after upgrade gdb won't attach to process

In Maverick Meerkat (10.10) Ubuntu introduced a patch to disallow ptracing of non-child processes by non-root users - ie. only a process which is a parent of another process can ptrace it for normal users - whilst root can still ptrace every process. Hence why you can use gdb to attach via sudo still.

You can temporarily disable this restriction (and revert to the old behaviour allowing your user to ptrace (gdb) any of their other processes) by doing:

echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

To permanently allow it edit /etc/sysctl.d/10-ptrace.conf and change the line:

kernel.yama.ptrace_scope = 1

To read:

kernel.yama.ptrace_scope = 0

For some background on why this change was made, see the Ubuntu wiki.

If you prefer to leave /proc/sys/kernel/yama/ptrace_scope set to its default value of 1, then as a workaround you could consider using gdb to run the program you want to debug. You can then bring up the debugger simply by pressing ^C. For example, to debug to the (boring) program sleep 60, do the following:

$ gdb -q sleep -ex 'run 60'

Here is a complete example.

$ gdb -q sleep -ex 'run 60'
Reading symbols from sleep...(no debugging symbols found)...done.
Starting program: /bin/sleep 60
^C
Program received signal SIGINT, Interrupt.
0x00007ffff7ad5d60 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:81
81      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) backtrace
#0  0x00007ffff7ad5d60 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:81
#1  0x0000000000403cd7 in ?? ()
#2  0x0000000000403b88 in ?? ()
#3  0x00000000004016c9 in ?? ()
#4  0x00007ffff7a35ec5 in __libc_start_main (main=0x401540, argc=2, argv=0x7fffffffea08, init=<optimized out>, 
    fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffe9f8) at libc-start.c:287
#5  0x00000000004017d5 in ?? ()
(gdb) continue
Continuing.
[Inferior 1 (process 3531) exited normally]
(gdb) quit

Since /bin/sleep was (unsurprisingly) compiled without debugging information, the above backtrace contains minimal information.