PermissionsEvery file on the system has associated with it a set of permissions. Permissions tell UNIX what can be done with that file and by whom. There are three things you can (or can't) do with a given file:
write (modify) it and
For any given ownership relation, we need three letters to specify access permissions: the first denotes read (r) access, the second denotes write (w) access and the third denotes execute (x) access.
We have three ownership relations: 'owner', 'group' and 'all' so we need a triplet for each, resulting in nine letters.
Lets try something in our command prompt with ls -l command.
From the above output, lets take an example. For logs, the permission of the folder is drwxr-xr-x. Lets break it down.
As previously said, it is 9 letter,
d - stands for directory
rwx - Read, write and execute permissions for the user
r-x - Read and execute permissions for the group
r-x - Read and execute permissions for all
Check here for CHMOD command and strange numbers