Any reason you want to use 'grsync'? Trisquel has an excellent backup utility
(in "System settings"), which uses duplicity as a backend:
incremental backup (only backup what has not been backup-up yet);
compressed backup (faster and save space);
integrated with the file manager (you revert to any previous version of the
file/folder in about three clicks);
periodic backup (or a notification if the external drive is not plugged);
the oldest versions of the files are automatically removed if space is
missing;
very easy to use (choose where to backup and then use the graphical utility
with two buttons: "backup" and "restore");
possible encryption;
...
