OK I find out how to extract core dump (sorry), hope this will help you.
gdb /usr/lib/dovecot/auth /var/core/core.28304
GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from /usr/lib/dovecot/auth...Reading symbols from /usr/lib/debug/.build-id/ba/4974feed8c926e0d6e8d26659c583048a500f4.debug...done.
done.
[New LWP 28304]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by dovecot/auth -w'. Program terminated with signal SIGABRT, Aborted. #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51 51 ../sysdeps/unix/sysv/linux/raise.c: Aucun fichier ou dossier de ce type. (gdb) bt full #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51 set = {__val = {0, 2319406792476865588, 3472328228581767026, 3472310704041635888, 3966017812923691066, 7148958857402934374, 7089904100555370544, 3472328519666906169, 3472310978869031456, 3467824696600506928, 3979267959132535352, 2314885638479426609, 2314885530818453536, 2314885530818453536, 3907004821653777455, 8461816663211521631}} pid = <optimized out> tid = <optimized out> #1 0x00007fdb930a642a in __GI_abort () at abort.c:89 save_stage = 2 act = {__sigaction_handler = {sa_handler = 0x7220303030373836, sa_sigaction = 0x7220303030373836}, sa_mask = {__val = {3472328295963438381, 4192904167887482928, 2314885531086893104, 2314885530818453536, 2314885530818453536, 8528445641706184736, 7378645557150114166, 3472336027269751652, 3774971303630941488, 8223625903104145462, 3472328295963457581, 4192904167887482928, 2314885531086893104, 2314885530818453536, 2314885530818453536, 140727898588176}}, sa_flags = 89, sa_restorer = 0x7ffdc467c410} sigs = {__val = {32, 0 <repeats 15 times>}} #2 0x00007fdb930e2c00 in __libc_message (do_abort=do_abort@entry=2, fmt=fmt@entry=0x7fdb931d7d98 "*** Error in %s': %s: 0x%s ***\n") at ../sysdeps/posix/libc_fatal.c:175
ap = {{gp_offset = 40, fp_offset = 0, overflow_arg_area = 0x7ffdc467c420, reg_save_area = 0x7ffdc467c3b0}}
fd = 2
on_2 = <optimized out>
list = <optimized out>
nlist = <optimized out>
cp = <optimized out>
written = <optimized out>
#3 0x00007fdb930e8fc6 in malloc_printerr (action=3, str=0x7fdb931d7ef0 "double free or corruption (fasttop)", ptr=<optimized out>, ar_ptr=<optimized out>) at malloc.c:5049
buf = "0000562c3664bf70"
cp = <optimized out>
ar_ptr = <optimized out>
ptr = <optimized out>
str = 0x7fdb931d7ef0 "double free or corruption (fasttop)"
action = 3
#4 0x00007fdb930e980e in _int_free (av=0x7fdb9340bb00 <main_arena>, p=0x562c3664bf60, have_lock=0) at malloc.c:3905
size = <optimized out>
fb = <optimized out>
nextchunk = <optimized out>
nextsize = <optimized out>
nextinuse = <optimized out>
prevsize = <optimized out>
bck = <optimized out>
fwd = <optimized out>
errstr = <optimized out>
locked = <optimized out>
__func__ = "_int_free"
#5 0x00007fdb923e978f in mysql_close (mysql=0x562c3662f9b0) at ./libmariadb/libmariadb/mariadb_lib.c:1939
No locals.
#6 0x0000562c3457868c in driver_sqlpool_disconnect (_db=0x562c3662ea80) at driver-sqlpool.c:590
conn__foreach_end = 0x562c3662f160
db = 0x562c3662ea80
conn = 0x562c3662f150
#7 0x0000562c3456e0b5 in db_sql_unref (_conn=0x562c36624ff0) at db-sql.c:128
conn = 0x562c3662e6b8
#8 0x0000562c345669d9 in userdb_deinit (userdb=0x562c36624fc8) at userdb.c:191
idx = 0
__func__ = "userdb_deinit"
#9 0x0000562c3454ac89 in auth_deinit (auth=0x562c36624d28) at auth.c:335
passdb = <optimized out>
userdb = 0x562c36624ee8
#10 auths_deinit () at auth.c:433
auth__foreach_end = 0x562c3662e628
auth = 0x562c3662e620
#11 0x0000562c34549800 in main_deinit () at main.c:271
l = <optimized out>
#12 main (argc=<optimized out>, argv=<optimized out>) at main.c:398
c = <optimized out>
gdb /usr/lib/dovecot/auth /var/core/core.28358
GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from /usr/lib/dovecot/auth...Reading symbols from /usr/lib/debug/.build-id/ba/4974feed8c926e0d6e8d26659c583048a500f4.debug...done.
done.
