Chmod Calculator
Tick read, write and execute for the owner, the group and others, or type an octal mode such as 755 or a symbolic one such as rwxr-xr-x, and the other forms update instantly. Special bits are supported too. The calculator writes the chmod commands, including find commands that give folders and files the right modes in a whole tree, and explains in plain words who can do what.
- Runs in your browser
- No sign-up
- Free to use
What it means
How to use Chmod Calculator
- Tick the permissions, type an octal mode or a symbolic one.
- Optionally set setuid, setgid or sticky.
- Enter the file or folder name.
- Copy the chmod command.
Chmod Calculator features
Three notations
Checkboxes, octal and symbolic stay in sync.
Special bits
setuid, setgid and sticky, shown as s, S, t and T.
Common modes
644, 755, 600, 700, 640, 775, 2775 and 1777 in one click.
Commands
Octal and symbolic chmod commands.
Folder trees
find commands with separate modes for folders and files.
Plain explanation
Who can read, write and execute, with warnings.
When to use Chmod Calculator
- Setting permissions for a website’s files and folders.
- Making a script executable.
- Protecting SSH keys and configuration files.
- Creating a shared folder for a team.
Chmod Calculator FAQ
What does chmod 755 mean?
The owner can read, write and execute (7 = 4 + 2 + 1); the group and others can read and execute (5 = 4 + 1). It is typical for scripts and folders.
What does chmod 644 mean?
The owner can read and write; everyone else can only read. It is the usual mode for web files and documents.
Which mode for SSH keys?
Private keys need 600 (owner read and write only); ssh refuses keys that others can read. The .ssh folder should be 700.
Why separate modes for folders and files?
Folders need execute permission to be entered, but ordinary files should not be executable. chmod -R 755 would make every file executable, so the find commands treat them separately.
What is the fourth digit?
The first of four digits holds the special bits: 4 setuid, 2 setgid, 1 sticky. 2775 is a shared group folder, 1777 is /tmp.
Why is 777 dangerous?
Everyone on the system can change or replace the file. Use group permissions instead.
Understanding chmod
chmod changes the permissions of files and folders on Linux, macOS and other Unix systems. Permissions are three sets of read, write and execute flags, for the owner, the group and everyone else, and can be written in two ways: octal digits, where read is 4, write 2 and execute 1 and the sums give one digit per class, or letters, such as rwxr-xr-x.
The calculator keeps all forms in sync. Ticking boxes updates the octal and symbolic values, typing 640 ticks the right boxes, and pasting the first ten characters of an ls -l line works as well. Common modes are one click away, each labelled with its typical use.
Special bits use a fourth, leading octal digit. setuid (4) makes an executable run with its owner’s rights, setgid (2) makes new files in a folder inherit its group, and the sticky bit (1) stops users from deleting other people’s files in a shared folder. In symbolic form they replace the execute letter with s or t, in capitals if execute is not set.
The commands include both notations: chmod 640 file and the equivalent chmod u=rw,g=r,o= file. For whole folder trees, applying one mode recursively is a common mistake, because folders need execute permission and files usually must not have it. The generated find commands give folders and files their own modes.
The explanation below the commands says in plain words who can read, change and run the file, and warns about modes that let everyone write, about setuid, and about execute without read, which scripts cannot use.