> db.test.group({key: {}, condition: {}, initial: {}, reduce: "5 ++ 5"})
2015-02-09T16:35:10.995-0800 I NETWORK  DBClientCursor::init call() failed
2015-02-09T16:35:10.998-0800 E QUERY    Error: error doing query: failed
    at DBQuery._exec (src/mongo/shell/query.js:83:36)
    at DBQuery.hasNext (src/mongo/shell/query.js:240:10)
    at DBCollection.findOne (src/mongo/shell/collection.js:186:19)
    at DB.runCommand (src/mongo/shell/db.js:58:41)
    at DB.groupcmd (src/mongo/shell/db.js:543:20)
    at DBCollection.group (src/mongo/shell/collection.js:1284:21)
    at (shell):1:9 at src/mongo/shell/query.js:83
2015-02-09T16:35:10.999-0800 I NETWORK  trying reconnect to 127.0.0.1:27017 (127.0.0.1) failed
2015-02-09T16:35:10.999-0800 W NETWORK  Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
2015-02-09T16:35:10.999-0800 I NETWORK  reconnect 127.0.0.1:27017 (127.0.0.1) failed failed couldn't connect to server 127.0.0.1:27017 (127.0.0.1), connection attempt failed

2015-02-09T16:35:10.971-0800 D COMMAND  [conn1] run command test.$cmd { group: { key: {}, condition: {}, initial: {}, ns: "test", $reduce: "5 ++ 5" } }
2015-02-09T16:35:10.981-0800 D QUERY    [conn1] V8Scope 0x29b6000 registered for op 16
2015-02-09T16:35:10.981-0800 D QUERY    [conn1] [QLOG] Running query:
ns=test.system.js limit=0 skip=0
Tree: $and
Sort: {}
Proj: {}
2015-02-09T16:35:10.981-0800 D QUERY    [conn1] Running query: query: {} sort: {} projection: {} skip: 0 limit: 0
2015-02-09T16:35:10.981-0800 D QUERY    [conn1] Collection test.system.js does not exist. Using EOF plan: query: {} sort: {} projection: {} skip: 0 limit: 0
2015-02-09T16:35:10.981-0800 D QUERY    [conn1] [QLOG] Not caching executor but returning 0 results.
2015-02-09T16:35:10.981-0800 I QUERY    [conn1] query test.system.js planSummary: EOF ntoreturn:0 ntoskip:0 nscanned:0 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 0ms
2015-02-09T16:35:10.983-0800 E QUERY    [conn1] SyntaxError: Unexpected number at $group reduce setup
2015-02-09T16:35:10.983-0800 D -        [conn1] User Assertion: 16722:SyntaxError: Unexpected number at $group reduce setup
2015-02-09T16:35:10.983-0800 D QUERY    [conn1] V8Scope 0x29b6000 unregistered for op 16
2015-02-09T16:35:10.983-0800 F -        [conn1] Invalid access at address: 0
2015-02-09T16:35:10.991-0800 F -        [conn1] Got signal: 11 (Segmentation fault).

