Need help with understanding permissions in php and unix

[Ignus_Fatuus]

I have a huge problem understanding how permissions for directories and files works when php-scripting and ftp:ing respectively. I realized I didn't get it when I made a script that created certain directories on my account. I got it to create the dirs with full permissions and yet I can't delete them using my ftp-program.

Another thing is that files I upload from a html-form is created in the directories correctly, but they take no heed to the directories real chmod, as I see it from a ftp program. I have managed to set their CHMOD via the script so their CHMOD LOOKS like I can change it in FTP but I can't. It might have something to do with that I share the account with a friend who also uploads files through ftp and script to the directory and sometimes HE can change files via ftp but not I, and vice versa, even though we use the same account.

All this confuses me tremendously and I havnt found a good place to read about how these things work. What I really need is a tip of what I havnt understood, or a tip where I can read about this on different places on the net, so far I havn't found anything that pinpoints this exact problem.

[matt_4013]

When chmod'ing via a script, what you have to remember is that your web server usually runs with barely ANY permissions. For example, Most apache server's will run as the user "nobody". As such, any script that is running on this server, will also be running as the user "nobody", with the same permissions. So, for apache to change the permissions on a script not owned by the user "nobody", it must have world writeable permissions, ie, chmod 777

Unix permissions work like this:

A typical permission string for a file looks like this: -rwxr-xr-x

There are 4 sections there. The first specifies the file type. This section is 1 character long. It can be -, which is a normal file, d, which is a directory, l, which is a link, and many more.

The second section is 3 characters long (rwx). This tells what permissions the OWNER of the file has. Typically, this is read, write, and execute.

The 3rd section, is once again 3 characters long, and is the permissions that the GROUP has.

The last section, 3 chars long, is the permissions that EVERYBODY has.

So, if you have a file, owned by root, and it's group is webadmins, and you want root and web admins full access, but everybody to just have read and execute you would want the string:

-rwxrwxr-x

however, your web server wont be able to write to this. Only the owner and the group will. If you change it to -rwxrwxrwx everybody has full access to that file, and the web server will be able to write to it.

This php function will display the permissions of a file in unix format:

	function get_perms($file) {

	/* This function gets the permissions of a file and displays them in standard 
	UNIX format (drwxrwxr-x) */

	$p_bin = substr(decbin(fileperms($file)), -9) ;
	$p_arr = explode(".", substr(chunk_split($p_bin, 1, "."), 0, 17)) ;
	$perms = ""; $i = 0;

	foreach ($p_arr as $this) { 

 			$p_char = ( $i%3==0 ? "r" : ( $i%3==1 ? "w" : "x" ) ); 
 			$perms .= ( $this=="1" ? $p_char : "-" ) . ( $i%3==2 ? " " : "" );
 			$i++;
	}

	return $perms;
}

Hope that helps,
Matt

[feldon23]

Permissions on PHP are extremely annoying.

PHP is running as a "guest" on your server. Directories it creates will be owned by "nobody", "apache", "httpd", or in my case "99".

You have two choices.

One, login as root and add 99 and your user account to the same group and chmod the file/directory so owner and group have full access (774).

Two, after uploading/creating files/directories in your PHP script, have your PHP script chmod them to a permission that you have sufficient control under FTP.

[Alexandros]

To change permissions to files and folders to my remote server I use a program called SmartFTP. It is freeware.

Basically if you set permissions CHMOD to 0777 this gives all the permissions to others to access modify and delete the particular files or folders.

[Ignus_Fatuus]

Thanks alot for these answers, they really helped me on my way 🙂