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File Permissions

File Permissions

by David Stanley

CHMOD for PHP is the same concept as the CHMOD for Perl/CGI.

Permissions are set using a command called CHMOD. CHMOD stands for CHange MODe. You are giving the host computer new instructions about this file or directory.

CHMOD comes as a set of 3 numbers. Each of these 3 numbers is a sum total of 3 other numbers. So you have to add 3 numbers to get the first CHMOD number, add 3 numbers to get the second CHMOD number and add 3 numbers to get the third CHMOD number.

Understanding the numbers...

Each digit is a number value from 0 to 7. The value specifies what capabilities are available (or not). These numbers correspond to 3 command types. Read, write and execute.

Read (r) has a value of 4. It allows listing files in the directory.
Write (w) has a value of 2. It allows the addition of new files to the directory.
Execute (x) has a value of 1. It allows access to the files in the directory.

Here are the possible combinations available using these command types :

Digit	rwx	Result
0	---	no access
1	--x	execute
2	-w-	write
3	-wx	write and execute
4	r--	read
5	r-x	read and execute
6	rw-	read and write
7	rwx	read write execute

OK... so you know each digit will be a number from 0 to 7, but what does the 3 digits stand for?

The first number represents the host server. This will usually be set to 7 giving the host full permission on the files in the folder. The second number represents the group (YOU - the individual being hosted). And the third number represents the world (the visitors to the site). Normally, on free hosts, these two digits will be set to 4, allowing the reading (and displaying) of files. Thus, no executing capabilities.

Typical settings for files are 777, 755, 666 or 644.
Typical settings for directories are 777 or 755.
Cgi scripts 755, data files 666, and configuration files 644.

How do you change the CHMOD?

The easiest way (for a user) is by using an FTP program. Most FTP programs have a button or right-click menu that allows you to set the CHMOD on a specific folder. You may have to contact your host to find an alternate way of doing this.