How to repair a corrupted Firebird database

Even if we take great care, it may happen that a Firebird DB may be corrupted.
Here you can find a list of corruptions reasons.
In this post I describe a brief guide of how to repair a corrupt database using the command line tools (gfix and gbak).

NB: Please note that not all the corrupted database can be restored. It depends on the corruption level. At the end of this tutorial you can find some rescue alternatives.

Step 1: Check the database integrity

First of all you should stop the Firebird server and make a copy of the database files. Keep these files in a secure place until you are sure that the database is perfectly restored!

You can use the following command to check the db integrity:

gfix -v -f -user sysdba -password masterkey db_corrupt.gdb

params:
    -v -> validate
    -f -> full

This command will print a summary of validation errors.

Step 2: Fix the errors

Use the following command to mend the db:

gfix -mend -user sysdba -password masterkey db_corrupt.gdb

Note that this command do not fix the errors, but flags the problems to be fixed. The errors will be solved in the next backup/restore step.

Step 3: Backup the DB

Use the following command to backup the db:

gbak -b -v -ig -user sysdba -password masterkey db_corrupt.gdb db_corrupt.gbk

params:
    -b  -> backup
    -v  -> verbose
    -ig -> ignore checksums

Step 4: Restore the DB

Use the following command to restore the db:

gbak -c -v -user sysdba -password masterkey db_corrupt.gbk db_fixed.gdb

params:
    -c -> create new db
    -v -> verbose

Step 5: Re-check the DB

Repeat the command in step 1 to check the new db:

gfix -v -f -user sysdba -password masterkey db_fixed.gdb

Possible alternatives:

1. If the database has still problems you can try to repeat the procedure using -g options (switch off garbage collection) in step 3.
   So step 3 will be:

   gbak -b -v -ig -g -user sysdba -password masterkey db_corrupt.gdb db_corrupt.gbk
   

2. If the database has still problems you can try to use a tool like IBSurgeon Tools (but I have never used them!)
3. If the db is corrupted but you can access to the data, you can copy the data to a new db using FbCopy or IB-Pump.

Related Links:

How to repair a corrupt Firebird database (The Firebird FAQ)
How To Analyse and Repair a Corrupted Database (IBPhoenix)
How to repair a corrupt Firebird database? (IBSurgeon)