/auto/jacal/scripts/format.linux.refresh.4.pl is called. The first thing the script does is activate the ssh server daemon on the current machine. Then it runs the script rcclient.pl which talks to rcserv.pl on the Linux master machine. The rcserv.pl is a script on the Linux master which runs the script /auto/jacal/scripts/rsync.build.sh. rsync.build.sh uses the rsync utility to intelligently copy the local file-system to the machine being built. rsync.build.sh calls rsync multiples times with certain parameter designed to avoid overwriting configuration files that already exist.
The rsync utility is used because it compresses the files before transfer and it doesn't copy files that already exist (unless they're different of course). In addition, rsync allows ssh to be used to perform the transfer instead of rsh, so the transfer of files is encrypted.