Linux File Permissions - wAlber47/Tech-Journal GitHub Wiki

Basics:

  • groupadd - adds a new group that can be applied to users.
  • useradd - adds a new user.
  • usermod -aG 'group-name' 'user' - adds a known user to a group.
  • ls -ld - shows information on a directory level.

Changing Permissions:

  • In order to change the permissions of a group, you should create a folder at root that you can use for that group. For example, when creating the management group, I first used groupadd management, then I used mkdir /management.
  • To Change the Group of a Directory or File:
    • chgrp 'group-name' 'location'
  • To Add Permissions to a Directory or File:
    • chmod 'perm-level'+'perm-type' 'location To Remove Permissions from a Directory or File:
    • chmod 'perm-level'-'perm-type' 'location'

Using Binary to Change Permissions:

  • Instead of using g+rwx or u+rwx, you can use chmod 777 or chmod 600 to change permissions.

  • Each permission type is related to a binary number made up of 3 bits:

    • read = r = 100 = 4
    • write = w = 010 = 2
    • execute = x = 001 = 1

  • Each column of the number is related to one specific group, (using 652 as an example):

    • '6' relates to the user column, and gives the read/write permissions to the file.
    • '5' relates to the group column, and gives the read/execute permissions to the file.
    • '2' relates to the other column, and gives the write permissions to the file.

  • When setting file permissions, you want to make sure that no one that doesn't require access to a file, has access. They should be fairly secure.