dtrace(8)

NAME
dtrace - DTrace dynamic tracing compiler and tracing utility

SYNOPSIS
dtrace [-CeFGHhlqSvVwZ] [-b bufsz] [-c cmd]
[-D name [=value]] [-I path] [-L path] [-o output]
[-s script] [-U name] [-x arg [=val]]
[-X a | c | s | t] [-p pid]
[-P provider [[predicate] action]]
[-m [provider:] module [[predicate] action]]
[-f [[provider:] module:] function [[predicate] action]]
[-n [[[provider:] module:] function:]name [[predicate] action]]
[-i probe-id [[predicate] action]]

DESCRIPTION

DTrace is a comprehensive dynamic tracing framework for the Linux operating system. DTrace provides a powerful infrastructure that permits administrators, developers, and service personnel to concisely answer arbitrary questions about the behavior of the operating system and user programs.

The Oracle Linux DTrace Guide describes how to use DTrace to observe, debug, and tune system behavior. Refer to this book for a detailed description of DTrace features, including the bundled DTrace observability tools, instrumentation providers, and the D programming language.

The dtrace command provides a generic interface to the essential services provided by the DTrace facility, including:

    o   Options that list the set of probes and providers currently published by DTrace

    o   Options that enable probes directly using any of the probe description specifiers (provider, module, function, name)

    o   Options that run the D compiler and compile one or more D program files or programs written directly on the command line

    o   Options that generate anonymous tracing programs

    o   Options that generate program stability reports

    o   Options that modify DTrace tracing and buffering behavior and enable additional D compiler features

You can use dtrace to create D scripts by using it in a #! declaration to create an interpreter file. You can also use dtrace to attempt to compile D programs and determine their properties without actually enabling tracing using the -e option. See OPTIONS. See the Oracle Linux DTrace Guide for detailed examples of how to use the dtrace utility to perform these tasks.

OPTIONS

The arguments accepted by the -P, -m, -f, -n, and -i options can include an optional D language predicate enclosed in slashes // and optional D language action statement list enclosed in braces {}. D program code specified on the command line must be appropriately quoted to avoid interpretation of meta-characters by the shell.

The following options are supported:

-b bufsz
    Set principal trace buffer size (bufsz). The trace buffer size can include any of the size suffixes k, m, g, or t. If the buffer space cannot be allocated, dtrace attempts to reduce the buffer size or exit depending on the setting of the bufresize property.

-c cmd
    Run the specified command cmd and exit upon its completion. If more than one -c option is present on the command line, dtrace exits when all commands have exited, reporting the exit status for each child process as it terminates. The process-ID of the first command is made available to any D programs specified on the command line or using the -s option through the $target macro variable. Refer to the Oracle Linux DTrace Guide for more information on macro variables.

-C  Run the C preprocessor cpp(1) over D programs before compiling them. You can pass options to the C preprocessor using the -D, -U, -I, and -H options. You can select the degree of C standard conformance if you use the -X option. For a description of the set of tokens defined by the D compiler when invoking the C preprocessor, see -X.

-D name [=value]
    Define name when invoking cpp(1) (enabled using the -C option). If you specify the equals sign (=) and additional value, the name is assigned the corresponding value. This option passes the -D option to each cpp invocation.

-e  Exit after compiling any requests, but prior to enabling any probes. You can combine this option with D compiler options. This combination verifies that the programs compile without actually executing them and enabling the corresponding instrumentation.

-f[[provider:]module:]function[[predicate]action]]
    Specify function name to trace or list (-l option). The corresponding argument can include any of the probe description forms provider:module:function, module:function, or function. Unspecified probe description fields are left blank and match any probes regardless of the values in those fields. If no qualifiers other than function are specified in the description, all probes with the corresponding function are matched. The -f argument can be suffixed with an optional D probe clause. You can specify more than one -f option on the command line at a time.