 0x1134d4e 0x11344f2 0x11348e6 0x7f3a107e5180 0x1252636 0x10a410c 0x10a458d 0x10990b7 0x1099129 0x1093cf4 0x10941e9 0xac3a0c 0xcfb32a 0x96576e 0x9ccc6d 0xa6f29a 0xa704be 0xa7134c 0xcbed85 0xb92994 0x7f9030 0x10effe3 0x7f3a107dc2d4 0x7f3a0f8efc0d
----- BEGIN BACKTRACE -----
{"backtrace":[{"b":"400000","o":"D34D4E"},{"b":"400000","o":"D344F2"},{"b":"400000","o":"D348E6"},{"b":"7F3A107D5000","o":"10180"},{"b":"400000","o":"E52636"},{"b":"400000","o":"CA410C"},{"b":"400000","o":"CA458D"},{"b":"400000","o":"C990B7"},{"b":"400000","o":"C99129"},{"b":"400000","o":"C93CF4"},{"b":"400000","o":"C941E9"},{"b":"400000","o":"6C3A0C"},{"b":"400000","o":"8FB32A"},{"b":"400000","o":"56576E"},{"b":"400000","o":"5CCC6D"},{"b":"400000","o":"66F29A"},{"b":"400000","o":"6704BE"},{"b":"400000","o":"67134C"},{"b":"400000","o":"8BED85"},{"b":"400000","o":"792994"},{"b":"400000","o":"3F9030"},{"b":"400000","o":"CEFFE3"},{"b":"7F3A107D5000","o":"72D4"},{"b":"7F3A0F807000","o":"E8C0D"}],"processInfo":{ "mongodbVersion" : "3.0.0-rc9-pre-", "gitVersion" : "425e072cc40c4389d1761f43f2900c117c96909c", "uname" : { "sysname" : "Linux", "release" : "3.19.0-gentoo", "version" : "#1 SMP PREEMPT Mon Feb 9 09:28:22 PST 2015", "machine" : "x86_64" }, "somap" : [ { "elfType" : 2, "b" : "400000" }, { "b" : "7FFF6B0CC000", "path" : "linux-vdso.so.1", "elfType" : 3, "buildId" : "31327C2EC653AA31647B1433CA6DCF85E7EAF554" }, { "b" : "7F3A107D5000", "path" : "/lib64/libpthread.so.0", "elfType" : 3 }, { "b" : "7F3A105CD000", "path" : "/lib64/librt.so.1", "elfType" : 3 }, { "b" : "7F3A103C9000", "path" : "/lib64/libdl.so.2", "elfType" : 3 }, { "b" : "7F3A100B9000", "path" : "/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/libstdc++.so.6", "elfType" : 3 }, { "b" : "7F3A0FDBE000", "path" : "/lib64/libm.so.6", "elfType" : 3 }, { "b" : "7F3A0FBA7000", "path" : "/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/libgcc_s.so.1", "elfType" : 3 }, { "b" : "7F3A0F807000", "path" : "/lib64/libc.so.6", "elfType" : 3 }, { "b" : "7F3A109F0000", "path" : "/lib64/ld-linux-x86-64.so.2", "elfType" : 3 } ] }}
 mongod(_ZN5mongo15printStackTraceERSo+0x3E) [0x1134d4e]
 mongod(+0xD344F2) [0x11344f2]
 mongod(+0xD348E6) [0x11348e6]
 libpthread.so.0(+0x10180) [0x7f3a107e5180]
 mongod(_ZN2v82V837AdjustAmountOfExternalAllocatedMemoryEl+0x16) [0x1252636]
 mongod(_ZN5boost6detail17sp_counted_impl_pIN5mongo10BSONHolderEE7disposeEv+0x2C) [0x10a410c]
 mongod(_ZN5mongo10ObjTrackerINS_10BSONHolderEED1Ev+0x8D) [0x10a458d]
 mongod(_ZN5mongo7V8ScopeD1Ev+0x207) [0x10990b7]
 mongod(_ZN5mongo7V8ScopeD0Ev+0x9) [0x1099129]
 mongod(_ZN5mongo11PooledScopeD1Ev+0x954) [0x1093cf4]
 mongod(_ZN5mongo11PooledScopeD0Ev+0x9) [0x10941e9]
 mongod(_ZN5mongo10GroupStageD0Ev+0x6C) [0xac3a0c]
 mongod(_ZN5mongo12PlanExecutorD1Ev+0x6A) [0xcfb32a]
 mongod(_ZN5boost14checked_deleteIN5mongo12PlanExecutorEEEvPT_+0xE) [0x96576e]
 mongod(_ZN5mongo12GroupCommand3runEPNS_16OperationContextERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0xC3D) [0x9ccc6d]
 mongod(_ZN5mongo12_execCommandEPNS_16OperationContextEPNS_7CommandERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0x3A) [0xa6f29a]
 mongod(_ZN5mongo7Command11execCommandEPNS_16OperationContextEPS0_iPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0xF8E) [0xa704be]
 mongod(_ZN5mongo12_runCommandsEPNS_16OperationContextEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x62C) [0xa7134c]
 mongod(_ZN5mongo8runQueryEPNS_16OperationContextERNS_7MessageERNS_12QueryMessageERKNS_15NamespaceStringERNS_5CurOpES3_b+0x21C5) [0xcbed85]
 mongod(_ZN5mongo16assembleResponseEPNS_16OperationContextERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortEb+0xA34) [0xb92994]
 mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0xF0) [0x7f9030]
 mongod(_ZN5mongo17PortMessageServer17handleIncomingMsgEPv+0x2F3) [0x10effe3]
 libpthread.so.0(+0x72D4) [0x7f3a107dc2d4]
 libc.so.6(clone+0x6D) [0x7f3a0f8efc0d]
-----  END BACKTRACE  -----

$ ./mongod --version
db version v3.0.0-rc9-pre-
git version: 425e072cc40c4389d1761f43f2900c117c96909c