jmap UnknownHostException什么意思

在linux环境下执行jmap -histo pid 报错

Attaching to remote server pid, please wait...
Error attaching to remote server: java.rmi.UnknownHostException: Unknown host: pid; nested exception is:
java.net.UnknownHostException: pid
sun.jvm.hotspot.debugger.DebuggerException: java.rmi.UnknownHostException: Unknown host: pid; nested exception is:
java.net.UnknownHostException: pid
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.ObjectHistogram.main(ObjectHistogram.java:64)
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.jmap.JMap.runTool(JMap.java:201)
at sun.tools.jmap.JMap.main(JMap.java:130)
Caused by: java.rmi.UnknownHostException: Unknown host: pid; nested exception is:
java.net.UnknownHostException: pid
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:616)
at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216)
at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202)
at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:342)
at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
at java.rmi.Naming.lookup(Naming.java:101)
at sun.jvm.hotspot.RMIHelper.lookup(RMIHelper.java:113)
... 13 more
Caused by: java.net.UnknownHostException: pid
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:211)
at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:40)
at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:148)
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:613)
... 19 more
求高手解答，这是什么意思。
用jstack命令没有问题，但是只能看进程。现在想看内存消耗情况，提示这个错误。