Linux operative system (and generally all the *NIX systems) allows, at any time, to check, modify and assign special permissions to files and folders contained in the web space, accessing by ftp and using the CHMOD command (change the access mode of a file).
That way you can enable specific users (or group of users) to make only particular operations on a file or a folder.
Generally, users of *nix systems are divided into three categories:
1. OWNER: who created the file or the folders,
2. GROUP: a group of users whom you can assign the same permissions corresponding to a file or a folder to,
3. USER: all the other users.
The type of permission you can assign to different users is:
• reading (r=4): that is viewing the list of files present in the folder or the file content;
• writing (w=2): possibility of adding files to a folder or modifying the file content;
• executing (x=1): permission of executing the file.
In the FTP client you can specify the different permissions with a group of three digits: the position and the value of the digit determine both the type of permission assigned and the user to whom it is associated.
• the first three specify the type of permissions assigned to the owner;
• the second three specify the type of permissions assigned to the group ("owen")
• the third three specify the permission assigned to the other users.
Every digit corresponds to one or more types of permissions.
4= only reading permission (r--)
5= only reading + executing permission(r-x)
6= only reading +writing permission (rw-)
7= reading + writing + executing permission (rwx)
Therefore assign the 777 permission to a folder (rwx rwx rwx) means that:
The owner has got all the permissions: reading, writing, executing. As well as for the group and all the other users: they can also have reading, writing and executing permissions and therefore can access the folder or files, view and update them.
While, assign 644 permission to a file (rw- r-- r--) means that:
the owner has got reading and writing permissions, he can modify its content, but he cannot execute the script, while the group and the other users have got only writing permissions and they can only access the file and view its content, without modifying or executing it.
Generally, you can assign the permissions you want to files and folders inside Linux space, however considering the limits relating to the obligatory permissions to assign to some files and folders.