This is a very simple and most useful tutorial about changing user and group permissions of folders and files or entire folder recursively. When you transfer files with SCP and restore them on new server it is required to update their user and group permission otherwise your users can not use or sometimes access these files as permissions of fies are set as root by default and your virtual host have no permission to make changes in these files.
The Unix files access is controlled. There are three types of access (permissions):
Each file belongs to a specific user and group (ownership).
Access to the files is controlled by user, group, and what is called other/everyone permission bits and is usually set using a numerical value. For example, 644 as permission bit will result in:
Owner / User Group Other/ Everyone
6 4 4
Each number represents the access level and it can be from 0 to 7. The access level, depending on the number is as follows:
0 – no access to the file whatsoever
1 – execute permissions only
2 – write permissions only
3 – write and execute permissions
4 – read permissions only
5 – read and execute permissions
6 – read and write permissions
7 – read, write and execute permissions (full permissions)
Thus the above 644 permissions example will look like this:
Owner / User – Read and Write
Group – Read and Write
Other/ Everyone – Read only
To allow a script to be executed and read by everyone but the only one who can write in it is your user, you would need to set 755 as permissions:
Owner / User
7 – Full permissions
5 – read and execute
5 – read and execute
Changing the permissions to 700 will make the file visible only for your username and no one else and setting it to 444 will allow only the file creator to modify it.
The command you need to issue to actually change the permissions is called ‘chmod’ and it generally looks like this:
chmod 755 configuration.php
The above example changes the permissions of configuration.php file and sets them to 755. You can recursively change the permissions of all folders and files using the recursive argument:
chmod -R 755 *
This will modify the permissions of all files in the current folder and set them to 755.
You might wonder what the above user/group values are. These two settings are the actual ownership flags for a file or a folder. Each file has a primary user that owns it and a group assigned to it. To change those values, a special command exists — ‘chown’. Its syntax is very easy:
chown user:group file
chown user:itshacked configuration.php
The above line will set the owner of the file to ‘user’ and the group to ‘itshacked’.
Changing ownership recursively is also permitted and the flag (naturally) is -R:
chown -R user:itshacked *
I am collecting some references for Math behind the file permission and will publish it soon after completion.