stap(1) — Linux manual page


STAP(1)                  General Commands Manual                 STAP(1)

NAME         top

       stap - systemtap script translator/driver

SYNOPSIS         top

       stap [ OPTIONS ] - [ ARGUMENTS ]
       stap [ OPTIONS ] -e SCRIPT [ ARGUMENTS ]
       stap [ OPTIONS ] -l PROBE [ ARGUMENTS ]
       stap [ OPTIONS ] -L PROBE [ ARGUMENTS ]
       stap [ OPTIONS ] --dump-probe-types
       stap [ OPTIONS ] --dump-probe-aliases
       stap [ OPTIONS ] --dump-functions

DESCRIPTION         top

       The stap program is the front-end to the Systemtap tool.  It
       accepts probing instructions written in a simple domain-specific
       language, translates those instructions into C code, compiles
       this C code, and loads the resulting module into a running Linux
       kernel or a Dyninst user-space mutator, to perform the requested
       system trace/probe functions.  You can supply the script in a
       named file (FILENAME), from standard input (use - instead of
       FILENAME), or from the command line (using -e SCRIPT).  The
       program runs until it is interrupted by the user, or if the
       script voluntarily invokes the exit() function, or by sufficient
       number of soft errors.

       The language, which is described the SCRIPT LANGUAGE section
       below, is strictly typed, expressive, declaration free,
       procedural, prototyping-friendly, and inspired by awk and C.  It
       allows source code points or events in the system to be
       associated with handlers, which are subroutines that are executed
       synchronously.  It is somewhat similar conceptually to
       "breakpoint command lists" in the gdb debugger.


       systemtap comes with a variety of educational, documentation and
       reference resources.  They come online and/or packaged for
       offline use.  Some systemtap diagnostic warning/error messages
       specially suggest reading a man page by including a string like
       [man error::pass5].  For online documentation, see the project
       web site,

       │ man pages                 │                                                      │
       │ stap (this page)          │ language syntax, concepts, operation, options        │
       │ error::*                  │ further explanation of error conditions              │
       │ warning::*                │ further explanation of warning conditions            │
       │ stapprobes                │ probe points and their $context variables            │
       │ stapref                   │ quick reference to language syntax                   │
       │ stappaths                 │ list of directories, including books & references    │
       │ stap-prep                 │ program to install auxiliary dependencies like ker‐  │
       │                           │ nel debuginfo                                        │
       │ tapset::*                 │ generated list of tapsets                            │
       │ probe::*                  │ generated list of tapset probe aliases               │
       │ function::*               │ generated list of tapset functions                   │
       │ macro::*                  │ generated list of tapset macros                      │
       │ stapvars                  │ some of the tapset global variables                  │
       │ staprun, stapdyn, stapbpf │ programs for executing compiled systemtap scripts    │
       │ systemtap                 │ initscript, boot-time probing                        │
       │ stap-server               │ compilation server                                   │
       │ stapex                    │ a few very basic script examples                     │
       │ books                     │                                                      │
       │ Beginner's Guide          │ tutorial book, language essentials, examples         │
       │ Tutorial                  │ shorter tutorial, exercises                          │
       │ Language Reference        │ detailed language manual, covers statistics/analysis │
       │ Tapset Reference          │ the tapset man pages, reformatted into a book        │
       │ references                │                                                      │
       │ example scripts           │ over a hundred directly usable sysadmin tools, toys, │
       │                           │ hacks to learn from                                  │

OPTIONS         top

       The systemtap translator supports the following options.  Any
       other option prints a list of supported options.  Options may be
       given on the command line, as usual.  If the file $SYSTEM‐
       TAP_DIR/rc exist, options are also loaded from there and inter‐
       preted first.  ($SYSTEMTAP_DIR defaults to $HOME/.systemtap if

       In some cases, the default value of an option depends on particu‐
       lar system configuration and thus can't be mentioned here direct‐
       ly.  In some of those cases running "stap --help" might display
       the default.

       -      Use standard input instead of a given FILENAME as probe
              language input, unless -e SCRIPT is given.

       -h --help
              Show help message.

       -V --version
              Show version message.

       -p NUM Stop after pass NUM.  The passes are numbered 1-5: parse,
              elaborate, translate, compile, run.  See the PROCESSING
              section for details.

       -v     Increase verbosity for all passes.  Produce a larger vol‐
              ume of informative (?) output each time option repeated.

       --vp ABCDE
              Increase verbosity on a per-pass basis.  For example,
              "--vp 002" adds 2 units of verbosity to pass 3 only.  The
              combination "-v --vp 00004" adds 1 unit of verbosity for
              all passes, and 4 more for pass 5.

       -k     Keep the temporary directory after all processing.  This
              may be useful in order to examine the generated C code, or
              to reuse the compiled kernel object.

       -g     Guru mode.  Enable parsing of unsafe expert-level con‐
              structs like embedded C.

       -P     Prologue-searching mode.  This is equivalent to --pro‐
              logue-searching=always.  Activate heuristics to work
              around incorrect debugging information for function para‐
              meter $context variables.

       -u     Unoptimized mode.  Disable unused code elision and many
              other optimizations during elaboration / translation.

       -w     Suppressed warnings mode.  Disables all warning messages.

       -W     Treat all warnings as errors.

       -b     Use bulk mode (percpu files) for kernel-to-user data
              transfer.  Use the stap-merge program to multiplex them
              back together later.

       -i --interactive
              Interactive mode. Enable an interface to build the system‐
              tap script incrementally and interactively.

       -t     Collect timing information on the number of times probe
              executes and average amount of time spent in each probe-
              point. Also shows the derivation for each probe-point.

       -s NUM Use NUM megabyte buffers for kernel-to-user data transfer
              per processor.  The default is 16MB, or less on smaller
              memory machines.

       -I DIR Add the given directory to the tapset search directory.
              See the description of pass 2 for details.

