What is chmod?
chmod ("change mode") is a Unix/Linux command for changing file and directory permissions. This calculator lets you move between numeric permissions like 755, symbolic permissions like rwxr-xr-x, and the checkbox matrix without doing the mental math by hand.
How numeric permissions work
Each numeric digit represents one role: owner, group, and others. Inside each digit, 4 means read, 2 means write, and 1 means execute. Add the values together to build the permission you want: 7 = rwx, 6 = rw-, 5 = r-x, and 4 = r--. For directories, the execute bit also allows entering the directory.
Common chmod examples
- chmod 755 script.sh gives the owner full access and lets everyone else read and execute.
- chmod 644 notes.txt keeps a file writable by the owner while everyone else can only read it.
- chmod 600 .env is a common choice for private secrets because only the owner can read or write it.
- chmod 775 shared-folder is useful for team directories when the group should also be able to create and modify files.