Managing File/Folder Permissions and Ownership

The Unix files access is controlled. There are three types of access (permissions):

• read
• write
• execute

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 644

Each number represents the access level and it can be from 0 to 7.

Different access levels depending on the numbers:

• 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 only
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
Group - 5 - read and execute
Other/Everyone - 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 execute to actually change the permissions is called ‘chmod’ and its syntax looks like this:

chmod 755 file_name

The above example changes the permissions of the file_name 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:

chown user:group file

For example:

chown user:siteground file_name

The above line will set the owner of the file to ‘user’ and the group to ‘siteground’.

Changing ownership recursively is also permitted and the flag is -R:

chown -R user:siteground *