       -D NAME=VALUE
              Add the given C preprocessor directive to the module Make‐
              file.  These can be used to override limit parameters de‐
              scribed below.

       -B NAME=VALUE
              In kernel-runtime mode, add the given make directive to
              the kernel module build's make invocation.  These can be
              used to add or override kconfig options.  For example, use

              -B CONFIG_DEBUG_INFO=y

              to add debugging information.

       -B FLAG
              In dyninst-runtime mode, add the given parameter to the
              compiler CFLAGS used for building the dyninst shared li‐
              brary.  For example, use

              -B -g

              to add debugging information.

       -a ARCH
              Use a cross-compilation mode for the given target archi‐
              tecture.  This requires access to the cross-compiler and
              the kernel build tree, and goes along with the

              -B CROSS_COMPILE=arch-tool-prefix-
              -r /build/tree


       --modinfo NAME=VALUE
              Add the name/value pair as a MODULE_INFO macro call to the
              generated module.  This may be useful to inform or over‐
              ride various module-related checks in the kernel.

       -G NAME=VALUE
              Sets the value of global variable NAME to VALUE when
              staprun is invoked.  This applies to scalar variables de‐
              clared global in the script/tapset.

       -R DIR Look for the systemtap runtime sources in the given direc‐
              tory.  Your DIR default can be seen using "stap --help".

       -r /DIR
              Build for kernel in given build tree. Can also be set with
              the SYSTEMTAP_RELEASE environment variable.

       -r RELEASE
              Build for kernel in build tree /lib/modules/RELEASE/build.
              Can also be set with the SYSTEMTAP_RELEASE environment

       -m MODULE
              Use the given name for the generated kernel object module,
              instead of a unique randomized name.  The generated kernel
              object module is copied to the current directory.

       -d MODULE
              Add symbol/unwind information for the given module into
              the kernel object module.  This may enable symbolic trace‐
              backs from those modules/programs, even if they do not
              have an explicit probe placed into them.

       --ldd  Add symbol/unwind information for all user-space shared
              libraries suspected by ldd to be necessary for user-space
              binaries being probed or listed with the -d option.  Cau‐
              tion: this can make the probe modules considerably larger.
              Note that this option does not deal with kernel-space mod‐
              ules: see instead --all-modules below.

              Equivalent to specifying "-dkernel" and a "-d" for each
              kernel module that is currently loaded.  Caution: this can
              make the probe modules considerably larger.

       -o FILE
              Send standard output to named file. In bulk mode, percpu
              files will start with FILE_ (FILE_cpu with -F) followed by
              the cpu number.  This supports strftime(3) formats for

       -c CMD Start the probes, run CMD, and exit when CMD finishes.
              This also has the effect of setting target() to the pid of
              that process.  Note that many probe types trigger indepen‐
              dently of this setting.  Consider including something like
              this to focus your script.

                 probe FOO { if (pid() != target()) next; .... }

       -x PID Sets target() to PID.  The script runs independently of
              the PID's lifespan.

       -e SCRIPT
              Run the given SCRIPT specified on the command line.

       -E SCRIPT
              Run the given SCRIPT specified. This SCRIPT is run in ad‐
              dition to the main script specified, through -e, or as a
              script file. This option can be repeated to run multiple
              scripts, and can be used in listing mode (-l/-L).

       -l PROBE
              Instead of running a probe script, just list all available
              probe points matching the given single probe point.  The
              pattern may include wildcards and aliases, but not comma-
              separated multiple probe points.  The process result code
              will indicate failure if there are no matches.

              % stap -e 'probe syscall.* { }'
              % stap -l 'syscall.*'

       -L PROBE
              Similar to "-l", but list matching probe points plus their
              available context variables.  When -v is set with -L, the
              output includes duplicate probe points which are distin‐
              guished by their PC address.

              % stap -L 'process("/lib64/libpython*.so.*").mark("*")'
              process("/usr/lib64/").mark("function__entry") $arg1:long $arg2:long $arg3:long
              process("/usr/lib64/").mark("function__return") $arg1:long $arg2:long $arg3:long
              process("/usr/lib64/").mark("function__entry") $arg1:long $arg2:long $arg3:long
              process("/usr/lib64/").mark("function__return") $arg1:long $arg2:long $arg3:long
              process("/usr/lib64/").mark("gc__done") $arg1:long
              process("/usr/lib64/").mark("gc__start") $arg1:long
              process("/usr/lib64/").mark("line") $arg1:long $arg2:long $arg3:long

       -F     Without -o option, load module and start probes, then de‐
              tach from the module leaving the probes running.  With -o
              option, run staprun in background as a daemon and show its

       -S size[,N]
              Sets the maximum size of output file and the maximum num‐
              ber of output files.  If the size of output file will ex‐
              ceed size megabytes, systemtap switches output file to the
              next file. And if the number of output files exceed N ,
              systemtap removes the oldest output file. You can omit the
              second argument.

       -T TIMEOUT
              Exit the script after TIMEOUT seconds.

              Ignore unresolvable or run-time-inaccessible context vari‐
              ables and substitute with 0, without errors.

              Prologue-searching mode. Activate heuristics to work
              around incorrect debugging information  for  function  pa‐
              rameter $context variables. WHEN can be either "never",
              "always", or "auto" (i.e. enabled by heuristic). If WHEN
              is missing, then "always" is assumed. If the option is
              missing, then "auto" is assumed.

              Wrap all probe handlers into something like this

              try { ... } catch { next }

              block, which causes any runtime errors to be quietly sup‐
              pressed.  Suppressed errors do not count against MAXERRORS
              limits.  In this mode, the MAXSKIPPED limits are also sup‐
              pressed, so that many errors and skipped probes may be ac‐
              cumulated during a script's runtime.  Any overall counts
              will still be reported at shutdown.

