To see the activity on your Backup Server before executing a shutdown command, run sp_who on the Backup Server:
SYB_BACKUP...sp_who
spid status loginame hostname blk cmd ------ -------- -------- ---------- --- ---------------- 1 sleeping NULL NULL 0 CONNECT HANDLER 2 sleeping NULL NULL 0 DEFERRED HANDLER 3 runnable NULL NULL 0 SCHEDULER 4 runnable NULL NULL 0 SITE HANDLER 5 running sa heliotrope 0 NULL