Linux File Permissions

There are three type of users are available in Linux:
1) user
2) groups
3) Others

User: The username of the person who owns the file. By default, the user who creates the file will become its owner.

Group: The usergroup that owns the file. All users who belong into the group that owns the file will have the same access permissions to the file. This is useful if, for example, you have a project that requires a bunch of different users to be able to access certain files, while others can't. In that case, you'll add all the users into the same group, make sure the required files are owned by that group, and set the file's group permissions accordingly.

Other: A user who isn't the owner of the file and doesn't belong in the same group the file does. In other words, if you set a permission for the "other" category, it will affect everyone else by default. For this reason, people often talk about setting the "world" permission bit when they mean setting the permissions for "other".

Three Types of Permissions:

• Read permission
• Write permission
• Execute permission

How to View the Permissions

ls -l <filename>

For example:

me@mytux: /home/writers$ ls -l
total 17
drwxr-xr-x 3 nana writers 80 2005-09-20 21:37 dir
-rw-r----- 1 nana writers 8187 2005-09-19 13:35 file
-rwxr-xr-x 1 nana writers 10348 2005-07-17 20:31 otherfile

Notations:

d = directory
- = regular file
l = symbolic link
s = Unix domain socket
p = named pipe
c = character device file
b = block device file
r = read permission
w = write permission
x = execute permission
- = no permission
4 = read (r)
2 = write (w)
1 = execute (x)
0 = no permission (-)