Linux Swap Space Mini-HOWTO

9. The swapinit.sh script

This shell script initializes the swap space on the partition. The code for signature detection has been repeated 6 times because many a times the signature is properly detected only on the second or the third try.

(Adapted from the original Swap-Space-HOWTO by H. Peter Anvin)

 
#!/bin/sh 
# 
# swapinit.sh - activate the swap partition 
# 
# written by Rahul U. Joshi 
# Verify and initialize swap space 
# 
 
echo -n 'Verifying swap space... ' 
 
loopcount=0 
 
# flag to indicate whether the partition has been activated or not 
activated=0 
 
# check for signatures 6 times before giving up 
while [ $loopcount -lt 6 ] 
  do 
 
  if [ "`/bin/dd 2>/dev/null if=/dev/winswap bs=1 count=10  skip=4086`" = 'SWAP-SPACE' ]; then 
    echo "Linux signature found, iteration $loopcount" 
    echo "Activating swap partitions"  
    swapon /dev/winswap 
    activated=1 
    break 
 
  elif [ "`/bin/dd 2>/dev/null if=/dev/winswap bs=1 count=11 skip=43`" = 'SWAP SPACE ' ]; then    
    echo "DOS signature found, iteration $loopcount" 
    echo "Making swap partition"   
    mkswap /dev/winswap YYYYY 
    echo "Activating swap partitions"  
    swapon /dev/winswap 
    activated=1 
    break 
 
  else    
   let loopcount=loopcount+1 
  fi   
 
  done 
 
 
if [ $activated -ne 1 ] ; then 
  echo "Swap signature not found after $loopcount tries" 
  echo "No swapping partitions activated" 
  exit 1 
fi