Chmod Calculator

chmod sets who may do what with a file on Linux, macOS and other Unix systems. Three kinds of user are told apart: the file's owner, its group, and everyone else, the public.

Each of the three may read, write and execute. As a number, read counts 4, write 2 and execute 1, and each kind of user gets the sum as one digit: 7 is all three, 5 is read and execute, 4 is read only.

• Tick the boxes, or type the number, such as 755, or the letters, such as rwxr-xr-x. A line copied from ls -l works too. File or Directory changes what each box means; the (i) beside a special bit explains it.
• Right under the fields, warnings appear as soon as the permissions let more people do more than intended, such as 777.
• Below: the chmod command as a number and in letters, with your file name and -R if you want it, and the stat command to check the result.
• Change with chmod applies a change such as g+w,o-rwx to the permissions above; umask shows what new files and directories get.
• A click on a value selects all of it, and the address bar follows.

• On a directory, read lists its names, write creates and deletes files in it, and execute lets you enter it.
• Setuid and setgid make a program run with its owner's or group's rights; setgid on a directory hands its group to new files. Sticky on a directory lets only a file's owner delete it, as on /tmp.
• The root user is not held back by these permissions.