$ cd /
/$ ls
bin dev home initrd.img.old lib64 media opt root sbin sys usr vmlinuz
boot etc initrd.img lib lost+found mnt proc run srv tmp var vmlinuz.old
/$ cd //
//$ ls
bin dev home initrd.img.old lib64 media opt root sbin sys usr vmlinuz
boot etc initrd.img lib lost+found mnt proc run srv tmp var vmlinuz.old
//$ pwd
//
//$ cd ///
/$
/$ pwd
/
這是什麼詭計？什麼是//？