sftp is an ftp replacement that runs over an ssh tunnel. Two programs are included - sftp and sftpserv. When sftp is run and a host is connected to (either by running 'sftp remotehost' or 'open remotehost' from the sftp prompt), an ssh connection is initiated to the remote host, and sftpserv is run. So, sftpserv must be in your path on the remote host. Note that since sftpserv is run from ssh, no root privileges are necessary.