(require :your-system) doesn't load system but system exist in asdf standard directory ~/common-lisp/.
CL-USER> (require :your-system)
Don't know how to REQUIRE YOUR-SYSTEM.
[Condition of type SB-INT:EXTENSION-FAILURE]
~/common-lisp/log-simple/YOUR-SYSTEM.asdf:
(in-package :cl-user)
(defpackage log-simple-asd
(:use :cl :asdf))
(in-package :log-simple-asd)
(defsystem log-simple
...)