For example:

$ mongod --dbpath /mnt/rs/ --dur | tee rs.log
Wed Mar 9 19:49:55 [initandlisten] MongoDB starting : pid=6542 port=27017 dbpath=/mnt/rs/ 64-bit

• • NOTE: This is a development version (1.9.0-pre-) of MongoDB.
  • Not recommended for production.

Wed Mar 9 19:49:55 [initandlisten] db version v1.9.0-pre-, pdfile version 4.5
Wed Mar 9 19:49:55 [initandlisten] git version: afcf141e33a7d48ac396ea53125d0d8d71a33af7
Wed Mar 9 19:49:55 [initandlisten] build sys info: Linux bs-linux64.10gen.cc 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20 17:48:28 EST 2009 x86_64 BOOST_LIB_VERSION=1_41
Wed Mar 9 19:49:55 [initandlisten] journal dir=/mnt/rs/journal
Wed Mar 9 19:49:55 [initandlisten] recover : no journal files present, no recovery needed
Wed Mar 9 19:49:55 [initandlisten] waiting for connections on port 27017
Wed Mar 9 19:49:55 [websvr] web admin interface listening on port 28017
^C
$

Mathias figured out it was signal 12.