$ mongod --logpath /dev/null --fork
$ forked process: 93576
all output going to: /dev/null

$ mongo
MongoDB shell version: 1.6.4
connecting to: test
> db.foo.drop()
true
> db.foo.save({x:1});
> bye
$ killall mongod
$ ps ax | grep mongod
$ mongod --logpath /dev/null --fork
forked process: 93591
all output going to: /dev/null
$ mongo
MongoDB shell version: 1.6.4
connecting to: test
> bye
$ !killall
killall mongod
$ mongod --logpath /dev/null --fork
$ forked process: 93596
all output going to: /dev/null
mongo admin
MongoDB shell version: 1.6.4
connecting to: admin
> db.runCommand({fsync: 1, lock: 1});
{
	"info" : "now locked against writes, use db.$cmd.sys.unlock.findOne() to unlock",
	"ok" : 1
}
> bye
$ mongo test
MongoDB shell version: 1.6.4
connecting to: test
> db.foo.find()
  C-c C-c
do you want to kill the current op on the server? (y/n): y
connecting to: test
$ mongo admin
MongoDB shell version: 1.6.4
connecting to: admin
> db.$cmd.sys.unlock.findOne()
{ "ok" : 1, "info" : "unlock requested" }
> bye
$ mongo test
MongoDB shell version: 1.6.4
connecting to: test
> db.foo.find()
{ "_id" : ObjectId("4d1263f9ef032e333a45a6e7"), "x" : 1 }