How to inspect process/core stack in gdb v6.8?

I used to run command line gdb debugger and use the "stack bt" command to inspect the stack of a core or a process.
Now I get this:

uqbar@g1s:~$ gdb --core=./core
GNU gdb 6.8-debian
Copyright (C) 2008 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".
(no debugging symbols found)
Core was generated by `python /usr/lib/glipper/glipper --oaf-activate-iid=OAFIID:Glipper_Factory --oaf'.
Program terminated with signal 6, Aborted.
[New process 7661]
#0 0x00007f5a5a620015 in ?? ()
(gdb) stack bt
Undefined command: "stack". Try "help".
(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.
Type "help all" for the list of all commands.
Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.
(gdb) help stack
Examining the stack.
The stack is made up of stack frames. Gdb assigns numbers to stack frames
counting from zero for the innermost (currently executing) frame.

At any time gdb identifies one frame as the "selected" frame.
Variable lookups are done with respect to the selected frame.
When the program being debugged stops, gdb selects the innermost frame.
The commands below can be used to select other frames by number or address.

List of commands:

backtrace -- Print backtrace of all stack frames
bt -- Print backtrace of all stack frames
down -- Select and print stack frame called by this one
frame -- Select and print a stack frame
return -- Make selected stack frame return to its caller
select-frame -- Select a stack frame without printing anything
up -- Select and print stack frame that called this one

Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.
(gdb) quit
uqbar@g1s:~$

Any suggestion?
Thanks.