make file swap.

mkfileswap.sh

#!/bin/bash
# N and BYTES may be followed by the following multiplicative suffixes:
# c =1, w =2, b =512, kB =1000, K =1024, MB =1000*1000, M =1024*1024

help(){
    echo "useage: `basename $0` -o full_path -b block_size(default 1K) -c block_count(default 2M)"
}

while getopts 'o:b:c:' OPT; do
    case $OPT in
        o)
            of="$OPTARG";;
        b)
            bs="$OPTARG";;
        c)
            count="$OPTARG";;
    esac
done
if [ -z "$of" ]; then
    help
    exit 1;
fi
if [ -z "$bs" ]; then
    bs="1K"
fi
if [ -z "$count" ]; then
    count="2M"
fi
echo "create swap file on: $of with bs:$bs count:$count"
dd if=/dev/zero of=$of bs=$bs count=$count
/sbin/mkswap $of
/sbin/swapon $of
echo "writing swapfile:$of to /etc/fatab."
echo "$of swap swap defaults 0 0" >> /etc/fstab