       --compatible VERSION
              Suppress recent script language or tapset changes which
              are incompatible with given older version of systemtap.
              This may be useful if a much older systemtap script fails
              to run.  See the DEPRECATION section for more details.

              This option is used to check if the active script has any
              constructs that may be systemtap version specific.  See
              the DEPRECATION section for more details.

              This option prunes stale entries from the cache directory.
              This is normally done automatically after successful runs,
              but this option will trigger the cleanup manually and then
              exit.  See the CACHING section for more details about
              cache limits.

       --color[=WHEN], --colour[=WHEN]
              This option controls coloring of error messages. WHEN can
              be either "never", "always", or "auto" (i.e. enable only
              if at a terminal). If WHEN is missing, then "always" is
              assumed. If the option is missing, then "auto" is assumed.

              Colors can be modified using the SYSTEMTAP_COLORS environ‐
              ment variable. The format must be of the form
              key1=val1:key2=val2:key3=val3 ...etc.  Valid keys are
              "error", "warning", "source", "caret", and "token".  Val‐
              ues constitute Select Graphic Rendition (SGR) parame‐
              ter(s). Consult the documentation of your terminal for the
              SGRs it supports. As an example, the default colors would
              be expressed as
              If SYSTEMTAP_COLORS is absent, the default colors will be
              used. If it is empty or invalid, coloring is turned off.

              This option disables all use of the cache directory.  No
              files will be either read from or written to the cache.

              This option treats files in the cache directory as in‐
              valid.  No files will be read from the cache, but result‐
              ing files from this run will still be written to the
              cache.  This is meant as a troubleshooting aid when stap's
              cached behavior seems to be misbehaving.  If it helped,
              there is a probably a bug in systemtap that the developers
              would like you to report.

       --privilege[=stapusr | =stapsys | =stapdev]
              This option instructs stap to examine the script looking
              for constructs which are not allowed for the specified
              privilege level (see UNPRIVILEGED USERS).  Compilation
              fails if any such constructs are used.  If stapusr or
              stapsys are specified when using a compile server (see
              --use-server), the server will examine the script and, if
              compilation succeeds, the server will cryptographically
              sign the resulting kernel module, certifying that is it
              safe for use by users at the specified privilege level.

              If --privilege has not been specified, -pN has not been
              specified with N < 5, and the invoking user is not root,
              and is not a member of the group stapdev, then stap will
              automatically add the appropriate --privilege option to
              the options already specified.

              This option is equivalent to --privilege=stapusr.

       --use-server[=HOSTNAME[:PORT] | =IP_ADDRESS[:PORT] | =CERT_SERI‐
              Specify compile-server(s) to be used for compilation
              and/or in conjunction with --list-servers and
              --trust-servers (see below) for listing. If no argument is
              supplied, then the default in unprivileged mode (see
              --privilege) is to select compatible servers which are
              trusted as SSL peers and as module signers and currently
              online. Otherwise the default is to select compatible
              servers which are trusted as SSL peers and currently on‐
              line.  --use-server may be specified more than once, in
              which case a list of servers is accumulated in the order
              specified. Servers may be specified by host name, ip ad‐
              dress, or by certificate serial number (obtained using
              --list-servers).  The latter is most commonly used when
              adding or revoking trust in a server (see --trust-servers
              below). If a server is specified by host name or ip ad‐
              dress, then an optional port number may be specified. This
              is useful for accessing servers which are not on the local
              network or to specify a particular server.

              IP addresses may be IPv4 or IPv6 addresses.

              If a particular IPv6 address is link local and exists on
              more than one interface, the intended interface may be
              specified by appending the address with a percent sign (%)
              followed by the intended interface name. For example,

              In order to specify a port number with an IPv6 address, it
              is necessary to enclose the IPv6 address in square brack‐
              ets ([]) in order to separate the port number from the
              rest of the address. For example,
              "[fe80::5eff:35ff:fe07:55ca]:5000" or

              If --use-server has not been specified, -pN has not been
              specified with N < 5, and the invoking user not root, is
              not a member of the group stapdev, but is a member of the
              group stapusr, then stap will automatically add
              --use-server to the options already specified.

              Instructs stap to retry compilation of a script using a
              compile server if compilation on the local host fails in a
              manner which suggests that it might succeed using a serv‐
              er.  If this option is not specified, the default is no.
              If no argument is provided, then the default is yes. Com‐
              pilation will be retried for certain types of errors (e.g.
              insufficient data or resources) which may not occur during
              re-compilation by a compile server. Compile servers will
              be selected automatically for the re-compilation attempt
              as if --use-server was specified with no arguments.

              Display the status of the requested SERVERS, where SERVERS
              is a comma-separated list of server attributes. The list
              of attributes is combined to filter the list of servers
              displayed. Supported attributes are:

              all    specifies all known servers (trusted SSL peers,
                     trusted module signers, online servers).

                     specifies servers specified using --use-server.

              online filters the output by retaining information about
                     servers which are currently online.

                     filters the output by retaining information about
                     servers which are trusted as SSL peers.

              signer filters the output by retaining information about
                     servers which are trusted as module signers (see

                     filters the output by retaining information about
                     servers which are compatible with the current ker‐
                     nel release and architecture.

              If no argument is provided, then the default is specified.
              If no servers were specified using --use-server, then the
              default servers for --use-server are listed.

              Note that --list-servers uses the avahi-daemon service to
              detect online servers. If this service is not available,
              then --list-servers will fail to detect any online
              servers. In order for --list-servers to detect servers
              listening on IPv6 addresses, the avahi-daemon configura‐
              tion file /etc/avahi/avahi-daemon.conf must contain an ac‐
              tive "use-ipv6=yes" line. The service must be restarted
              after adding this line in order for IPv6 to be enabled.

