{ "mode": "man", "parameter": "jdb", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/jdb/1/json", "generated": "2026-09-01T19:03:04Z", "synopsis": "jdb [options] [classname] [arguments]\noptions\nCommand-line options. See Options.\nclassname\nName of the main class to debug.\narguments\nArguments passed to the main() method of the class.", "sections": { "NAME": { "content": "jdb - Finds and fixes bugs in Java platform programs.\n", "subsections": [] }, "SYNOPSIS": { "content": "jdb [options] [classname] [arguments]\n\n\noptions\nCommand-line options. See Options.\n\nclassname\nName of the main class to debug.\n\narguments\nArguments passed to the main() method of the class.\n", "subsections": [] }, "DESCRIPTION": { "content": "The Java Debugger (JDB) is a simple command-line debugger for Java classes. The jdb command\nand its options call the JDB. The jdb command demonstrates the Java Platform Debugger\nArchitecture (JDBA) and provides inspection and debugging of a local or remote Java Virtual\nMachine (JVM). See Java Platform Debugger Architecture (JDBA) at\nhttp://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html\n\nSTART A JDB SESSION\nThere are many ways to start a JDB session. The most frequently used way is to have JDB\nlaunch a new JVM with the main class of the application to be debugged. Do this by\nsubstituting the jdb command for the java command in the command line. For example, if your\napplication's main class is MyClass, then use the following command to debug it under JDB:\n", "subsections": [ { "name": "jdb MyClass", "content": "When started this way, the jdb command calls a second JVM with the specified parameters,\nloads the specified class, and stops the JVM before executing that class's first instruction.\n\nAnother way to use the jdb command is by attaching it to a JVM that is already running.\nSyntax for starting a JVM to which the jdb command attaches when the JVM is running is as\nfollows. This loads in-process debugging libraries and specifies the kind of connection to be\nmade.\n" }, { "name": "java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n MyClass", "content": "You can then attach the jdb command to the JVM with the following command:\n" }, { "name": "jdb -attach 8000", "content": "The MyClass argument is not specified in the jdb command line in this case because the jdb\ncommand is connecting to an existing JVM instead of launching a new JVM.\n\nThere are many other ways to connect the debugger to a JVM, and all of them are supported by\nthe jdb command. The Java Platform Debugger Architecture has additional documentation on\nthese connection options.\n\nBASIC JDB COMMANDS\nThe following is a list of the basic jdb commands. The JDB supports other commands that you\ncan list with the -help option.\n\nhelp or ?\nThe help or ? commands display the list of recognized commands with a brief\ndescription.\n\nrun After you start JDB and set breakpoints, you can use the run command to execute the\ndebugged application. The run command is available only when the jdb command starts\nthe debugged application as opposed to attaching to an existing JVM.\n\ncont Continues execution of the debugged application after a breakpoint, exception, or\nstep.\n\nprint Displays Java objects and primitive values. For variables or fields of primitive\ntypes, the actual value is printed. For objects, a short description is printed. See\nthe dump command to find out how to get more information about an object.\n\nNote: To display local variables, the containing class must have been compiled with\nthe javac -g option.\n\nThe print command supports many simple Java expressions including those with method\ninvocations, for example:\n\nprint MyClass.myStaticField\nprint myObj.myInstanceField\nprint i + j + k (i, j, k are primities and either fields or local variables)\nprint myObj.myMethod() (if myMethod returns a non-null)\nprint new java.lang.String(\"Hello\").length()\n\n\n\ndump For primitive values, the dump command is identical to the print command. For objects,\nthe dump command prints the current value of each field defined in the object. Static\nand instance fields are included. The dump command supports the same set of\nexpressions as the print command.\n\nthreads\nList the threads that are currently running. For each thread, its name and current\nstatus are printed and an index that can be used in other commands. In this example,\nthe thread index is 4, the thread is an instance of java.lang.Thread, the thread name\nis main, and it is currently running.\n\n4. (java.lang.Thread)0x1 main running\n\n\n\nthread Select a thread to be the current thread. Many jdb commands are based on the setting\nof the current thread. The thread is specified with the thread index described in the\nthreads command.\n\nwhere The where command with no arguments dumps the stack of the current thread. The\nwhereall command dumps the stack of all threads in the current thread group. The\nwherethreadindex command dumps the stack of the specified thread.\n\nIf the current thread is suspended either through an event such as a breakpoint or\nthrough the suspend command, then local variables and fields can be displayed with the\nprint and dump commands. The up and down commands select which stack frame is the\ncurrent stack frame.\n\nBREAKPOINTS\nBreakpoints can be set in JDB at line numbers or at the first instruction of a method, for\nexample:\n\n• The command stop at MyClass:22 sets a breakpoint at the first instruction for line 22 of\nthe source file containing MyClass.\n\n• The command stop in java.lang.String.length sets a breakpoint at the beginning of the\nmethod java.lang.String.length.\n\n• The command stop in MyClass. uses to identify the static initialization\ncode for MyClass.\n\nWhen a method is overloaded, you must also specify its argument types so that the proper\nmethod can be selected for a breakpoint. For example, MyClass.myMethod(int,java.lang.String)\nor MyClass.myMethod().