JPS(1)

💅 JPS(1) — bestie, this is the jps page

okay so before anything else: this is jps, a page from the JDK Commands manual, and it's here to help you list the instrumented JVMs on the target system. that's the whole vibe. let's get into it 🫶

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✨ SYNOPSIS ✨

heads up bestie: this command is experimental and unsupported. it's giving "we let you have it but don't come crying to us" 😭

jps [-q] [-mlvV] [hostid]

jps [-help]

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🎀 OPTIONS 🎀

• -q — suppresses the output of the class name, JAR file name, and arguments passed to the main method, producing a list of only local JVM identifiers. quiet luxury, literally 💅
• -mlvV — you can specify any combination of these options. mix and match, it's a build-your-own-adventure:
  • -m displays the arguments passed to the main method. The output may be null for embedded JVMs. (so like… don't panic if it's empty, it's a whole thing 🫠)
  • -l displays the full package name for the application's main class or the full path name to the application's JAR file. long form, no shortcuts, main character energy 👑
  • -v displays the arguments passed to the JVM.
  • -V suppresses the output of the class name, JAR file name, and arguments passed to the main method, producing a list of only local JVM identifiers.
• hostid — the identifier of the host for which the process report should be generated. The hostid can include optional components that indicate the communications protocol, port number, and other implementation specific data. See Host Identifier below, bestie, it's got its own section 🌸
• -help — displays the help message for the jps command. when in doubt, ask for help, no shame in it 💖

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🦋 DESCRIPTION 🦋

The jps command lists the instrumented Java HotSpot VMs on the target system. And here's the catch: the command is limited to reporting information on JVMs for which it has the access permissions. permissions check first, always 🔒

If the jps command is run without specifying a hostid, then it searches for instrumented JVMs on the local host. If started with a hostid, then it searches for JVMs on the indicated host, using the specified protocol and port. A jstatd process is assumed to be running on the target host. (assumed!! so like, have it running pls 🙏)

The jps command reports the local JVM identifier, or lvmid, for each instrumented JVM found on the target system. The lvmid is typically, but not necessarily, the operating system's process identifier for the JVM process. With no options, the jps command lists each Java application's lvmid followed by the short form of the application's class name or jar file name. The short form of the class name or JAR file name omits the class's package information or the JAR files path information. short form = the ✨condensed✨ version, iykyk

The jps command uses the Java launcher to find the class name and arguments passed to the main method. If the target JVM is started with a custom launcher, then the class or JAR file name, and the arguments to the main method aren't available. In this case, the jps command outputs the string Unknown for the class name, or JAR file name, and for the arguments to the main method. and honestly? Unknown is doing its best 😭

The list of JVMs produced by the jps command can be limited by the permissions granted to the principal running the command. The command lists only the JVMs for which the principal has access rights as determined by operating system-specific access control mechanisms. gatekeeping, but make it OS-level 💀

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🧚 HOST IDENTIFIER 🧚

The host identifier, or hostid, is a string that indicates the target system. The syntax of the hostid string corresponds to the syntax of a URI:

[protocol:][[//]hostname][:port][/servername]

• protocol — the communications protocol. If the protocol is omitted and a hostname isn't specified, then the default protocol is a platform-specific, optimized, local protocol. If the protocol is omitted and a host name is specified, then the default protocol is rmi. defaults doing their thing ✨
• hostname — a host name or IP address that indicates the target host. If you omit the hostname parameter, then the target host is the local host. staying local, love that for you 🏠
• port — the default port for communicating with the remote server. If the hostname parameter is omitted or the protocol parameter specifies an optimized, local protocol, then the port parameter is ignored. Otherwise, treatment of the port parameter is implementation-specific. For the default rmi protocol, the port parameter indicates the port number for the rmiregistry on the remote host. If the port parameter is omitted, and the protocol parameter indicates rmi, then the default rmiregistry port (1099) is used. write that down: 1099 🎀
• servername — the treatment of this parameter depends on the implementation. For the optimized, local protocol, this field is ignored. For the rmi protocol, this parameter is a string that represents the name of the RMI remote object on the remote host. See the jstatd command -n option. go check that one out too 🫶

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🌈 OUTPUT FORMAT OF THE JPS COMMAND 🌈

The output of the jps command has the following pattern:

lvmid [ [ classname | JARfilename | "Unknown"] [ arg* ] [ jvmarg* ] ]

All output tokens are separated by white space. An arg value that includes embedded white space introduces ambiguity when attempting to map arguments to their actual positional parameters. yes this is chaotic, no we can't fix it, it's the format's fault 😭

Note: it's recommended that you don't write scripts to parse jps output because the format might change in future releases. If you write scripts that parse jps output, then expect to modify them for future releases of this tool. fr fr, don't do it, future-you will not be thanking present-you 💀

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⭐ EXAMPLES ⭐

This section provides examples of the jps command.

List the instrumented JVMs on the local host:

jps
18027 Java2Demo.JAR
18032 jps
18005 jstat

The following example lists the instrumented JVMs on a remote host. This example assumes that the jstat server and either the its internal RMI registry or a separate external rmiregistry process are running on the remote host on the default port (port 1099). It also assumes that the local host has appropriate permissions to access the remote host. This example includes the -l option to output the long form of the class names or JAR file names.

jps -l remote.domain
3002 /opt/jdk1.7.0/demo/jfc/Java2D/Java2Demo.JAR
2857 sun.tools.jstatd.jstatd

The following example lists the instrumented JVMs on a remote host with a nondefault port for the RMI registry. This example assumes that the jstatd server, with an internal RMI registry bound to port 2002, is running on the remote host. This example also uses the -m option to include the arguments passed to the main method of each of the listed Java applications.

jps -m remote.domain:2002
3002 /opt/jdk1.7.0/demo/jfc/Java2D/Java2Demo.JAR
3102 sun.tools.jstatd.jstatd -p 2002

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and that's the page, bestie!! 🎉 this little ditty comes to you from JDK 21, dated 2023, filed under JPS(1) — go forth and list those JVMs, you absolute icon 💖🌸🦋