Simplify Assigning Permissions with Chmod Calculator

If you use the command line and the chmod command to change permissions on your files, you know perhaps that there are two ways to do this: symbolic mode and absolute mode. Symbolic mode uses letters such as r, w, and x to indicate the permissions that you change for specific items. Absolute mode uses three-digit numbers to indicate the aggregate permissions for items. For example, running chmod 766 on a file gives it read, write and execute permission for the item’s owner, but only read and write permissions to the group and others.

Absolute mode can be easier to use, since you only have to worry about one three-digit number, but if you’re not used to working with it you’ll spend time calculating this number. It’s not rocket science – it’s merely the sum of the decimal equivalents of the binary numbers that represent the different permissions. These numbers are equal to 1 for the execute bit, 2 for the write bit and 4 for the read bit.

To streamline this calculation, at least until you become familiar with the permissions numbers you use often, you can use the freeware Chmod Calculator, a very simple tool that adds up the numbers for you. While this may seem like a bit of a crutch, it will help you prevent mistakes when you set permissions; something that could have serious effects on your Mac.

Just check off the different permissions and see what the resulting number is. Simple, effective, and it could save you headaches.

Read more articles in this category: Mac OS X Command Line