partial linux troubleshooting march 22

[root@localhost ~]# history
    1  reboot
    2  cd /
    3  touch .autorelabel
    4  vim /etc/default/grub
    5  grub2-mkconfig -o /boot/grub2/grub.cfg
    6  reboot
    7  arp -a
    8  arp --help
    9  arp -d 192.168.29.149
   10  arp -a
   11  ping 192.168.29.149
   12  which mount
   13  mv /bin/mount /bin/tnuom
   14  cp /bin/false /bin/mount
   15  strace mount
   16  ls -l /usr/bin/mount /usr/bin/false
   17  mount --help
   18  false --help
   19  ls
   20  exit
   21  xxd -l 512 /dev/sda
   22  dd if=/dev/sda of=/boot/mbr_backup bs=512 count=1
   23  dd if=/dev/zero of=/dev/sda bs=512 count=1
   24  xxd -l 512 /dev/sda
   25  reboot
   26  history