When try manual boot
Like:

grub> ls /boot/vmlinuz-3.10.0-
vmlinuz-3.10.0-123.el7.x86_64 vmlinuz-3.10.0-693.el7.x86_64
grub> set root=(hd0,msdos1)
grub> linux16 /boot/vmlinuz-3.10.0-123.el7.x86_64 root=/dev/sda1 rw init=/bin/bash
grub> initrd /boot/initramfs-3.10.0-123.el7.x86_64.img
grub> boot

It open bash shall 4.2
like:

bash-4.2# systemctl start systemd.tergate
dbus connection failed
when try