I have enable core dump on my machine. Im using eAthena. See the result below
After gdb map-server core.30056
Loaded symbols for /lib/libnss_files.so.2
Core was generated by `./map-server_sql'.
Program terminated with signal 11, Segmentation fault.
#0 0x0815828a in unit_walktoxy_timer (tid=3600, tick=3997628630, id=2000484,
data=189) at unit.c:194
194 if( g->member[i].online && g->member[i].sd && sd->bl.m == g->member[i].sd->bl.m && check_distance_bl(&sd->bl, &g->member[i].sd->bl, 2) )
Then the next command is bt full. See the result
(gdb) bt full
#0 0x0815828a in unit_walktoxy_timer (tid=3600, tick=3997628630, id=2000484,
data=189) at unit.c:194
skill = <value optimized out>
strvit = 65536
agidex = 0
i = 0
x = <value optimized out>
y = <value optimized out>
dx = 1
dy = <value optimized out>
bl = 0xd3ccf00
sd = 0xd3ccf00
md = 0x0
ud = 0xd3ccf18
#1 0x081675d9 in do_timer (tick=3997628644) at timer.c:371
tid = 3600
diff = -14
__FUNCTION__ = "do_timer"
#2 0x08164a1e in main (argc=1, argv=0xbfd731d4) at core.c:261
next = <value optimized out>