Remote Serial Console HOWTO
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5.2. Configure Linux kernel using GRUB

Find each title entry in the GRUB configuration file. It will be followed by a kernel line. For example

title Red Hat Linux (2.4.9-21)
  root (hd0,0)
  kernel /vmlinuz-2.4.9-21 ro root=/dev/hda6
  initrd /initrd-2.4.9-21.img

Modify each of the kernel lines to append the parameters that inform the kernel to use a serial console.

Figure 5-5. Recommened kernel parameters, GRUB configuration

title Red Hat Linux (2.4.9-21)
  root (hd0,0)
  kernel /vmlinuz-2.4.9-21 ro root=/dev/hda6 console=tty0 console=ttyS0,9600n8
  initrd /initrd-2.4.9-21.img

As a complete example, Example 5-3 is a typical GRUB configuration from Red Hat Linux 7.2.

Example 5-3. Complete GRUB configuration, as installed by vendor

default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
password --md5 $1$wwmIq64O$2vofKBDL9vZKeJyaKwIeT.
title Red Hat Linux (2.4.9-21)
root (hd0,0)
  kernel /vmlinuz-2.4.9-21 ro root=/dev/hda6
  initrd /initrd-2.4.9-21.img

The modified configuration file is shown in Example 5-4.

Example 5-4. Complete GRUB configuration, modified for serial console

default=0
timeout=10
password --md5 $1$wwmIq64O$2vofKBDL9vZKeJyaKwIeT.
serial --unit=0 --speed=9600 --word=8 --parity=no --stop=1
terminal --timeout=10 serial console
title Red Hat Linux (2.4.9-21)
  root (hd0,0)
  kernel /vmlinuz-2.4.9-21 ro root=/dev/hda6 console=tty0 console=ttyS0,9600n8
  initrd /initrd-2.4.9-21.img
title Red Hat Linux (2.4.9-21) single user mode
  lock
  root (hd0,0)
  kernel /vmlinuz-2.4.9-21 ro root=/dev/hda6 console=tty0 console=ttyS0,9600n8 s
  initrd /initrd-2.4.9-21.img

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