Chmod Calculator: Unix File Permissions as Numbers and rwx
Tick read, write and execute for owner, group and others, or type 755 or rwxr-xr-x, and get the matching octal mode, ls string and chmod command.
Unix permissions have two spellings, the octal number chmod expects and the rwx string ls prints, and this calculator converts between them. Each of owner, group and others gets one digit: read is 4, write is 2 and execute is 1, added together. So rwxr-xr-x is 755 and rw-r--r-- is 644. Tick the boxes, or type a mode such as 755 or a string such as rwxr-xr-x, and the page shows the other forms and the chmod command.
Nothing leaves your browser and no file is touched: the page only rewrites the notation, and you run the chmod command yourself. Permission needs depend on your system, so check modes on servers, shared machines and anything holding secrets with whoever administers them before you apply them.
Permissions
755
rwxr-xr-x
chmod 755 file chmod u=rwx,g=rx,o=rx file
Decimal value 493
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About the Chmod Calculator
Unix permissions answer three questions for three kinds of user: can the owner, the file's group and everyone else read, write or execute the file. The POSIX standard for the chmod command gives each permission an octal value: 400, 200 and 100 for the owner's read, write and execute, 40, 20 and 10 for the group, and 4, 2 and 1 for others. A mode is the sum of the bits it sets, which is why each digit runs from 0 to 7 and 755 means 7 (4 + 2 + 1) for the owner and 5 (4 + 1) for the group and for others. A fourth digit in front holds the special bits: 4000 set user ID, 2000 set group ID and 1000 the sticky bit. In the string that ls -l prints, they show in the execute slot as s, s and t, or as capital S and T when the matching execute permission is off, which usually signals a mistake. The calculator follows the POSIX.1-2024 chmod and ls pages and writes both command forms, such as chmod 755 file and chmod u=rwx,g=rx,o=rx file; with special bits, the numeric form is the one every system reads the same way.
Frequently asked questions
What does chmod 755 mean?+
The owner can read, write and execute (7), and the group and everyone else can read and execute but not change the file (5 each). It is the usual mode for scripts, programs and directories that others need to open.
What is the difference between 644 and 600?+
Both let the owner read and write. 644 also lets the group and everyone else read the file, which suits web pages and ordinary documents; 600 shuts everyone else out, which suits private keys and files holding passwords.
Is chmod 777 safe?+
Rarely. It lets every account on the system change the file's contents, so a single compromised account can tamper with it. A narrower mode such as 755 or 775 is almost always enough; 777 on a shared or web-facing server is a common security hole.
What does the capital S or T in a permission string mean?+
It means a special bit is set but the execute permission under it is not. rwSr--r-- is set user ID on a file the owner cannot run, so the bit does nothing; a lowercase s or t means both are on.
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