Re: making your system robust

[Yoshinori K. Okuji]

On Monday 28 June 2004 16:02, Robert Millan wrote:
> Uhm. I think it's quite hard to support all possible variations of
> menu.lst in a script that sets the proper setdefault options, while
> ensuring there's no collateral effect. Do you have a particular
> scheme in mind for modifying it from the script?

It's quite trivial for me. Here is an example to set up a menu.lst (not 
complete or not tested):

#! /bin/bash

# Arguments.
boot=$0

# Obtain the current entry number.
current=0
default=`grep ^default /boot/grub/menu.lst | sed -e 's/default  
*\(saved|[0-9]*\)/\1/'`
case "$default" in
saved)
  line=`head -1 /boot/grub/menu.lst`
  if echo $line | grep -q; then
    current=`echo $line | sed -e 's/^\([0-9][0-9]*\).*/\1/'`
  fi
  ;;
[0-9]*)
  current=$default
  ;;
esac

# Make a temporary file to set fallback and default correctly.
tmp=/tmp/menu.lst.$$
cat <<EOF >$tmp
default saved
fallback $current
EOF

in_entry=0
num=0
while read line; do
  if test $in_entry = 0; then
    # Skip default and fallback in the original.
    if cat $line | grep -q ^default; then
      :
    elif cat $line | grep -q ^fallback; then
      :
    elif cat $line | grep -q ^title; then
      in_entry=1
      echo $line >> $tmp
    else
      echo $line >> $tmp
    fi
  else
    # Count entries.
    if cat $line | grep -q ^title; then
      num=`expr $num + 1`
    fi
    # If this is the target entry, insert savedefault and ignore it in 
the original.
    if test $boot -eq $num; then
      if cat $line | grep -q ^title; then
        echo $line >> $tmp
        echo "savedefault fallback" >> $tmp
      elif cat $line | grep -q ^savedefault; then
        :
      else
        echo $line >> $tmp
      fi
    else
      echo $line >> $tmp
    fi
  fi
done < /boot/grub/menu.lst

# Finish.
mv -f $tmp /boot/grub/menu.lst
exit 0


Probably it is necessary to add more code, for example, because this 
does not take it into account that the user might run this script more 
than once. And, it is better to restore the original menu.lst at next 
boot time. Maybe using an init script.

Okuji