[New LWP 28358]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by dovecot/auth -w'. Program terminated with signal SIGABRT, Aborted. #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51 51 ../sysdeps/unix/sysv/linux/raise.c: Aucun fichier ou dossier de ce type. (gdb) bt full #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51 set = {__val = {0, 2319406792476930356, 3472328228581767026, 3472310704041635888, 3966017812923691066, 7149237033791664998, 4049692877103575088, 3472328519683486774, 3472310978869031456, 3467824696600506928, 3979267959132535352, 2314885638479426609, 2314885530818453536, 2314885530818453536, 3907004821653777455, 8461816663211521631}} pid = <optimized out> tid = <optimized out> #1 0x00007f3862db642a in __GI_abort () at abort.c:89 save_stage = 2 act = {__sigaction_handler = {sa_handler = 0x7220303030383264, sa_sigaction = 0x7220303030383264}, sa_mask = {__val = {3472328295963438381, 4192904167887482928, 2314885531086893104, 2314885530818453536, 2314885530818453536, 8528445641706184736, 7378645557150114166, 3472337101783131493, 3559362570982206768, 8223625903106765412, 3472328295963457581, 4192904167887482928, 2314885531086893104, 2314885530818453536, 2314885530818453536, 140732686461920}}, sa_flags = 89, sa_restorer = 0x7ffee1c8ebe0} sigs = {__val = {32, 0 <repeats 15 times>}} #2 0x00007f3862df2c00 in __libc_message (do_abort=do_abort@entry=2, fmt=fmt@entry=0x7f3862ee7d98 "*** Error in %s': %s: 0x%s ***\n") at ../sysdeps/posix/libc_fatal.c:175
ap = {{gp_offset = 40, fp_offset = 0, overflow_arg_area = 0x7ffee1c8ebf0, reg_save_area = 0x7ffee1c8eb80}}
fd = 2
on_2 = <optimized out>
list = <optimized out>
nlist = <optimized out>
cp = <optimized out>
written = <optimized out>
#3 0x00007f3862df8fc6 in malloc_printerr (action=3, str=0x7f3862ee7ef0 "double free or corruption (fasttop)", ptr=<optimized out>, ar_ptr=<optimized out>) at malloc.c:5049
buf = "00005612cfa7ff70"
cp = <optimized out>
ar_ptr = <optimized out>
ptr = <optimized out>
str = 0x7f3862ee7ef0 "double free or corruption (fasttop)"
action = 3
#4 0x00007f3862df980e in _int_free (av=0x7f386311bb00 <main_arena>, p=0x5612cfa7ff60, have_lock=0) at malloc.c:3905
size = <optimized out>
fb = <optimized out>
nextchunk = <optimized out>
nextsize = <optimized out>
nextinuse = <optimized out>
prevsize = <optimized out>
bck = <optimized out>
fwd = <optimized out>
errstr = <optimized out>
locked = <optimized out>
__func__ = "_int_free"
#5 0x00007f38620f978f in mysql_close (mysql=0x5612cfa639b0) at ./libmariadb/libmariadb/mariadb_lib.c:1939
No locals.