\n\nThe clear command removes breakpoints using the following syntax: clear MyClass:45. Using the\nclear or stop command with no argument displays a list of all breakpoints currently set. The\ncont command continues execution.\n\nSTEPPING\nThe step command advances execution to the next line whether it is in the current stack frame\nor a called method. The next command advances execution to the next line in the current stack\nframe.\n\nEXCEPTIONS\nWhen an exception occurs for which there is not a catch statement anywhere in the throwing\nthread's call stack, the JVM typically prints an exception trace and exits. When running\nunder JDB, however, control returns to JDB at the offending throw. You can then use the jdb\ncommand to diagnose the cause of the exception.\n\nUse the catch command to cause the debugged application to stop at other thrown exceptions,\nfor example: catch java.io.FileNotFoundException or catchmypackage.BigTroubleException. Any\nexception that is an instance of the specified class or subclass stops the application at the\npoint where it is thrown.\n\nThe ignore command negates the effect of an earlier catch command. The ignore command does\nnot cause the debugged JVM to ignore specific exceptions, but only to ignore the debugger.\n" } ] }, "OPTIONS": { "content": "When you use the jdb command instead of the java command on the command line, the jdb command\naccepts many of the same options as the java command, including -D, -classpath, and -X\noptions. The following list contains additional options that are accepted by the jdb command.\n\nOther options are supported to provide alternate mechanisms for connecting the debugger to\nthe JVM it is to debug. For additional documentation about these connection alternatives, see\nJava Platform Debugger Architecture (JPDA) at\nhttp://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html\n", "subsections": [ { "name": "-help", "content": "Displays a help message.\n\n-sourcepath dir1:dir2: . . .\nUses the specified path to search for source files in the specified path. If this\noption is not specified, then use the default path of dot (.).\n\n-attach address\nAttaches the debugger to a running JVM with the default connection mechanism.\n\n-listen address\nWaits for a running JVM to connect to the specified address with a standard connector.\n" }, { "name": "-launch", "content": "Starts the debugged application immediately upon startup of JDB. The -launch option\nremoves the need for the run command. The debugged application is launched and then\nstopped just before the initial application class is loaded. At that point, you can\nset any necessary breakpoints and use the cont command to continue execution.\n" }, { "name": "-listconnectors", "content": "List the connectors available in this JVM.\n\n-connect connector-name:name1=value1\nConnects to the target JVM with the named connector and listed argument values.\n" }, { "name": "-dbgtrace [_flags_]", "content": "Prints information for debugging the jdb command.\n" }, { "name": "-tclient", "content": "Runs the application in the Java HotSpot VM client.\n" }, { "name": "-tserver", "content": "Runs the application in the Java HotSpot VM server.\n" }, { "name": "-J_option_", "content": "Passes option to the JVM, where option is one of the options described on the\nreference page for the Java application launcher. For example, -J-Xms48m sets the\nstartup memory to 48 MB. See java(1).\n" } ] }, "OPTIONS FORWARDED TO THE DEBUGGER PROCESS": { "content": "-v -verbose[:class|gc|jni]\nTurns on verbose mode.\n\n-Dname=value\nSets a system property.\n\n-classpath dir\nLists directories separated by colons in which to look for classes.\n", "subsections": [ { "name": "-X_option_", "content": "Nonstandard target JVM option.\n" } ] }, "SEE ALSO": { "content": "• javac(1)\n\n• java(1)\n\n• javah(1)\n\n• javap(1)\n\nJDK 8 21 November 2013 jdb(1)", "subsections": [] } }, "summary": "jdb - Finds and fixes bugs in Java platform programs.", "flags": [ { "flag": "", "long": null, "arg": null, "description": "Displays a help message. -sourcepath dir1:dir2: . . . Uses the specified path to search for source files in the specified path. If this option is not specified, then use the default path of dot (.). -attach address Attaches the debugger to a running JVM with the default connection mechanism. -listen address Waits for a running JVM to connect to the specified address with a standard connector." }, { "flag": "", "long": null, "arg": null, "description": "Starts the debugged application immediately upon startup of JDB. The -launch option removes the need for the run command. The debugged application is launched and then stopped just before the initial application class is loaded. At that point, you can set any necessary breakpoints and use the cont command to continue execution." }, { "flag": "", "long": null, "arg": null, "description": "List the connectors available in this JVM. -connect connector-name:name1=value1 Connects to the target JVM with the named connector and listed argument values." }, { "flag": "", "long": null, "arg": null, "description": "Prints information for debugging the jdb command." }, { "flag": "", "long": null, "arg": null, "description": "Runs the application in the Java HotSpot VM client." }, { "flag": "", "long": null, "arg": null, "description": "Runs the application in the Java HotSpot VM server." }, { "flag": "", "long": null, "arg": null, "description": "Passes option to the JVM, where option is one of the options described on the reference page for the Java application launcher. For example, -J-Xms48m sets the startup memory to 48 MB. See java(1)." } ], "examples": [], "see_also": [ { "name": "javac", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/javac/1/json" }, { "name": "java", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/java/1/json" }, { "name": "javah", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/javah/1/json" }, { "name": "javap", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/javap/1/json" } ] }