I'm trying install firebird 2.5.x x86 on debian 10/ubuntu 18. When run install, I got

Extracting install data
Please enter new password for SYSDBA user: masterkey
./scripts/postinstall.sh: 114: ./scripts/postinstall.sh: /opt/firebird/bin/gsec: not found

ls -la  /opt/firebird/bin/gsec
-rwxr-xr-x 1 root root 297716 lut 14  2017 /opt/firebird/bin/gsec

What can I do to fix it?

"Not found" can mean some of the libraries it needs are missing. What do you get from the commands:

file /opt/firebird/bin/gsec

ldd /opt/firebird/bin/gsec

I have built a package of Firebird 2.5.8 for Debian 9/10. I prefer to run from packages than installing software directly like this.

Hamish