-F  Coalesce trace output by identifying function entry and return. Function entry probe reports are indented and their output is prefixed with ->. Function return probe reports are unindented and their output is prefixed with <-. System call entry probe reports are indented and their output is prefixed with =>. System call return probe reports are unindented and their output is prefixed with <=.

-G  Generate an ELF file containing an embedded DTrace program. The DTrace probes specified in the program are saved inside of a relocatable ELF object which can be linked into another program. If the -o option is present, the ELF file is saved using the pathname specified as the argument for this operand. If the -o option is not present and the DTrace program is contained with a file whose name is filename.d, then the ELF file is saved using the name filename.o. Otherwise the ELF file is saved using the name d.out.

-H  Print the pathnames of included files when invoking cpp(1) (enabled using the -C option). This option passes the -H option to each cpp invocation, causing it to display the list of pathnames, one for each line, to stderr.

-h  Generate a header file containing macros that correspond to probes in the specified provider definitions. This option should be used to generate a header file that is included by other source files for later use with the -G option. If the -o option is present, the header file is saved using the pathname specified as the argument for that option. If the -o option is not present and the DTrace program is contained with a file whose name is filename.d, then the header file is saved using the name filename.h.

-i probe-id[[predicate] action]
    Specify probe identifier (probe-id) to trace or list (-l option). You can specify probe IDs using decimal integers as shown by dtrace -l. The -i argument can be suffixed with an optional D probe clause. You can specify more than one -i option at a time.

-I path
    Add the specified directory path to the search path for #include files when invoking cpp(1) (enabled using the -C option). This option passes the -I option to each cpp invocation. The specified path is inserted into the search path ahead of the default directory list.

-L path
    Add the specified directory path to the search path for DTrace libraries. DTrace libraries are used to contain common definitions that can be used when writing D programs. The specified path is added after the default library search path. If it exists, a subdirectory of path named after the minor version of the running kernel (e.g. 3.8) is searched immediately before path. (But take note: dependency analysis is performed only within each directory, not across directories.)

-l  List probes instead of enabling them. If the -l option is specified, dtrace produces a report of the probes matching the descriptions given using the -P, -m, -f, -n, -i, and -s options. If none of these options are specified, this option lists all probes.

-m [[provider:] module: [[predicate] action]]
    Specify module name to trace or list (-l option). The corresponding argument can include any of the probe description forms provider:module or module. Unspecified probe description fields are left blank and match any probes regardless of the values in those fields. If no qualifiers other than module are specified in the description, all probes with a corresponding module are matched. The -m argument can be suffixed with an optional D probe clause. More than one -m option can be specified on the command line at a time.

-n [[[provider:] module:] function:] name [[predicate] action]
    Specify probe name to trace or list (-l option). The corresponding argument can include any of the probe description forms provider:module:function:name, module:function:name, function:name, or name. Unspecified probe description fields are left blank and match any probes regardless of the values in those fields. If no qualifiers other than name are specified in the description, all probes with a corresponding name are matched. The -n argument can be suffixed with an optional D probe clause. More than one -n option can be specified on the command line at a time.

-o output
    Specify the output file for the -G, -h, and -l options, or for the traced data itself. If the -G option is present and the -s option's argument is of the form filename.d and -o is not present, the default output file is filename.o. Otherwise the default output file is d.out.

-p pid
    Grab the specified process-ID pid, cache its symbol tables, and exit upon its completion. If more than one -p option is present on the command line, dtrace exits when all commands have exited, reporting the exit status for each process as it terminates. The first process-ID is made available to any D programs specified on the command line or using the -s option through the $target macro variable. Refer to the Oracle Linux DTrace Guide for more information on macro variables.

-P provider [[predicate] action]
    Specify provider name to trace or list (-l option). The remaining probe description fields module, function, and name are left blank and match any probes regardless of the values in those fields. The -P argument can be suffixed with an optional D probe clause. You can specify more than one -P option on the command line at a time.

