Commented by: @AlexPeshkoff

What I use is definitely not KUbuntu but... I can not reproduce an issue:

bash-2.05b#⁠ ./isql
Use CONNECT or CREATE DATABASE to specify a database
SQL> ^Dbash-2.05b#⁠ ./isql -user SYSDBA employee
Database: employee, User: SYSDBA
SQL> CREATE USER MYADMIN PASSWORD '123' GRANT ADMIN ROLE;
bash-2.05b#⁠ ./isql -user MYADMIN employee
Database: employee, User: MYADMIN
SQL> CREATE DATABASE '/tmp/MYDB.FDB' PAGE_SIZE 4096;
Commit current transaction (y/n)?y
Committing.
SQL> QUIT;
bash-2.05b#⁠ ./isql -z
ISQL Version: LI-V3.0.1.32609 Firebird 3.0
Use CONNECT or CREATE DATABASE to specify a database
SQL> ^Dbash-2.05b#⁠

Take into an account that _such_ bugs are typically caught by our regression tests.
BTW - why use i686 on 64-bit system?

Please provide stack traces for all threads - may be this helps.

Commented by: Gabor Boros (gaborboros)

I use amd64 build for 64bit certainly, i686 is just a mistype, corrected it.

How can I create a stack trace?

Commented by: @AlexPeshkoff

As far as I can see you already have core dump:
> Segmentation fault (core dumped)
A place and name of core dump file should be found in ubuntu docs, as far as I know it may be rather exotic on ubuntu.

Install appropriate debuginfo file - just untar it in the "/" of your FS.

Now you may use gdb to analyze coredump:
#⁠ gdb /opt/firebird/bin/isql <core-file-name>
On (gdb) prombt do: thread apply all bt
Send output here.

Commented by: Gabor Boros (gaborboros)

I hope this is what you want:

[New LWP 6375]
[New LWP 6369]
[New LWP 6368]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./isql -user MYADMIN employee'.
Program terminated with signal SIGSEGV, Segmentation fault.
#⁠0 0x00007f0dae810719 in ?? ()
(gdb) thread apply all bt

Thread 3 (Thread 0x7f0db20207c0 (LWP 6368)):
#⁠0 0x00007f0db04d12a7 in sched_yield () at ../sysdeps/unix/syscall-template.S:81
#⁠1 0x00007f0db1add445 in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠2 0x00007f0db1addfbc in fb_shutdown () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠3 0x00007f0db1aa0a87 in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠4 0x00007f0db1aa7a89 in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠5 0x00007f0dad6b51db in ?? () from /opt/firebird/plugins/libfbtrace.so
#⁠6 0x00007f0dad6b8f94 in ?? () from /opt/firebird/plugins/libfbtrace.so
#⁠7 0x00007f0dad6b919c in ?? () from /opt/firebird/plugins/libfbtrace.so
#⁠8 0x00007f0db04421a9 in __run_exit_handlers (status=0, listp=0x7f0db07c46c8 <__exit_funcs>, run_list_atexit=run_list_atexit@entry=true) at exit.c:82
#⁠9 0x00007f0db04421f5 in __GI_exit (status=<optimized out>) at exit.c:104
#⁠10 0x00007f0db0427f4c in __libc_start_main (main=0x4314a0 <main(int, char**)>, argc=4, argv=0x7ffcbc2ad958, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffcbc2ad948) at libc-start.c:321
#⁠11 0x0000000000409d69 in _start () at ../sysdeps/x86_64/elf/start.S:113

Thread 2 (Thread 0x7f0daff13700 (LWP 6369)):
#⁠0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
#⁠1 0x00007f0db1b79b32 in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠2 0x00007f0db1ade3b5 in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠3 0x00007f0db1b4758f in ?? () from /opt/firebird/bin/../lib/libfbclient.so.2
#⁠4 0x00007f0db07d3184 in start_thread (arg=0x7f0daff13700) at pthread_create.c:312
#⁠5 0x00007f0db050037d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

Thread 1 (Thread 0x7f0da9ff5700 (LWP 6375)):
#⁠0 0x00007f0dae810719 in ?? ()
#⁠1 0x00007f0da9ff4dc0 in ?? ()
#⁠2 0x00007f0dae819e3f in ?? ()
#⁠3 0x0000000000000000 in ?? ()