Each and every operating systemI support has a different utility to report on swap usage. On my Soalris hosts, I use the swap and vmstat utilities to check utilization:
$ swap -s
total: 36176k bytes allocated + 4672k reserved = 40848k used, 1189004k available
On Linux hosts, I use teh free and top utilities:
$ free
total used free shared buffers cached Mem: 2055340 1427696 627644 0 179124 876300 -/+ buffers/cache: 372272 1683068 Swap: 1004052 0 1004052
And on my OpenBSD servers, I use the swapctl and systat utilities:
$ swapctl -l
Device 512-blocks Used Avail Capacity Priority swap_device 262068 0 262068 0% 0
Oh how I wish there was an administrator tool naming standard. :)