-q  Set quiet mode. dtrace suppresses messages such as the number of probes matched by the specified options and D programs and does not print column headers, the CPU ID, the probe ID, or insert newlines into the output. Only data traced and formatted by D program statements such as trace() and printf() is displayed to stdout.

-s  Compile the specified D program source file. If the -e option is present, the program is compiled but instrumentation is not enabled. If the -l option is present, the program is compiled and the set of probes matched by it is listed, but instrumentation is not enabled. If none of -e, -l, or -G are present, the instrumentation specified by the D program is enabled and tracing begins.

-S  Show D compiler intermediate code. The D compiler produces a report of the intermediate code generated for each D program to stderr.

-U name
    Undefine the specified name when invoking cpp(1) (enabled using the -C option). This option passes the -U option to each cpp invocation.

-v  Set verbose mode. If the -v option is specified, dtrace produces a program stability report showing the minimum interface stability and dependency level for the specified D programs. DTrace stability levels are explained in further detail in the Oracle Linux DTrace Guide.

-V  Report the highest D programming interface version supported by dtrace. The version information is printed to stdout and the dtrace command exits. Refer to the Oracle Linux DTrace Guide for more information about DTrace versioning features. In conjunction with -v, also reports information on the version of the dtrace(1) tool and associated library.

-w  Permit destructive actions in D programs specified using the -s, -P, -m, -f, -n, or -i options. If the -w option is not specified, dtrace does not permit the compilation or enabling of a D program that contains destructive actions.

-x arg [=val]
    Enable or modify a DTrace runtime option or D compiler option. The list of options is found in the Oracle Linux DTrace Guide. Boolean options are enabled by specifying their name. Options with values are set by separating the option name and value with an equals sign (=).

-Z  Permit probe descriptions that match zero probes. If the -Z option is not specified, dtrace reports an error and exits if any probe descriptions specified in D program files (-s option) or on the command line (-P, -m, -f, -n, or -i options) contain descriptions that do not match any known probes.

OPERANDS

You can specify zero or more additional arguments on the dtrace command line to define a set of macro variables ($1, $2, and so forth). The additional arguments can be used in D programs specified using the -s option or on the command line. The use of macro variables is described further in the Oracle Linux DTrace Guide.

EXIT STATUS

The following exit values are returned:

0   Successful completion. For D program requests, an exit status of 0 indicates that programs were successfully compiled, probes were successfully enabled, or anonymous state was successfully retrieved. dtrace returns 0 even if the specified tracing requests encountered errors or drops.

1   An error occurred. For D program requests, an exit status of 1 indicates that program compilation failed or that the specified request could not be satisfied.

2   Invalid command line options or arguments were specified.

ENVIRONMENT VARIABLES

The following environment variables are consulted:

DTRACE_DEBUG
    Print libdtrace debugging output on standard error.

LIBCTF_DEBUG
    Print CTF type library debugging output on standard error.

DTRACE_OPT_*
    Set a given DTrace option. Options set this way are overridden both by options specified via -x on the command line, and by setopt statements.

DTRACE_MODULES_CONF
    The location of the file containing names of kernel modules to load (see below). If unset, /etc/dtrace-modules.

FILES

The following files are consulted:

/etc/dtrace-modules
    A list of kernel module names, one per line, which are loaded in addition to dtrace.ko if the dtrace device is not found. (Failure to load these modules is not an error.)

SEE ALSO
cpp(1), ssh(1)

Oracle Linux DTrace Guide

USAGE

When using the -p flag, dtrace stops the target processes while it is inspecting them and reporting results. A process can do nothing while it is stopped. This means that, if , for example, the X server is inspected by dtrace running in a window under the X server's control, the whole window system can become deadlocked, because the dtrace tool would be attempting to display its results to a window that cannot be refreshed. In such a case, logging in from another system using ssh(1) and killing the offending dtrace tool clears the deadlock.