Where is the link command?

I am trying to line /dev/usb/ttyACM0 or /dev/modem to /dev/ttyACM0 since KPPP refuses recognize /dev/ttyACM0. The link command cannot be found, although man link shows it. Is there any other way to link the devices as mentioned above or to get KPPP to recognize /dev/ttyACM0? Art