How to use the chmod permissions calculator
- Tick read, write and execute for the owner, the group and others. The octal number and symbolic form update as you click.
- Or type an octal value such as 644 or 4755 and the boxes follow. Use a common set from the buttons if it fits.
- Open the special bits to set setuid, setgid or the sticky bit, which add a leading digit.
- Enter a file or folder name and copy the ready chmod command. Tick the recursive box only when you mean to change everything inside a folder.
Formula
Read = 4, write = 2, execute = 1; add them for each of owner, group and others
755 = rwx (4+2+1) for the owner, r-x (4+1) for the group and for others
Special bits: setuid = 4, setgid = 2, sticky = 1, added as a leading digit
Symbolic: s or S replace the owner or group x for setuid and setgid; t or T replace the others x for the sticky bit
A lowercase s or t means execute is also set. An uppercase S or T means the special bit is set without execute.
Worked example
Permissions 755 give the owner read, write and execute (7), and the group and others read and execute (5), shown as rwxr-xr-x. The command is chmod 755 script.sh.
644 is rw-r--r--, 600 is rw-------, 4755 is rwsr-xr-x with setuid, and 1777 is rwxrwxrwt with the sticky bit, the usual setting for a shared temporary folder.
Reading an octal permission
Each digit stands for one class of user: the first is the owner, the second the group and the third everyone else. A digit is the sum of the bits that class has. A file the owner can edit and everyone can read is 644. A script that everyone can run but only the owner can edit is 755. A private file is 600.
Be careful with 777 and recursive changes
777 lets any user on the system change or run the file, which is rarely needed and can be unsafe. Running chmod with -R on the wrong folder can break an installation by making files executable or unreadable. Check the path before you press enter, and prefer the narrowest permission that works.
Related tools
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Assumptions and limits
- The permissions are the classic Unix owner, group and others bits. Access control lists, file attributes and mount options are not covered.
- The command is for a POSIX shell such as bash or zsh. Names with spaces or special characters are quoted for you.
- Octal input must be three or four digits from 0 to 7.
- Always review the command before running it, especially with the recursive option.
Frequently asked questions
What does chmod 755 mean?
The owner can read, write and execute, while the group and others can read and execute but not write. It is common for programs and folders.
What does chmod 644 mean?
The owner can read and write, and the group and others can only read. It is a typical setting for ordinary files.
What do the setuid, setgid and sticky bits do?
Setuid and setgid make a program run with the file owner or group privileges, and the sticky bit on a folder lets only a file's owner delete it. Use them only when you understand the effects.
How do I make a file executable?
Give it execute permission, for example chmod 755 for everyone to run it, or chmod 700 so only you can. The tool builds the command.