A single general command-line option \f3-help\fR or \f3-options\fR\&. See General Options\&.
.TP
\fIoutputOptions\fR
One or more output options that consist of a single \f3statOption\fR, plus any of the \f3-t\fR, \f3-h\fR, and \f3-J\fR options\&. See Output Options\&.
.TP
\fIvmid\fR
Virtual machine identifier, which is a string that indicates the target JVM\&. The general syntax is the following:
The syntax of the \f3vmid\fR string corresponds to the syntax of a URI\&. The \f3vmid\fR string can vary from a simple integer that represents a local JVM to a more complex construction that specifies a communications protocol, port number, and other implementation-specific values\&. See Virtual Machine Identifier\&.
.TP
\fIinterval\fR [s|ms]
Sampling interval in the specified units, seconds (s) or milliseconds (ms)\&. Default units are milliseconds\&. Must be a positive integer\&. When specified, the \f3jstat\fR command produces its output at each interval\&.
.TP
\fIcount\fR
Number of samples to display\&. The default value is infinity which causes the \f3jstat\fR command to display statistics until the target JVM terminates or the \f3jstat\fR command is terminated\&. This value must be a positive integer\&.
.SHDESCRIPTION
The \f3jstat\fR command displays performance statistics for an instrumented Java HotSpot VM\&. The target JVM is identified by its virtual machine identifier, or \f3vmid\fR option\&.
.SHVIRTUAL\MACHINE\IDENTIFIER
The syntax of the \f3vmid\fR string corresponds to the syntax of a URI:
The communications protocol\&. If the \fIprotocol\fR value is omitted and a host name is not specified, then the default protocol is a platform-specific optimized local protocol\&. If the \fIprotocol\fR value is omitted and a host name is specified, then the default protocol is \f3rmi\fR\&.
.TP
\fIlvmid\fR
The local virtual machine identifier for the target JVM\&. The \f3lvmid\fR is a platform-specific value that uniquely identifies a JVM on a system\&. The \f3lvmid\fR is the only required component of a virtual machine identifier\&. The \f3lvmid\fR is typically, but not necessarily, the operating system\&'s process identifier for the target JVM process\&. You can use the \f3jps\fR command to determine the \f3lvmid\fR\&. Also, you can determine the \f3lvmid\fR on UNIX platforms with the \f3ps\fR command, and on Windows with the Windows Task Manager\&.
.TP
\fIhostname\fR
A hostname or IP address that indicates the target host\&. If the \fIhostname\fR value is omitted, then the target host is the local host\&.
.TP
\fIport\fR
The default port for communicating with the remote server\&. If the \fIhostname\fR value is omitted or the \fIprotocol\fR value specifies an optimized, local protocol, then the \fIport\fR value is ignored\&. Otherwise, treatment of the \f3port\fR parameter is implementation-specific\&. For the default \f3rmi\fR protocol, the port value indicates the port number for the rmiregistry on the remote host\&. If the \fIport\fR value is omitted and the \fIprotocol\fR value indicates \f3rmi\fR, then the default rmiregistry port (1099) is used\&.
.TP
\fIservername\fR
The treatment of the \f3servername\fR parameter depends on implementation\&. For the optimized local protocol, this field is ignored\&. For the \f3rmi\fR protocol, it represents the name of the RMI remote object on the remote host\&.
.SHOPTIONS
The \f3jstat\fR command supports two types of options, general options and output options\&. General options cause the \f3jstat\fR command to display simple usage and version information\&. Output options determine the content and format of the statistical output\&.
.PP
All options and their functionality are subject to change or removal in future releases\&.
.SSGENERAL\OPTIONS
If you specify one of the general options, then you cannot specify any other option or parameter\&.
.TP
-help
.br
Displays a help message\&.
.TP
-options
.br
Displays a list of static options\&. See Output Options\&.
.SSOUTPUT\OPTIONS
If you do not specify a general option, then you can specify output options\&. Output options determine the content and format of the \f3jstat\fR command\&'s output, and consist of a single \f3statOption\fR, plus any of the other output options (\f3-h\fR, \f3-t\fR, and \f3-J\fR)\&. The \f3statOption\fR must come first\&.
.PP
Output is formatted as a table, with columns that are separated by spaces\&. A header row with titles describes the columns\&. Use the \f3-h\fR option to set the frequency at which the header is displayed\&. Column header names are consistent among the different options\&. In general, if two options provide a column with the same name, then the data source for the two columns is the same\&.
.PP
Use the \f3-t\fR 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 the target JVM started\&. 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\&.
.PP
Use the interval and count parameters to determine how frequently and how many times, respectively, the \f3jstat\fR command displays its output\&.
.PP
\fINote:\fR Do not to write scripts to parse the \f3jstat\fR command\&'s output because the format might change in future releases\&. If you write scripts that parse \f3jstat\fR command output, then expect to modify them for future releases of this tool\&.