              Grant or revoke trust in compile-servers, specified using
              --use-server as specified by TRUST_SPEC, where TRUST_SPEC
              is a comma-separated list specifying the trust which is to
              be granted or revoked. Supported elements are:

              ssl    trust the specified servers as SSL peers.

              signer trust the specified servers as module signers (see
                     --privilege).  Only root can specify signer.

                     grant trust as an ssl peer for all users on the lo‐
                     cal host. The default is to grant trust as an ssl
                     peer for the current user only. Trust as a module
                     signer is always granted for all users. Only root
                     can specify all-users.

              revoke revoke the specified trust. The default is to grant

                     do not prompt the user for confirmation before car‐
                     rying out the requested action. The default is to
                     prompt the user for confirmation.

              If no argument is provided, then the default is ssl.  If
              no servers were specified using --use-server, then no
              trust will be granted or revoked.

              Unless no-prompt has been specified, the user will be
              prompted to confirm the trust to be granted or revoked be‐
              fore the operation is performed.

              Sign the module with a MOK (Machine Owner Key) on UEFI/Se‐
              cureBoot systems.  See the SECUREBOOT section for more de‐

              Dumps a list of supported probe types and exits. If
              --privilege=stapusr is also specified, the list will be
              limited to probe types available to unprivileged users.

              Dumps a list of all probe aliases found in library files
              and exits.

              Dumps a list of all the public functions found in library
              files and exits. Also includes their parameters and types.
              A function of type 'unknown' indicates a function that
              does not return a value. Note that not all function/para‐
              meter types may be resolved (these are also shown by 'un‐
              known'). This features is very memory-intensive and thus
              may not work properly with --use-server if the target
              server imposes an rlimit on process memory (i.e. through
              the ~stap-server/.systemtap/rc configuration file, see

       --remote URL
              Set the execution target to the given host.  This option
              may be repeated to target multiple execution targets.
              Passes 1-4 are completed locally as normal to build the
              script, and then pass 5 will copy the module to the target
              and run it.  Acceptable URL forms include:

              [USER@]HOSTNAME, ssh://[USER@]HOSTNAME
                     This mode uses ssh, optionally using a username not
                     matching your own. If a custom ssh_config file is
                     in use, add SendEnv LANG to retain international‐
                     ization functionality.

              libvirt://DOMAIN, libvirt://DOMAIN/LIBVIRT_URI
                     This mode uses stapvirt to execute the script on a
                     domain managed by libvirt. Optionally, LIBVIRT_URI
                     may be specified to connect to a specific driver
                     and/or a remote host. For example, to connect to
                     the local privileged QEMU driver, use:

                     --remote libvirt://MyDomain/qemu:///system

                     See the page at <> for
                     supported URIs. Also see stapvirt(1) for more in‐
                     formation on how to prepare the domain for stap

                     This mode connects to a UNIX socket. This can be
                     used with a QEMU virtio-serial port for executing
                     scripts inside a running virtual machine.

                     Special loopback mode to run on the local host.

              Prefix each line of remote output with "N: ", where N is
              the index of the remote execution target from which the
              given line originated.

              Enable, disable or set a timeout for the automatic debug‐
              info downloading feature offered by abrt as specified by
              OPTION, where OPTION is one of the following:

              yes    enable automatic downloading of debuginfo with no
                     timeout. This is the same as not providing an OP‐
                     TION value to --download-debuginfo

              no     explicitly disable automatic downloading of debug‐
                     info. This is the same as not using the option at

              ask    show abrt output, and ask before continuing down‐
                     load. No timeout will be set.

                     specify a timeout as a positive number to stop the
                     download if it is taking longer than <timeout> sec‐

              Specify the maximum size of the process's virtual memory
              (address space), in bytes.

              Specify the CPU time limit, in seconds.

              Specify the maximum number of processes that can be creat‐

              Specify the maximum size of the process stack, in bytes.

              Specify the maximum size of files that the process may
              create, in bytes.

              Specify sysroot directory where target files (executables,
              libraries, etc.)  are located.  With -r RELEASE, the sys‐
              root will be searched for the appropriate kernel build di‐
              rectory.  With -r /DIR, however, the sysroot will not be
              used to find the kernel build.

              Provide an alternate value for an environment variable
              where the value on a remote system differs.  Path vari‐
              ables (e.g. PATH, LD_LIBRARY_PATH) are assumed to be rela‐
              tive to the directory provided by --sysroot, if provided.

              Disable -DSTP_OVERLOAD related options as well as -DMAXAC‐
              TION and -DMAXTRYLOCK.  This option requires guru mode.

              Set the pass-5 runtime mode.  Valid options are kernel
              (default), dyninst and bpf.  See ALTERNATE RUNTIMES below
              for more information.

              Shorthand for --runtime=dyninst.

       --bpf  Shorthand for --runtime=bpf.

              On machines that require SystemTap to build its own up‐
              robes module (kernels prior to version 3.5), this option
              instructs SystemTap to also save a copy of the module in
              the current directory (creating a new "uprobes" directory

              Allow for a set of target namespaces to be set based on
              the namespaces the given PID is in. This is for name‐
              space-aware tapset functions. If the target namespaces was
              not set, the target defaults to the stap process' name‐

              Enables an interface to display status information about
              the module(uptime, module name, invoker uid, memory sizes,
              global variables, list of probes with their statistics).
              An optional argument INTERVAL can be supplied to set the
              refresh rate in seconds of the status window. The module
              can also be controlled by a list of commands using the
              following keys:

              c      Resets all global variables to their initial values
                     or zeroes them if they did not have an initial val‐

              s      Rotates the attribute used to sort the list of

              t      Brings up a prompt to allow toggling(on/off) of
                     probes by index. Probe points are still affected by
                     their conditions.

              r      Resumes the script by toggling on all probes.

              p      Pauses the script by toggling off all probes.

              x      Hides/shows the status window. This allows for more
                     output to be seen.

