to backup, I used
gbak -g -v -b -z -l -t -user sysdba -pass xxxxxxx
/usr/interbase/database/ipuc.gdb ipuc_b.gbk

to restore

gbak -v -r -t /usr/local/firebird/backup/ipuc_b.gbk
/usr/local/firebird/database/ipuc.fdb

then, that's errors occurs

svrsisnet# ./do_restore.sh
gbak: opened file /usr/local/firebird/backup/ipuc_b.gbk
gbak: transportable backup -- data in XDR format
gbak: backup file is compressed
gbak: created database /usr/local/firebird/database/ipuc.fdb,
page_size 1024
bytes
gbak: ERROR: invalid database handle (no active connection)
gbak: Exiting before completion due to errors
gbak: ERROR: invalid database handle (no active connection)