gistfile1.txt

$ jstack -m core.51134 
Attaching to remote server core.51134, please wait...
Error attaching to remote server: java.net.MalformedURLException: invalid authority: //core.51134/SARemoteDebugger
sun.jvm.hotspot.debugger.DebuggerException: java.net.MalformedURLException: invalid authority: //core.51134/SARemoteDebugger
        at sun.jvm.hotspot.RMIHelper.lookup(RMIHelper.java:115)
        at sun.jvm.hotspot.HotSpotAgent.connectRemoteDebugger(HotSpotAgent.java:517)
        at sun.jvm.hotspot.HotSpotAgent.setupDebugger(HotSpotAgent.java:374)
        at sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:304)
        at sun.jvm.hotspot.HotSpotAgent.attach(HotSpotAgent.java:183)
        at sun.jvm.hotspot.tools.Tool.start(Tool.java:196)
        at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
        at sun.jvm.hotspot.tools.JStack.main(JStack.java:92)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sun.tools.jstack.JStack.runJStackTool(JStack.java:140)
        at sun.tools.jstack.JStack.main(JStack.java:106)
Caused by: java.net.MalformedURLException: invalid authority: //core.51134/SARemoteDebugger
        at java.rmi.Naming.intParseURL(Naming.java:330)
        at java.rmi.Naming.parseURL(Naming.java:237)
        at java.rmi.Naming.lookup(Naming.java:96)
        at sun.jvm.hotspot.RMIHelper.lookup(RMIHelper.java:113)
        ... 13 more

http://stackoverflow.com/questions/37331266/jstack-throws-exception-interrogating-a-core

こうかしら？
jstack -m /usr/java/jdk1.8.0_92/bin/java core.51134