.TP
-\fIstatOption\fR
.br
Determines the statistics information the \f3jstat\fR command displays\&. The following lists the available options\&. Use the \f3-options\fR general option to display the list of options for a particular platform installation\&. See Stat Options and Output\&.
\f3gccause\fR: Displays a summary about garbage collection statistics (same as \f3-gcutil\fR), with the cause of the last and current (when applicable) garbage collection events\&.
Displays a column header every \fIn\fR samples (output rows), where \fIn\fR is a positive integer\&. Default value is 0, which displays the column header the first row of data\&.
Passes \f3javaOption\fR to the Java application launcher\&. For example, \f3-J-Xms48m\fR sets the startup memory to 48 MB\&. For a complete list of options, see java(1)\&.
.SSSTAT\OPTIONS\AND\OUTPUT
The following information summarizes the columns that the \f3jstat\fR command outputs for each \fIstatOption\fR\&.
This option displays the same summary of garbage collection statistics as the \f3-gcutil\fR option, but includes the causes of the last garbage collection event and (when applicable) the current garbage collection event\&. In addition to the columns listed for \f3-gcutil\fR, this option adds the following columns\&.
Garbage collection statistics, including garbage collection Events\&.
\f3E\fR: Eden space utilization as a percentage of the space\&'s current capacity\&.
\f3O\fR: Old space utilization as a percentage of the space\&'s current capacity\&.
\f3M\fR: Metaspace utilization as a percentage of the space\&'s current capacity\&.
\f3YGC\fR: Number of young generation GC events\&.
\f3YGCT\fR: Young generation garbage collection time\&.
\f3FGC\fR: Number of full GC events\&.
\f3FGCT\fR: Full garbage collection time\&.
\f3GCT\fR: Total garbage collection time\&.
.TP
-printcompilation \fIoption\fR
.br
Java HotSpot VM compiler method statistics\&.
\f3Compiled\fR: Number of compilation tasks performed by the most recently compiled method\&.
\f3Size\fR: Number of bytes of byte code of the most recently compiled method\&.
\f3Type\fR: Compilation type of the most recently compiled method\&.
\f3Method\fR: Class name and method name identifying the most recently compiled method\&. Class name uses slash (/) instead of dot (\&.) as a name space separator\&. Method name is the method within the specified class\&. The format for these two fields is consistent with the HotSpot \f3-XX:+PrintComplation\fR option\&.
.SHEXAMPLES
This section presents some examples of monitoring a local JVM with an \fIlvmid\fR of 21891\&.
.SSTHE\GCUTIL\OPTION
This example attaches to lvmid 21891 and takes 7 samples at 250 millisecond intervals and displays the output as specified by the -\f3gcutil\fR option\&.
.PP
The output of this example shows that a young generation collection occurred between the third and fourth sample\&. The collection took 0\&.001 seconds and promoted objects from the eden space (E) to the old space (O), resulting in an increase of old space utilization from 9\&.49% to 9\&.51%\&. Before the collection, the survivor space was 12\&.44% utilized, but after this collection it is only 7\&.74% utilized\&.
This example attaches to lvmid 21891 and takes samples at 250 millisecond intervals and displays the output as specified by \f3-gcutil\fR option\&. In addition, it uses the \f3-h3\fR option to output the column header after every 3 lines of data\&.
.PP
In addition to showing the repeating header string, this example shows that between the second and third samples, a young GC occurred\&. Its duration was 0\&.001 seconds\&. The collection found enough active data that the survivor space 0 utilization (S0U) would have exceeded the desired survivor Size (DSS)\&. As a result, objects were promoted to the old generation (not visible in this output), and the tenuring threshold (TT) was lowered from 31 to 2\&.
.PP
Another collection occurs between the fifth and sixth samples\&. This collection found very few survivors and returned the tenuring threshold to 31\&.
This example attaches to lvmid 21891 and takes 3 samples at 250 millisecond intervals\&. The \f3-t\fR option is used to generate a time stamp for each sample in the first column\&.
.PP
The Timestamp column reports the elapsed time in seconds since the start of the target JVM\&. In addition, the \f3-gcoldcapacity\fR output shows the old generation capacity (OGC) and the old space capacity (OC) increasing as the heap expands to meet allocation or promotion demands\&. The old generation capacity (OGC) has grown to from 11,696 KB to 13820 KB after the eighty-first full garbage collection (FGC)\&. The maximum capacity of the generation (and space) is 60,544 KB (OGCMX), so it still has room to expand\&.
This example attaches to lvmid 40496 on the system named remote\&.domain using the \f3-gcutil\fR option, with samples taken every second indefinitely\&.
.PP
The lvmid is combined with the name of the remote host to construct a \fIvmid\fR of \f340496@remote\&.domain\fR\&. This vmid results in the use of the \f3rmi\fR protocol to communicate to the default \f3jstatd\fR server on the remote host\&. The \f3jstatd\fR server is located using the rmiregistry on \f3remote\&.domain\fR that is bound to the default rmiregistry port (port 1099)\&.