On Unix-like systems, permissions say who can read, change, or run a file. chmod Calculator shows the three-digit number and the rwx letters side by side. It does not change any file by itself.
Read 755
The Octal box starts at 755. Under Symbolic, look for rwxr-xr-x. Read it in three groups: rwx for the file’s user (owner), r-x for its group, and r-x for others. r means read, w write, and x execute. The Command row shows chmod 755 <file>: <file> is a placeholder you would replace with a real path after checking it.
Now type 644 in Octal. The result should become rw-r--r--: the owner can read and write; group and others can only read. Tick a permission checkbox to see the number change. Recheck the command before running it, especially on directories or shared files.
Important limit
This tool displays the last three permission digits only. A fourth, leading digit for special bits (such as the sticky bit in 1777) is not preserved in the shown result or command. Do not rely on it to plan setuid, setgid, or sticky-bit permissions. The Special row does not correctly detect those bits.
Where your input goes
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Related guide
For more background, read Linux Command Line Tasks Without Surprises.
Questions you might have
- What is the difference between 644 and 755?
- 644 gives the owner read and write and everyone else read, which is the normal choice for files. 755 adds execute for everyone, which is what directories and scripts need.
- What does a leading digit mean?
- In a full Unix permission number, the leading digit can hold setuid, setgid, and sticky bits. This calculator does not preserve or report that digit correctly. Check special bits using system tools before changing permissions.