How to take core dump of a running process

1)
Method-1

$ gdb --pid=26426
(gdb) gcore
Saved corefile core.26426
(gdb) detach

2)
Method-2

$gcore pid_of_running_process
$gcore pid_of_running_process -o core_dump_file

3)
Method-3

* You can send signals which has action=core to the running process to take core dump.

$kill [signal] [pid]
Example:
$kill -SIGQUIT process_id