                     The navigation keys can be used to scroll up and
                     down the windows.

              Tab    Toggle scrolling between status and output windows.

              This option is used to run example scripts without having
              to enter the entire path to the script. Example scripts
              can be found in the directory specified in the
              stappaths(7) manual page.

              This option is used to disable the automatic logging of
              unused global variables at the end of a stap session.

              Language server mode. Start a language server which will
              communicate via stdio. The language server will respect
              stap verbosity.

              Execute passes 1-4 under specified user to increase safe‐
              ty.  This approach may have limitations.  Unprivileged
              users might not have access to kallsyms or /proc.  At the
              RPM install time, the stapunpriv user is created, so stap
              can be invoked with --build-as=stapunpriv.

ARGUMENTS         top

       Any additional arguments on the command line are passed to the
       script parser for substitution.  See below.


       The systemtap script language resembles awk and C.  There are two
       main outermost constructs: probes and functions.  Within these,
       statements and expressions use C-like operator syntax and prece‐

       Whitespace is ignored.  Three forms of comments are supported:
              # ... shell style, to the end of line, except for $# and
              // ... C++ style, to the end of line
              /* ... C style ... */
       Literals are either strings enclosed in double-quotes (passing
       through the usual C escape codes with backslashes, and with adja‐
       cent string literals glued together, also as in C), or integers
       (in decimal, hexadecimal, or octal, using the same notation as in
       C).  All strings are limited in length to some reasonable value
       (a few hundred bytes).  Integers are 64-bit signed quantities,
       although the parser also accepts (and wraps around) values above
       positive 2**63.

       In addition, script arguments given at the end of the command
       line may be inserted.  Use $1 ... $<NN> for insertion unquoted,
       @1 ... @<NN> for insertion as a string literal.  The number of
       arguments may be accessed through $# (as an unquoted number) or
       through @# (as a quoted number).  These may be used at any place
       a token may begin, including within the preprocessing stage.
       Reference to an argument number beyond what was actually given is
       an error.

       A simple conditional preprocessing stage is run as a part of
       parsing.  The general form is similar to the cond ? exp1 : exp2
       ternary operator:

              %( CONDITION %? TRUE-TOKENS %)
              %( CONDITION %? TRUE-TOKENS %: FALSE-TOKENS %)

       The CONDITION is either an expression whose format is determined
       by its first keyword, or a string literals comparison or a numer‐
       ic literals comparison.  It can be also composed of many alterna‐
       tives and conjunctions of CONDITIONs (meant as in previous sen‐
       tence) using || and && respectively.  However, parentheses are
       not supported yet, so remembering that conjunction takes prece‐
       dence over alternative is important.

       If the first part is the identifier kernel_vr or kernel_v to re‐
       fer to the kernel version number, with ("2.6.13-1.322FC3smp") or
       without ("2.6.13") the release code suffix, then the second part
       is one of the six standard numeric comparison operators <, <=,
       ==, !=, >, and >=, and the third part is a string literal that
       contains an RPM-style version-release value.  The condition is
       deemed satisfied if the version of the target kernel (as option‐
       ally overridden by the -r option) compares to the given version
       string.  The comparison is performed by the glibc function
       strverscmp.  As a special case, if the operator is for simple
       equality (==), or inequality (!=), and the third part contains
       any wildcard characters (* or ? or [), then the expression is
       treated as a wildcard (mis)match as evaluated by fnmatch.

       If, on the other hand, the first part is the identifier arch to
       refer to the processor architecture (as named by the kernel build
       system ARCH/SUBARCH), then the second part is one of the two
       string comparison operators == or !=, and the third part is a
       string literal for matching it.  This comparison is a wildcard

       Similarly, if the first part is an identifier like CONFIG_some‐
       thing to refer to a kernel configuration option, then the second
       part is == or !=, and the third part is a string literal for
       matching the value (commonly "y" or "m").  Nonexistent or unset
       kernel configuration options are represented by the empty string.
       This comparison is also a wildcard (mis)match.

       If the first part is the identifier systemtap_v, the test refers
       to the systemtap compatibility version, which may be overridden
       for old scripts with the --compatible flag.  The comparison oper‐
       ator is as is for kernel_v and the right operand is a version
       string.  See also the DEPRECATION section below.

       If the first part is the identifier systemtap_privilege, the test
       refers to the privilege level that the systemtap script is com‐
       piled with. Here the second part is == or !=, and the third part
       is a string literal, either "stapusr" or "stapsys" or "stapdev".

       If the first part is the identifier guru_mode, the test refers to
       if the systemtap script is compiled with guru_mode. Here the sec‐
       ond part is == or !=, and the third part is a number, either 1 or

       If the first part is the identifier runtime, the test refers to
       the systemtap runtime mode. See ALTERNATE RUNTIMES below for more
       information on runtimes.  The second part is one of the two
       string comparison operators == or !=, and the third part is a
       string literal for matching it.  This comparison is a wildcard

       Otherwise, the CONDITION is expected to be a comparison between
       two string literals or two numeric literals.  In this case, the
       arguments are the only variables usable.

       The TRUE-TOKENS and FALSE-TOKENS are zero or more general parser
       tokens (possibly including nested preprocessor conditionals), and
       are passed into the input stream if the condition is true or
       false.  For example, the following code induces a parse error un‐
       less the target kernel version is newer than 2.6.5:

              %( kernel_v <= "2.6.5" %? **ERROR** %) # invalid token sequence

       The following code might adapt to hypothetical kernel version

              probe kernel.function (
                %( kernel_v <= "2.6.12" %? "__mm_do_fault" %:
                   %( kernel_vr == "2.6.13*smp" %? "do_page_fault" %:
                      UNSUPPORTED %) %)
              ) { /* ... */ }

              %( arch == "ia64" %?
                 probe syscall.vliw = kernel.function("vliw_widget") {}

       The preprocessor also supports a simple macro facility, run as a
       separate pass before conditional preprocessing.

