I am not sure about 9.1, but on 9.7 I issue this command after restoring to the catalog node:
db2_all "db2 restore database sample from /stage/db2inst1/backup/SAMPLE taken at 20091012201205 without prompting"
Then:
db2 "rollforward db sample to 2009-10-12-20.12.10.000000 on all dbpartitionnums and stop"
This assumes that the backup path is /stage/db2inst1/backup/SAMPLE and it exists on all physical servers (in case you have more than one). If you are storing the backups under a "NODEnnnn" directory, then there is another thread about how to wild card that in the restore command.