首先用-g选项编译程序，然后用
ulimit -c unlimited
打开core文件限制
to make the changes permanent, add the following line to /etc/sysctl.conf:
kernel.core_pattern = core.%e.%p
sysctl is a similar tool to ulimit: It allows to configure kernel
parameters at runtime. If you wish to keep settings persistent across
reboots you should edit /etc/sysctl.conf - be aware that wrong settings
may break things in unforeseen ways.
用/proc/sys/kernel/core_pattern控制core文件产生的地方
在测试站上
root: cat /proc/sys/kernel/corepattern
/tmp/core.%p%e
也就是说，所有core文件都在/tmp文件夹，文件名是
core.pid_execFileName
这时，启动任何程序，只要是非正常退出，都会产生一个core文件
echo "/tmp/core-%e-%p-%t" > core_pattern
将会控制所产生的core文件会存放到/tmp目录下，产生的文件名为core-命令名-pid-时间戳
以下是参数列表:
%p - insert pid into filename 添加pid
%u - insert current uid into filename 添加当前uid
%g - insert current gid into filename 添加当前gid
%s - insert signal that caused the coredump into the filename 添加导致产生core的信号
%t - insert UNIX time that the coredump occurred into filename 添加core文件生成时的unix时间
%h - insert hostname where the coredump happened into filename 添加主机名
%e - insert coredumping executable name into filename 添加命令名
然后用
gdb -f execfile -c corefile打开core文件，比如
gdb -c /tmp/core.24281_fweb -f /home/bbs/bbshome/httpd/fweb
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This GDB was configured as "i386-linux"…
Core was generated by `/home/bbs/bbshome/httpd/fweb’.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /usr/local/lib/libglib-2.0.so.0…done.
Loaded symbols for /usr/local/lib/libglib-2.0.so.0
Reading symbols from /usr/local/lib/libfcgi.so.0…done.
Loaded symbols for /usr/local/lib/libfcgi.so.0
Reading symbols from /lib/libdl.so.2…done.
Loaded symbols for /lib/libdl.so.2
Reading symbols from /lib/libc.so.6…done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/libnsl.so.1…done.
Loaded symbols for /lib/libnsl.so.1
Reading symbols from /lib/ld-linux.so.2…done.
Loaded symbols for /lib/ld-linux.so.2
Reading symbols from /home/bbs/bbshome/httpd/pages/bbsqry.so…done.
Loaded symbols for /home/bbs/bbshome/httpd/pages/bbsqry.so
Reading symbols from /home/bbs/bbshome/httpd/pages/bbsgetmsg.so…done.
Loaded symbols for /home/bbs/bbshome/httpd/pages/bbsgetmsg.so
Reading symbols from /home/bbs/bbshome/httpd/pages/bbslogin.so…done.
Loaded symbols for /home/bbs/bbshome/httpd/pages/bbslogin.so
#0 FCGI_fprintf (fp=0x0, format=0x40e9929e "%d") at fcgi_stdio.c:602
/root/fcgi-2.4.0/libfcgi/fcgi_stdio.c:602:15672:beg:0x400a1850
这个时候，你可以看是哪一步让进程死掉，比如先用
(gdb) backtrace
#0 FCGI_fprintf (fp=0x0, format=0x40e9929e "%d") at fcgi_stdio.c:602
#1 0x40e990ad in check_login_limit (x=0x805d5a0) at bbslogin.c:303
#2 0x40e988d5 in bbslogin_main () at bbslogin.c:127
#3 0x0804ca1c in do_invoke (p=0x8087408) at module.c:162
#4 0x0804ca80 in invoke_module (name=0x8083d59 "bbslogin") at module.c:192
#5 0x0804cb70 in process_request () at dispatcher.c:44
#6 0x0804cbf5 in cgiMain () at dispatcher.c:82
#7 0x0804cfb5 in serv_request () at cgic.c:322
#8 0x08050ae3 in main () at main.c:44
打印frames，然后用
(gdb) frame 1
#1 0x40e990ad in check_login_limit (x=0x805d5a0) at bbslogin.c:303
/home/jawahh/bbs/fweb/pages/bbslogin.c:303:6735:beg:0x40e990ad
选择你要看的frame，现在选择了#1 frame，然后就可以用如
(gdb) info locals
fp = (FCGI_FILE ) 0x0
filename = "home/C/clickbeetle/logincheck 05b診001 塞"
num = 0
察看本地变量
(gdb) list
298 sethomefile(filename, x->userid, "logincheck");
299 if (!file_exist(filename)
300 || abs(file_time(filename) - time(0)) > 86400)
301 {
302 fp = fopen(filename, "w");
303 fprintf(fp, "%d", x->numlogins);
304 fclose(fp);
305 return;
306 }
307 fp = fopen(filename, "r");
察看程序代码
(gdb) p fp
$5 = (FCGI_FILE ) 0x0
察看变量
等等等等很多方法，这样调试会简单多