If you’ve ever wondered why “chmod” was the name given to changing a file’s permissions, here you go. The “mod” is for “mode”; you’re changing the mode.

The mode can only be changed by the owner of the file. You’ll get a return value of false if this function fails to change the mode.

Be sure to give the mode as an octal. That means you’ll have four digits - the first one being a zero and the others 0-7.

What the numbers mean. If you can think in binary a little, it makes sense.

So a value of 4 is read only; a value of 2 is write only. Add them together and you get 6 which means read and write.

But you need to give three numbers for the mode of a file. You’re setting the mode for three entities: owner, group, and everyone else - in that order.

$file = '/home/my_file.txt';
 
chmod( $file, 0644 );
/*
owner: read + write
group: read
world: read
*/
 
chmod( $file, 0755 );
/*
owner: all
group: read + execute
world: read + execute
*/