what you will need is a NULL-MODEM CABLE (with all the twist an wirering)

Linux Debian picocom / minicom settings:

apt-get update;
apt-get install picocom; # install picocom
sudo bash; # become root

dmesg | egrep --color 'serial|ttyS'; # what serial COM Ports are there and what is their settings

stty < /dev/ttyS0; # check settings of COM1
stty < /dev/ttyS1; # check settings of COM2

picocom /dev/ttyS1 -b 57600;# start picocom

# if your com port is working you should be greeted with a:

mguard login: root
Password: root
Innominate mGuard
Copyright (C) 2001-2014 Innominate Security Technologies and others

NOTE: Any modification of the software will void your support.
Please use the 'gaiconfig' command for configuration changes.
The usage of this mGuard security appliance is reserved to
authorized staff only. Any intrusion and its attempt without
permission is illegal and strictly prohibited.

BusyBox v1.12.0 (2015-04-13 06:56:28 CEST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

# to exit picocom hit Strl/Ctrl+a then Strl/Ctrl+x

if you enter „reboot“ „halt“ or „init 0“ it will actually do a reboot, not shutdown which looks like…

U-Boot 2012.07 (Apr 13 2015 - 06:57:27)MPC83XX

Reset Status:

CPU:   e300c3, MPC8313E, Rev: 2.1 at 330 MHz, CSB: 165 MHz
Board: Freescale MPC8313 MGUARD2
I2C:   ready
DRAM:  128 MiB (DDR2, 16-bit, ECC off, 330 MHz)
NAND:  Manufacturer: 0x2c, Chip: 0xf1 (Micron NAND 128MiB 3,3V 8-bit) 128 MiB
## Switch baudrate to 57600 bps andpress ENTER ...
Booting filesystem: 1: rootfs1
In:    serial
Out:   serial
Err:   serial
Device id: 0x3401
Net:   Check for empty flash: 0x7f00000 @ 0x100000
NAND not empty @ 00100000
No ethernet found.
Hit any key to stop autoboot:  0
Creating 1 MTD partitions on "nand0":
0x000000100000-0x000008000000 : "mtd=1"
UBI: attaching mtd1 to ubi0
UBI: physical eraseblock size:   131072 bytes (128 KiB)
UBI: logical eraseblock size:    129024 bytes
UBI: smallest flash I/O unit:    2048
UBI: sub-page size:              512
UBI: VID header offset:          512 (aligned 512)
UBI: data offset:                2048
UBI: attached mtd1 to ubi0
UBI: MTD device name:            "mtd=1"
UBI: MTD device size:            127 MiB
UBI: number of good PEBs:        1012
UBI: number of bad PEBs:         4
UBI: max. allowed volumes:       128
UBI: wear-leveling threshold:    4096
UBI: number of internal volumes: 1
UBI: number of user volumes:     6
UBI: available PEBs:             0
UBI: total number of reserved PEBs: 1012
UBI: number of PEBs reserved for bad PEB handling: 10
UBI: max/mean erase counter: 84/11
UBIFS: mounted UBI device 0, volume 2, name "rootfs1"
UBIFS: mounted read-only
UBIFS: file system size:   32126976 bytes (31374 KiB, 30 MiB, 249 LEBs)
UBIFS: journal size:       9033728 bytes (8822 KiB, 8 MiB, 71 LEBs)
UBIFS: media format:       w4/r0 (latest is w4/r0)
UBIFS: default compressor: LZO
UBIFS: reserved for root:  0 bytes (0 KiB)

NAND read: device 0 offset 0x7c000, size 0x4000
 16384 bytes read: OK
Loading file 'vmlinuz' to addr 0x01000000 with size 1927662 (0x001d69ee)...
## Booting kernel from Legacy Image at 01000000 ...
   Image Name:   Linux-3.10.17-mguard-7.0.21
   Created:      2015-04-13   5:02:32 UTC
   Image Type:   PowerPC Linux Kernel Image (lzma compressed)
   Data Size:    1927598 Bytes = 1.8 MiB
   Load Address: 00000000
   Entry Point:  00000000
   Verifying Checksum ... OK
## Flattened Device Tree blob at 02000000
   Booting using the fdt blob at 0x02000000
   Uncompressing Kernel Image ... OK

Under Windows use putty: