Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff7fcc700 (LWP 23947)]
0x00007ffff75675c8 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(gdb) f 2
#2  0x00000000012a1197 in mongo::(anonymous namespace)::cloneCollectionAsCapped (txn=0x7ffff7fcb7c0, db=0x0, shortFrom=..., shortTo=..., size=4096, temp=false, logForReplication=true)
    at src/mongo/db/commands/collection_to_capped.cpp:60
60	        string fromNs = db->name() + "." + shortFrom;
(gdb) p db
$1 = (mongo::Database *) 0x0
(gdb) bt
#0  0x00007ffff75675c8 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1  0x000000000114067c in std::operator+<char, std::char_traits<char>, std::allocator<char> > (__lhs=..., __rhs=0x1f83032 ".") at /usr/include/c++/4.8/bits/basic_string.h:2405
#2  0x00000000012a1197 in mongo::(anonymous namespace)::cloneCollectionAsCapped (txn=0x7ffff7fcb7c0, db=0x0, shortFrom=..., shortTo=..., size=4096, temp=false, logForReplication=true)
    at src/mongo/db/commands/collection_to_capped.cpp:60
#3  0x00000000012a2227 in mongo::CmdCloneCollectionAsCapped::run (this=0x2863ce0 <mongo::cmdCloneCollectionAsCapped>, txn=0x7ffff7fcb7c0, dbname=..., jsobj=..., errmsg=..., result=..., fromRepl=false)
    at src/mongo/db/commands/collection_to_capped.cpp:179
#4  0x0000000001332b65 in mongo::_execCommand (txn=0x7ffff7fcb7c0, c=0x2863ce0 <mongo::cmdCloneCollectionAsCapped>, dbname=..., cmdObj=..., queryOptions=0, errmsg=..., result=..., fromRepl=false)
    at src/mongo/db/dbcommands.cpp:1267
#5  0x0000000001333ae2 in mongo::Command::execCommand (txn=0x7ffff7fcb7c0, c=0x2863ce0 <mongo::cmdCloneCollectionAsCapped>, queryOptions=0, cmdns=0x33ec414 "test.$cmd", cmdObj=..., result=..., 
    fromRepl=false) at src/mongo/db/dbcommands.cpp:1483
#6  0x00000000013343c4 in mongo::_runCommands (txn=0x7ffff7fcb7c0, ns=0x33ec414 "test.$cmd", _cmdobj=..., b=..., anObjBuilder=..., fromRepl=false, queryOptions=0) at src/mongo/db/dbcommands.cpp:1558
#7  0x0000000001535e8c in mongo::runCommands (txn=0x7ffff7fcb7c0, ns=0x33ec414 "test.$cmd", jsobj=..., curop=..., b=..., anObjBuilder=..., fromRepl=false, queryOptions=0) at src/mongo/db/query/find.cpp:137
#8  0x0000000001537eb4 in mongo::runQuery (txn=0x7ffff7fcb7c0, m=..., q=..., nss=..., curop=..., result=..., fromDBDirectClient=false) at src/mongo/db/query/find.cpp:606
#9  0x000000000143e04c in mongo::receivedQuery (txn=0x7ffff7fcb7c0, c=..., dbresponse=..., m=..., fromDBDirectClient=false) at src/mongo/db/instance.cpp:220
#10 0x000000000143f1f6 in mongo::assembleResponse (txn=0x7ffff7fcb7c0, m=..., dbresponse=..., remote=..., fromDBDirectClient=false) at src/mongo/db/instance.cpp:403
#11 0x000000000113f218 in mongo::MyMessageHandler::process (this=0x30b21c8, m=..., port=0x30d9570, le=0x354c2d0) at src/mongo/db/db.cpp:206
#12 0x00000000018df52a in mongo::PortMessageServer::handleIncomingMsg (arg=0x30d9570) at src/mongo/util/net/message_server_port.cpp:230
#13 0x00007ffff7bc4182 in start_thread (arg=0x7ffff7fcc700) at pthread_create.c:312
#14 0x00007ffff6cc500d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111