#6 0x00005612ce45668c in driver_sqlpool_disconnect (_db=0x5612cfa62a80) at driver-sqlpool.c:590
conn__foreach_end = 0x5612cfa63160
db = 0x5612cfa62a80
conn = 0x5612cfa63150
#7 0x00005612ce44c0b5 in db_sql_unref (_conn=0x5612cfa58ff0) at db-sql.c:128
conn = 0x5612cfa626b8
#8 0x00005612ce4449d9 in userdb_deinit (userdb=0x5612cfa58fc8) at userdb.c:191
idx = 0
__func__ = "userdb_deinit"
#9 0x00005612ce428c89 in auth_deinit (auth=0x5612cfa58d28) at auth.c:335
passdb = <optimized out>
userdb = 0x5612cfa58ee8
#10 auths_deinit () at auth.c:433
auth__foreach_end = 0x5612cfa62628
auth = 0x5612cfa62620
#11 0x00005612ce427800 in main_deinit () at main.c:271
l = <optimized out>
#12 main (argc=<optimized out>, argv=<optimized out>) at main.c:398
c = <optimized out>
gdb /usr/lib/dovecot/auth /var/core/core.28359 GNU gdb (Debian 7.12-6) 7.12.0.20161007-git Copyright (C) 2016 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from /usr/lib/dovecot/auth...Reading symbols from /usr/lib/debug/.build-id/ba/4974feed8c926e0d6e8d26659c583048a500f4.debug...done. done. [New LWP 28359] [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". Core was generated by `dovecot/auth -w'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x00007f86d33a668b in mysql_close (mysql=0x55dcd013f9b0) at ./libmariadb/libmariadb/mariadb_lib.c:1919 1919 ./libmariadb/libmariadb/mariadb_lib.c: Aucun fichier ou dossier de ce type. (gdb) bt full #0 0x00007f86d33a668b in mysql_close (mysql=0x55dcd013f9b0) at ./libmariadb/libmariadb/mariadb_lib.c:1919 p = 0x55dcd0150c30 #1 0x000055dccf26e68c in driver_sqlpool_disconnect (_db=0x55dcd013ea80) at driver-sqlpool.c:590 conn__foreach_end = 0x55dcd013f160 db = 0x55dcd013ea80 conn = 0x55dcd013f150 #2 0x000055dccf2640b5 in db_sql_unref (_conn=0x55dcd0134ff0) at db-sql.c:128 conn = 0x55dcd013e6b8 #3 0x000055dccf25c9d9 in userdb_deinit (userdb=0x55dcd0134fc8) at userdb.c:191 idx = 0 __func__ = "userdb_deinit" #4 0x000055dccf240c89 in auth_deinit (auth=0x55dcd0134d28) at auth.c:335 passdb = <optimized out> userdb = 0x55dcd0134ee8 #5 auths_deinit () at auth.c:433 auth__foreach_end = 0x55dcd013e628 auth = 0x55dcd013e620 #6 0x000055dccf23f800 in main_deinit () at main.c:271 l = <optimized out> #7 main (argc=<optimized out>, argv=<optimized out>) at main.c:398 c = <optimized out>
gdb /usr/lib/dovecot/auth /var/core/core.28361 GNU gdb (Debian 7.12-6) 7.12.0.20161007-git Copyright (C) 2016 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from /usr/lib/dovecot/auth...Reading symbols from /usr/lib/debug/.build-id/ba/4974feed8c926e0d6e8d26659c583048a500f4.debug...done. done. [New LWP 28361] [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". Core was generated by `dovecot/auth -w'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x00007fd3d997a68b in mysql_close (mysql=0x563ef440a9b0) at ./libmariadb/libmariadb/mariadb_lib.c:1919 1919 ./libmariadb/libmariadb/mariadb_lib.c: Aucun fichier ou dossier de ce type. (gdb) bt full #0 0x00007fd3d997a68b in mysql_close (mysql=0x563ef440a9b0) at ./libmariadb/libmariadb/mariadb_lib.c:1919 p = 0x563ef441bc30 #1 0x0000563ef233168c in driver_sqlpool_disconnect (_db=0x563ef4409a80) at driver-sqlpool.c:590 conn__foreach_end = 0x563ef440a160 db = 0x563ef4409a80 conn = 0x563ef440a150 #2 0x0000563ef23270b5 in db_sql_unref (_conn=0x563ef43ffff0) at db-sql.c:128 conn = 0x563ef44096b8 #3 0x0000563ef231f9d9 in userdb_deinit (userdb=0x563ef43fffc8) at userdb.c:191 idx = 0 __func__ = "userdb_deinit" #4 0x0000563ef2303c89 in auth_deinit (auth=0x563ef43ffd28) at auth.c:335 passdb = <optimized out> userdb = 0x563ef43ffee8 #5 auths_deinit () at auth.c:433 auth__foreach_end = 0x563ef4409628 auth = 0x563ef4409620 #6 0x0000563ef2302800 in main_deinit () at main.c:271 l = <optimized out> #7 main (argc=<optimized out>, argv=<optimized out>) at main.c:398 c = <optimized out>