jstat – Java Virtual Machine Statistics Monitoring Tool
generalOption A single general command-line option (-help or -options) outputOptions One or more output options, consisting of a single statOption. plus any of the -t, -h, and -J options. vmid Virtual machine identifier, a string indicating the target Java virtual machine (JVM). The general syntax is The syntax of the vmid string largely corresponds to the syntax of a URI. The vmid can vary from a simple integer representing a local JVM to a more complex construction specifying a communications protocol, port number, and other implementation-specific values. See Virtual Machine Identifier for details. interval [s|ms] Sampling interval in the specified units, seconds (s) or milliseconds (ms). Default units are milliseconds. Must be a positive integer. If specified, jstat will produce its output at each interval. count Number of samples to display. Default value is infinity; that is, jstat displays statistics until the target JVM terminates or the jstat command is terminated. Must be a positive integer.
The jstat tool displays performance statistics for an instrumented HotSpot Java virtual machine (JVM). The target JVM is identified by its virtual machine identifier, or vmid option described below.
NOTE. This utility is unsupported and may not be available in future versions of the JDK. It is not currently available on Windows 98 and Windows ME. platforms.
VIRTUAL MACHINE IDENTIFIER
The syntax of the vmid string largely corresponds to the syntax of a URI:
protocol The communications protocol. If the protocol is omitted and a hostname is not specified, the default protocol is a platform specific optimized local protocol. If the protocol is omitted and a hostname is specified, then the default protocol is rmi. lvmid The local virtual machine identifier for the target JVM. The lvmid is a platform-specific value that uniquely identifies a JVM on a system. The lvmid is the only required component of a virtual machine identifier. The lvmid is typically, but not necessarily, the operating system’s process identifier for the target JVM process. You can use the jps command to determine the lvmid. Also, you can determine lvmid on Unix platforms with the ps command, and on Windows with the Windows Task Manager. hostname A hostname or IP address indicating the target host. If hostname is omitted, then the target host is the local host. port The default port for communicating with the remote server. If the hostname is omitted or the protocol specifies an optimized, local protocol, then port is ignored. Otherwise, treatment of the port parameter is implementation specific. For the default rmi protocol, the port indicates the port number for the rmiregistry on the remote host. If port is omitted, and protocol indicates rmi. then the default rmiregistry port (1099) is used. servername The treatment of this parameter depends on implementation. For the optimized local protocol, this field is ignored. For the rmi protocol, it represents the name of the RMI remote object on the remote host.
The jstat command supports two types of options, general options and output options. General options cause jstat to display simple usage and version information. Output options determine the content and format of the statistical output.
NOTE. All options, and their functionality are subject to change or removal in future releases.
If you specify one of the general options, you cannot specify any other option or parameter.
-help Display help message. -options Display list of statistics options. See the Output Options section below.
If you do not specify a general option, then you can specify output options. Output options determine the content and format of jstat ‘s output, and consist of a single statOption. plus any of the other output options (-h, -t, and -J). The statOption must come first.
Output is formatted as a table, with columns are separated by spaces. A header row with titles describes the columns. Use the -h option to set the frequency at which the header is displayed. Column header names are generally consistent between the different options. In general, if two options provide a column with the same name, then the data source for the two columns are the same.
Use the -t option to display a time stamp column, labeled Timestamp as the first column of output. The Timestamp column contains the elapsed time, in seconds, since startup of the target JVM. The resolution of the time stamp is dependent on various factors and is subject to variation due to delayed thread scheduling on heavily loaded systems.
Use the interval and count parameters to determine how frequently and how many times, respectively, jstat displays its output.
NOTE. You are advised not to write scripts to parse jstat’s output since the format may change in future releases. If you choose to write scripts that parse jstat output, expect to modify them for future releases of this tool.
–statOption Determines the statistics information that jstat displays. The following table lists the available options. Use the -options general option to display the list of options for a particular platform installation.