File system settings

Submitted by admin@soz on Sat, 05/12/2018 - 16:26

This is how permissions are decoded
0 - No permission
1 - Can Execute (generally reserved for directories)
2 - Can Write
4 - Can Read

Adding 2 + 4 = 6, leads to permission for write and read.
7 means 1 + 2 + 4, basically execute, write and read.

Logically speaking, it is easy to infer that in most scenario there is not much difference between 6 and 7.

Another aspect in connection with permissions - is the file ownership.

This is how file ownerships are decoded

There are total 3 levels of ownership
U - user - also known as owner (the one who creates the file, automatically becomes the owner)
G - group - in linux a new user automatically defaults to the group by same name
O - other - any one who is not part of U or G, i simply describe this as rest of the world. 

Each file or directory typically have all these 3 levels. Any permissions that we give is seen with respect to this ownership hierarchy. It is in this order UGO

Read more:

For directories:-

r = list (read directory contents)
w = write
x = can access the directory (i.e., cd to the directory)

For files:-

r = read
w = write
x = execute

chmod human chmod numeric resulting permission
ugo=rwx 777 rwxrwxrwx
u-wx 470 r--rwx---
o+r 774 rwxrwxr--
g-wx,o+r 744 rwxr--r--
u-w,g-wx,o+r 544 r-xr--r--
g=,o=r 704 rwx---r--
a-wx 440 r--r-----