Linux

1. chmod

   - chmod 400 file - Read by owner
   - chmod 040 file - Read by group
   - chmod 004 file - Read by world
   
   - chmod 200 file - Write by owner
   - chmod 020 file - Write by group
   - chmod 002 file - Write by world
   
   - chmod 100 file - execute by owner
   - chmod 010 file - execute by group
   - chmod 001 file - execute by world
   
   - chmod 444 file - Allow read permission to owner and group and world
   - chmod 777 file - Allow everyone to read, write, and execute file