fifth run, on a database WITH Level 0, Level 1, Level 2 and Level 3
nbackups
Be noticed: this script will ALWAYS makea level 3 backup,one after
another.

2007-09-29-18-07-13.
Resource id #2
SELECT RDB$BACKUP_LEVEL FROM RDB$BACKUP_HISTORY
level_0 primary nbackup found
level_1 nbackup file found
level_2 nbackup file found
level_3 nbackup file found

now begin to do the nbackups

the current directory:/usr/local/apache2/htdocs
change directory to /opt/firebird/bin
the current directory:/opt/firebird/bin
./nbackup -U sysdba -P masterkey -B 3 /home/myname/employee.fdb
/tmp/bak/employee_3-2007-09-29-18-07-13.nbk
nbackup result:

now change back to starting directory
the current directory:/usr/local/apache2/htdocs

system re-check if all nbackup files in position
file name: .
file name: employee_0-2007-09-29-17-58-14.nbk
file name: employee_3-2007-09-29-18-05-41.nbk
file name: employee_3-2007-09-29-18-07-13.nbk
file name: employee_2-2007-09-29-18-04-01.nbk
file name: employee_1-2007-09-29-18-01-50.nbk
file name: ..

nbackup file successful: /tmp/bak/employee_3-2007-09-29-18-07-13.nbk

confirm if nbackup is successful by re-connect the database
SELECT RDB$FILE_NAME FROM RDB$BACKUP_HISTORY
Resource id #2
/tmp/bak/employee_0-2007-09-29-17-58-14.nbk
/tmp/bak/employee_1-2007-09-29-18-01-50.nbk
/tmp/bak/employee_2-2007-09-29-18-04-01.nbk
/tmp/bak/employee_3-2007-09-29-18-05-41.nbk
/tmp/bak/employee_3-2007-09-29-18-07-13.nbk

disconnect from database OK !