File permissions can be a large topic when it comes to web hosting, particularly on a UNIX server environment, such as the Personal Web Pages platform.
Permissions can be split into 3 types, that are applied across 3 types of users.
All files on a UNIX system have permissions, and these can be amended by using a command to change the file's mode. This is what is referred to as chmod.
Notation
The chmod command can take arguments of either numbers or letters. Letters are probably more logical to users that are not familiar with UNIX environments.
This table explains what the various numbers and letters represent:
You can add the numbers above to use multiple permissions - a 7 makes a file readable, writeable and executable; a 5 makes a file just readable and executable.
On a UNIX system environment, you will see permissions looking something like this:
The first character in the permissions section tells you what type of file it is. The above are all flat files other than "squirrel" which is a directory [hence it starting with a "d"].
From this point on in the permissions section there are 3 groups -- the user, the group and all others.
The user "alex" is the owner of the files, and the next 3 characters apply to him. If you look at the file mail_overquota.sh, "alex" can read from, write to and execute this file. Fellow members in the UNIX group "other" [next 3 characters] can read from it and execute [run the script], but not write to the file. The same is true for any other user on the file system.
Web servers run as special users with particular permissions on file systems. In the case of our platform, when a script is executed the web server runs the script "as" the user that uploaded it, so it inherits whatever permissions you give it.
Any entries with a "-" in them means that this is a blank space.Examples
Some examples are listed below of what various commands will do:
chmod +x filename
Make the file executable by all
chmod -x filename
Remove the executable permissions from the file
chmod 755 filename
Make the file readabale, writeable and executable by the owner [yourself], and readable and executable by all others [minimum requirement for most CGI scripts.
chmod 700 filename
Make a file readable, writeable and executable by the owner, and remove all permissions for all other users. "All others" would include the webserver if this is not a script.
Permissions could look like this on the server if you execute one of the above commands:
After a chmod 755: -rwxr-xr-x
After a chmod 700: -rwx------
As you can see, with a clear understanding of permissions, you can get to a very detailed structure of granularity for your file's permissions.
Using chmod in ftp programs
Many FTP programs allow you to run chmod commands.
