Installing Firebird from archieve

See Firebird 2 Migration & Installation for details.

If you you have any installed Firebird on your system, remove it before moving on. For instance:

sudo apt-get remove firebird2.5-common firebird2.5-common-doc firebird2.5-dev firebird2.5-examples firebird2.5-server-common firebird2.5-super

http://www.firebirdsql.org/en/downloads/
It'll look like somewhat below:
October 04, 2011 FirebirdSS-2.5.1.26351-0.i686.tar.gz 6 MB Superserver, compressed tarball

Next operations need root access!
Unpack content of the archieve and start:

install.sh

Installation complete.

If you come across with system output like follows:

insserv: warning: script 'K20acpi-support' missing LSB tags and overrides
The script you are attempting to invoke has been converted to an Upstart
job, but lsb-header is not supported for Upstart jobs.
insserv: warning: script 'cryptdisks-udev' missing LSB tags and overrides
The script you are attempting to invoke has been converted to an Upstart
job, but lsb-header is not supported for Upstart jobs.
insserv: warning: script 'bridge-network-interface' missing LSB tags and overrides
The script you are attempting to invoke has been converted to an Upstart
job, but lsb-header is not supported for Upstart jobs.
...and so on

than you need to patch «insserv bug»:

1. get this file upstart-job.patch

   *** upstart-job.orig    2011-03-16 08:06:15.275456408 -0400
   --- upstart-job 2011-03-16 08:44:45.622968551 -0400
   ***************
   *** 65,70 ****
   --- 65,82 ----
         $ECHO "Upstart job, you may also use the $COMMAND(8) utility, e.g. $COMMAND $JOB"
         reload "$JOB"
         ;;
   + lsb-header)
   +     $ECHO "### BEGIN INIT INFO"
   +     $ECHO "# Provides:          $JOB"
   +     $ECHO "# Required-Start:"
   +     $ECHO "# Required-Stop:"
   +     $ECHO "# Should-Start:"
   +     $ECHO "# Should-Stop:"
   +     $ECHO "# Default-Start:"
   +     $ECHO "# Default-Stop:"
   +     $ECHO "# Short-Description: $JOB, converted to upstart."
   +     $ECHO "### END INIT INFO"
   +     ;;
     *)
         $ECHO
         $ECHO "The script you are attempting to invoke has been converted to an Upstart" 1>&2

2. execute commands:

   cd /lib/init
   patch < your_path/upstart-job.patch

3. finish installation:

   /sbin/insserv /etc/init.d/firebird

Finally you'll see something similar to this:

insserv: warning: script 'K20acpi-support' missing LSB tags and overrides
insserv: warning: current start runlevel(s) (0) of script `halt' overwrites defaults (empty).
insserv: warning: current start runlevel(s) (0 6) of script `cryptdisks-early' overwrites defaults (empty).
insserv: warning: script 'acpi-support' missing LSB tags and overrides
insserv: warning: current start runlevel(s) (0 6) of script `umountnfs.sh' overwrites defaults (empty).
insserv: warning: current start runlevel(s) (0 6) of script `networking' overwrites defaults (empty).
...and so on

 $cd /opt/firebird/bin
 $./isql -user sysdba -password <password>1

 SQL>connect localhost:employee.fdb /* this is an aliased path */

 SQL>select * from sales;
 SQL>select rdb$relation_name from rdb$relations;
 SQL>help;

 SQL>quit;