# Step 1
$ sudo su -
...

# Step 2
# mkdir /var
mkdir: Failed to make directory "/var"; File exists
# mkfile 2048m /var/swap

# Step 3
# ls -l /var/swap
-rw-------   1 root     root     2147483648 Jul 16 11:42 /var/swap

# Step 4
# swap -a /var/swap
"/var/swap" is not valid for swapping.
It must be a block device or a regular file with the
"save user text on execution" bit set.

ls -l /directory/swap-file-name

ls -l /foo/16mswap    -rw------T   1 root     other    16777216 Dec 12 14:24 /foo/16mswap

chmod +t filename