create the new file with your desired size (usually swap file is as big as RAM)
Attention: dd count parameter means number of blocks (thus 4GB = 4 million blocks with blocksize 1K)
SWAPFILE=/home/swap.file
SWAPMEGABYTES=4096
#create the new file
BLOCKCOUNT=$(($SWAPMEGABYTES * 1024))
dd if=/dev/zero of=${SWAPFILE} bs=1024 count=${BLOCKCOUNT}
#format the file with swap file system:
mkswap ${SWAPFILE}
add the new file with type swap to fstab:
vi /etc/fstab
add new entry for swap file:
/path/to/swap.file none swap sw 0 0
remount fstab:
mount -a
activate swap for all entries in fstab:
swapon -a
show if everything worked well and swap space has changed:
free