       Macros are defined using the following construct:

              @define NAME %( BODY %)
              @define NAME(PARAM_1, PARAM_2, ...) %( BODY %)

       Macros, and parameters inside a macro body, are both invoked by
       prefixing the macro name with an @ symbol:

              @define foo %( x %)
              @define add(a,b) %( ((@a)+(@b)) %)

                 @foo = @add(2,2)

       Macro expansion is currently performed in a separate pass before
       conditional compilation. Therefore, both TRUE- and FALSE-tokens
       in conditional expressions will be macroexpanded regardless of
       how the condition is evaluated. This can sometimes lead to er‐

              // The following results in a conflict:
              %( CONFIG_UPROBE == "y" %?
                  @define foo %( process.syscall %)
                  @define foo %( **ERROR** %)

              // The following works properly as expected:
              @define foo %(
                %( CONFIG_UPROBE == "y" %? process.syscall %: **ERROR** %)

       The first example is incorrect because both @defines are evaluat‐
       ed in a pass prior to the conditional being evaluated.

       Normally, a macro definition is local to the file it occurs in.
       Thus, defining a macro in a tapset does not make it available to
       the user of the tapset. Publically available library macros can
       be defined by including .stpm files on the tapset search path.
       These files may only contain @define constructs, which become
       visible across all tapsets and user scripts. Optionally, within
       the .stpm files, a public macro definition can be surrounded by a
       preprocessor conditional as described above.

       Tapsets or guru-mode user scripts can access header file constant
       tokens, typically macros, using built-in @const() operator.  The
       respective header file inclusion is possible either via the
       tapset library, or using a top-level guru mode embedded-C con‐
       struct.  This results in appropriate embedded C pragma comments


       Identifiers for variables and functions are an alphanumeric se‐
       quence, and may include _ and $ characters.  They may not start
       with a plain digit, as in C.  Each variable is by default local
       to the probe or function statement block within which it is men‐
       tioned, and therefore its scope and lifetime is limited to a par‐
       ticular probe or function invocation.

       Scalar variables are implicitly typed as either string or inte‐
       ger.  Associative arrays also have a string or integer value, and
       a tuple of strings and/or integers serving as a key.  Here are a
       few basic expressions.

              var1 = 5
              var2 = "bar"
              array1 [pid()] = "name"     # single numeric key
              array2 ["foo",4,i++] += 5   # vector of string/num/num keys
              if (["hello",5,4] in array2) println ("yes")  # membership test

       The translator performs type inference on all identifiers, in‐
       cluding array indexes and function parameters.  Inconsistent
       type-related use of identifiers signals an error.

       Variables may be declared global, so that they are shared amongst
       all probes and functions and live as long as the entire systemtap
       session.  There is one namespace for all global variables, re‐
       gardless of which script file they are found within.  Concurrent
       access to global variables is automatically protected with locks,
       see the SAFETY AND SECURITY section for more details.  A global
       declaration may be written at the outermost level anywhere, not
       within a block of code.  Global variables which are written but
       never read will be displayed automatically at session shutdown.
       The translator will infer for each its value type, and if it is
       used as an array, its key types.  Optionally, scalar globals may
       be initialized with a string or number literal.  The following
       declaration marks variables as global.

              global var1, var2, var3=4

       Global variables can also be set as module options. One can do
       this by either using the -G option, or the module must first be
       compiled using stap -p4.  Global variables can then be set on the
       command line when calling staprun on the module generated by stap
       -p4. See staprun(8) for more information.

       The scope of a global variable may be limited to a tapset or user
       script file using private keyword. The global keyword is optional
       when defining a private global variable. Following declaration
       marks var1 and var2 private globals.

              private global var1=2
              private var2

       Arrays are limited in size by the MAXMAPENTRIES variable -- see
       the SAFETY AND SECURITY section for details.  Optionally, global
       arrays may be declared with a maximum size in brackets, overrid‐
       ing MAXMAPENTRIES for that array only.  Note that this doesn't
       indicate the type of keys for the array, just the size.

              global tiny_array[10], normal_array, big_array[50000]

       Arrays may be configured for wrapping using the '%' suffix.  This
       causes older elements to be overwritten if more elements are in‐
       serted than the array can hold. This works for both associative
       and statistics typed arrays.

              global wrapped_array1%[10], wrapped_array2%

       Many types of probe points provide context variables, which are
       run-time values, safely extracted from the kernel or userspace
       program being probed.  These are prefixed with the $ character.
       The CONTEXT VARIABLES section in stapprobes(3stap) lists what is
       available for each type of probe point.  These context variables
       become normal string or numeric scalars once they are stored in
       normal script variables.  See the TYPECASTING section below on
       how to to turn them back into typed pointers for further process‐
       ing as context variables.  There is some automation to help!

       Statements enable procedural control flow.  They may occur within
       functions and probe handlers.  The total number of statements ex‐
       ecuted in response to any single probe event is limited to some
       number defined by the MAXACTION macro in the translated C code,
       and is in the neighbourhood of 1000.

       EXP    Execute the string- or integer-valued expression and throw
              away the value.

       { STMT1 STMT2 ... }
              Execute each statement in sequence in this block.  Note
              that separators or terminators are generally not necessary
              between statements.

