http://www.destructor.de/firebird/gbak.htm

update rdb$database set RDB$CHARACTER_SET_NAME='WIN1251'

change SQL dialect:
gfix -sql_dialect 3 -user marto -password sv  e:\OpenHouse\DATA_CDB.fdb

gsec -user sysdba -password masterkey -add marto -pw sv

Examples
A regular Backup
gbak -v -t -user SYSDBA -password "masterkey" dbserver:/db/warehouse.fdb c:\backups\warehouse.fbk

Backup with output to a logfile 
del c:\backups\warehouse.log
gbak -v -t -user SYSDBA -password masterkey -y c:\backups\warehouse.log dbserver:/db/warehouse.fdb c:\backups\warehouse.fbk

A regular Restore 
gbak -c -v -user SYSDBA -password masterkey c:\backups\warehouse.fbk dbserver:/db/warehouse2.fdb

Restore to an already existing database (Firebird 1.0, 1.5)
gbak -c -r -v -user SYSDBA -password masterkey c:\backups\warehouse.fbk dbserver:/db/warehouse.fdb

Restore to an already existing database (Firebird 2.x)
gbak -r o -v -user SYSDBA -password masterkey c:\backups\warehouse.fbk dbserver:/db/warehouse.fdb

Create a read-only database
gbak -c -v -mode read_only -use_all_space -user SYSDBA -password masterkey c:\backups\warehouse.fbk c:\files\warehousedb.fdb