操作步骤：

1、修改/etc/default/grub

## Modify this line by leekwen
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"

## Modify this line by leekwen
GRUB_TERMINAL=serial

## Add this line by leekwen
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

2、运行update-grub命令

3、增加配置文件/etc/init.d/ttyS0.conf

leekwen@leekwen:/etc/default$ cat /etc/init/ttyS0.conf
# Add those lines
# ttyS0 - getty
#
# This service maintains a getty on ttyS0 from the point the system is
# started until it is shut down again.


start on stopped rc RUNLEVEL=[2345] and (
            not-container or
            container CONTAINER=lxc or
            container CONTAINER=lxc-libvirt)


stop on runlevel [!2345]


respawn
exec /sbin/getty -L 115200 ttyS0 vt100


# Add those lines End

参考地址：

https://help.ubuntu.com/community/SerialConsoleHowto

https://help.ubuntu.com/community/Grub2