       ;      Null statement, do nothing.  It is useful as an optional
              separator between statements to improve syntax-error de‐
              tection and to handle certain grammar ambiguities.

       if (EXP) STMT1 [ else STMT2 ]
              Compare integer-valued EXP to zero.  Execute the first
              (non-zero) or second STMT (zero).

       while (EXP) STMT
              While integer-valued EXP evaluates to non-zero, execute

       for (EXP1; EXP2; EXP3) STMT
              Execute EXP1 as initialization.  While EXP2 is non-zero,
              execute STMT, then the iteration expression EXP3.

       foreach (VAR in ARRAY [ limit EXP ]) STMT
              Loop over each element of the named global array, assign‐
              ing current key to VAR.  The array may not be modified
              within the statement.  By adding a single + or - operator
              after the VAR or the ARRAY identifier, the iteration will
              proceed in a sorted order, by ascending or descending in‐
              dex or value.  If the array contains statistics aggre‐
              gates, adding the desired @operator between the ARRAY
              identifier and the + or - will specify the sorting aggre‐
              gate function.  See the STATISTICS section below for the
              ones available.  Default is @count.  Using the optional
              limit keyword limits the number of loop iterations to EXP
              times.  EXP is evaluated once at the beginning of the

       foreach ([VAR1, VAR2, ...] in ARRAY [ limit EXP ]) STMT
              Same as above, used when the array is indexed with a tuple
              of keys.  A sorting suffix may be used on at most one VAR
              or ARRAY identifier.

       foreach ([VAR1, VAR2, ...] in ARRAY [INDEX1, INDEX2, ...] [ limit
       EXP ]) STMT
              Same as above, where iterations are limited to elements in
              the array where the keys match the index values specified.
              The symbol * can be used to specify an index and will be
              treated as a wildcard.

       foreach (VAR0 = VAR in ARRAY [ limit EXP ]) STMT
              This variant of foreach saves current value into VAR0 on
              each iteration, so it is the same as ARRAY[VAR].  This al‐
              so works with a tuple of keys.  Sorting suffixes on VAR0
              have the same effect as on ARRAY.

       foreach (VAR0 = VAR in ARRAY [INDEX1, INDEX2, ...] [ limit EXP ])
              Same as above, where iterations are limited to elements in
              the array where the keys match the index values specified.
              The symbol * can be used to specify an index and will be
              treated as a wildcard.

       break, continue
              Exit or iterate the innermost nesting loop (while or for
              or foreach) statement.

       return EXP
              Return EXP value from enclosing function.  If the func‐
              tion's value is not taken anywhere, then a return state‐
              ment is not needed, and the function will have a special
              "unknown" type with no return value.

       next   Return now from enclosing probe handler.  This is espe‐
              cially useful in probe aliases that apply event filtering
              predicates. When used in functions, the execution will be
              immediately transferred to the next overloaded function.

       try { STMT1 } catch { STMT2 }
              Run the statements in the first block.  Upon any run-time
              errors, abort STMT1 and start executing STMT2.  Any errors
              in STMT2 will propagate to outer try/catch blocks, if any.

       try { STMT1 } catch(VAR) { STMT2 }
              Same as above, plus assign the error message to the string
              scalar variable VAR.

       delete ARRAY[INDEX1, INDEX2, ...]
              Remove from ARRAY the element specified by the index tu‐
              ple.  If the index tuple contains a * in place of an in‐
              dex, the * is treated as a wildcard and all elements with
              keys that match the index tuple will be removed from AR‐
              RAY.  The value will no longer be available, and subse‐
              quent iterations will not report the element.  It is not
              an error to delete an element that does not exist.

       delete ARRAY
              Remove all elements from ARRAY.

       delete SCALAR
              Removes the value of SCALAR.  Integers and strings are
              cleared to 0 and "" respectively, while statistics are re‐
              set to the initial empty state.

       Systemtap supports a number of operators that have the same gen‐
       eral syntax, semantics, and precedence as in C and awk.  Arith‐
       metic is performed as per typical C rules for signed integers.
       Division by zero or overflow is detected and results in an error.

       binary numeric operators
              * / % + - >> << & ^ | && ||

       binary string operators
              .  (string concatenation)

       numeric assignment operators
              = *= /= %= += -= >>= <<= &= ^= |=

       string assignment operators
              = .=

       unary numeric operators
              + - ! ~ ++ --

       binary numeric, string comparison or regex matching operators
              < > <= >= == != =~ !~

       ternary operator
              cond ? exp1 : exp2

       grouping operator
              ( exp )

       function call
              fn ([ arg1, arg2, ... ])

       array membership check
              exp in array
              [exp1, exp2, ... ] in array
              [*, *, ... ] in array

       The scripting language supports regular expression matching.  The
       basic syntax is as follows:

              exp =~ regex
              exp !~ regex

       (The first operand must be an expression evaluating to a string;
       the second operand must be a string literal containing a syntac‐
       tically valid regular expression.)

       The regular expression syntax supports POSIX Extended Regular Ex‐
       pression features as documented in grep(1) except for subexpres‐
       sion reuse ("\1") functionality.

       After a successful match, the contents of the matched string and
       subexpressions can be extracted using the matched() and ngroups()
       tapset functions as follows:

              if ("an example string" =~ "str(ing)") {
                matched(0) // -> returns "string", the matched substring
                matched(1) // -> returns "ing", the 1st matched subexpression
                ngroups()  // -> returns 2, the number of matched groups

       The main construct in the scripting language identifies probes.
       Probes associate abstract events with a statement block ("probe
       handler") that is to be executed when any of those events occur.
       The general syntax is as follows:

              probe PROBEPOINT [, PROBEPOINT] { [STMT ...] }
              probe PROBEPOINT [, PROBEPOINT] if (CONDITION) { [STMT ...] }

       Events are specified in a special syntax called "probe points".
       There are several varieties of probe points defined by the trans‐
       lator, and tapset scripts may define further ones using aliases.
       Probe points may be wildcarded, grouped, or listed in preference
       sequences, or declared optional.  More details on probe point
       syntax and semantics are listed on the stapprobes(3stap) manual

       The probe handler is interpreted relative to the context of each
       event.  For events associated with kernel code, this context may
       include variables defined in the source code at that spot.  These
       "context variables" are presented to the script as variables
       whose names are prefixed with "$".  They may be accessed only if
       the kernel's compiler preserved them despite optimization.  This
       is the same constraint that a debugger user faces when working
       with optimized code.  In addition, the objects must exist in
       paged-in memory at the moment of the systemtap probe handler's
       execution, because systemtap must not cause (suppresses) any ad‐
       ditional paging.  Some probe types have very little context.  See
       the stapprobes(3stap) man pages to see the kinds of context vari‐
       ables available at each kind of probe point.  As of systemtap
       version 4.3, functions called from the handlers of some probe
       point types may also refer to context variables.  These are
       treated as if a clone of that function was inlined into the call‐
       ing probe handler and $variables evaluated in its context.

