overlays the execute slot per the GNU Coreutils manual: setuid/setgid show s when execute is on or S when it is off; the sticky bit shows t or T in the others slot.
Decoding is the reverse. An octal string is split right-to-left into other, group and owner digits (plus an optional special digit), and each digit is decomposed by testing the 4/2/1 bits. A 9-character symbolic string is read slot by slot, treating s/tas “special + execute on” and S/Tas “special, execute off”.

The whole computation is exact integer arithmetic — no rounding and no external data, so the result never goes stale. The calculator also runs an internal consistency check: it re-derives the octal value from the symbolic string it just rendered and confirms the two agree, the same cross-check used in the worked examples below.

Worked examples

755 — directories and scripts

755-rwxr-xr-x

Owner rwx = 4 + 2 + 1 = 7
Group r-x = 4 + 0 + 1 = 5
Other r-x = 4 + 0 + 1 = 5
Concatenate → 755, symbolic -rwxr-xr-x
Command: chmod 755 script.sh

644 — regular files (the default)

644-rw-r--r--

Owner rw- = 4 + 2 + 0 = 6
Group r-- = 4 + 0 + 0 = 4
Other r-- = 4 + 0 + 0 = 4
Concatenate → 644, symbolic -rw-r--r--
Only the owner can edit; everyone else is read-only.

4755 — setuid binary (e.g. /usr/bin/passwd)

4755-rwsr-xr-x

Special: setuid = 4 → leading digit
Base 755 as above
Execute is on in the owner slot, so x becomes a lowercase s
Concatenate → 4755, symbolic -rwsr-xr-x
Command: chmod 4755 /usr/bin/passwd

1777 — sticky directory (e.g. /tmp)

1777drwxrwxrwt

Special: sticky = 1 → leading digit
Base 777 (rwx for all three classes)
Others execute is on, so x becomes a lowercase t
Concatenate → 1777, symbolic drwxrwxrwt for a directory
Everyone can write, but only an owner can delete their own files.

Frequently asked questions

Sources & references

The bit values, symbolic-rendering rules and worked examples on this page were last cross-checked against these sources on 2026-06-11. The chmod specification has been stable for decades, so this tool needs no rate or data updates.

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