       Probes may be decorated with an arming condition, consisting of a
       simple boolean expression on read-only global script variables.
       While disarmed (inactive, condition evaluates to false), some
       probe types reduce or eliminate their run-time overheads.  When
       an arming condition evaluates to true, probes will be soon re-
       armed, and their probe handlers will start getting called as the
       events fire.  (Some events may be lost during the arming inter‐
       val.  If this is unacceptable, do not use arming conditions for
       those probes.)  Example of the syntax:

              probe if (enabled) {

       New probe points may be defined using "aliases".  Probe point
       aliases look similar to probe definitions, but instead of acti‐
       vating a probe at the given point, it just defines a new probe
       point name as an alias to an existing one. There are two types of
       alias, i.e. the prologue style and the epilogue style which are
       identified by "=" and "+=" respectively.

       For prologue style alias, the statement block that follows an
       alias definition is implicitly added as a prologue to any probe
       that refers to the alias. While for the epilogue style alias, the
       statement block that follows an alias definition is implicitly
       added as an epilogue to any probe that refers to the alias.  For

              probe = kernel.function("sys_read") {
                fildes = $fd
                if (execname() == "init") next  # skip rest of probe

       defines a new probe point, which expands to
       kernel.function("sys_read"), with the given statement as a pro‐
       logue, which is useful to predefine some variables for the alias
       user and/or to skip probe processing entirely based on some con‐
       ditions.  And

              probe += kernel.function("sys_read") {
                if (tracethis) println ($fd)

       defines a new probe point with the given statement as an epi‐
       logue, which is useful to take actions based upon variables set
       or left over by the the alias user.  Please note that in each
       case, the statements in the alias handler block are treated ordi‐
       narily, so that variables assigned there constitute mere initial‐
       ization, not a macro substitution.

       Aliases can also be defined to include both a prologue and an

              probe = kernel.function("sys_read") {
                fildes = $fd
                if (execname() == "init") next
                if (tracethis) println ($fd)

       An alias is used just like a built-in probe type.

              probe {
                printf("reading fd=%d\n", fildes)
                if (fildes > 10) tracethis = 1

       Probes with an alias can make use of the @probewrite predicate.
       This check is used to detect whether a script variable or target
       variable has been written to in the probe handler body.

              expands to 1 iff var has been written to in the probe han‐
              dler body, otherwise it expands to 0.

       In the following example, @probewrite(var) expands to 1 because
       var has been written to in the probe handler body and consequent‐
       ly, the conditional statement will run.

              probe foo = begin { var = 0 }, { if (@probewrite(var)) println(var) }

              probe foo {
                var = 1

       Systemtap scripts may define subroutines to factor out common
       work.  Functions take any number of scalar (integer or string)
       arguments, and must return a single scalar (integer or string).
       An example function declaration looks like this:

              function thisfn (arg1, arg2) {
                 return arg1 + arg2

       Note the general absence of type declarations, which are instead
       inferred by the translator.  However, if desired, a function def‐
       inition may include explicit type declarations for its return
       value and/or its arguments.  This is especially helpful for em‐
       bedded-C functions.  In the following example, the type inference
       engine need only infer type type of arg2 (a string).

              function thatfn:string (arg1:long, arg2) {
                 return sprint(arg1) . arg2

       Functions may call others or themselves recursively, up to a
       fixed nesting limit.  This limit is defined by the MAXNESTING
       macro in the translated C code and is in the neighbourhood of 10.

       Functions may be marked private using the private keyword to lim‐
       it their scope to the tapset or user script file they are defined
       in. An example definition of a private function follows:

              private function three:long () { return 3 }

       Functions terminating without reaching an explicit return state‐
       ment will return an implicit 0 or "", determined by type infer‐

       Functions may be overloaded during both runtime and compile time.

       Runtime overloading allows the executed function to be selected
       while the module is running based on runtime conditions and is
       achieved using the "next" statement in script functions and
       STAP_NEXT macro for embedded-C functions. For example,

              function f() { if (condition) next; print("first function") }
              function f() %{ STAP_NEXT; print("second function") %}
              function f() { print("third function") }

       During a functioncall f(), the execution will transfer to the
       third function if condition evaluates to true and print "third
       function". Note that the second function is unconditionally

       Parameter overloading allows the function to be executed to be
       selected at compile time based on the number of arguments provid‐
       ed to the functioncall. For example,

              function g() { print("first function") }
              function g(x) { print("second function") }
              g() -> "first function"
              g(1) -> "second function"

       Note that runtime overloading does not occur in the above exam‐
       ple, as exactly one function will be resolved for the function‐
       call. The use of a next statement inside a function while no more
       overloads remain will trigger a runtime exception Runtime over‐
       loading will only occur if the functions have the same arity,
       functions with the same name but different number of parameters
       are completely unrelated.

       Execution order is determined by a priority value which may be
       specified.  If no explicit priority is specified, user script
       functions are given a higher priority than library functions.
       User script functions and library functions are assigned a de‐
       fault priority value of 0 and 1 respectively.  Functions with the
       same priority are executed in declaration order. For example,

              function f():3 { if (condition) next; print("first function") }
              function f():1 { if (condition) next; print("second function") }
              function f():2 { print("third function") }

       Since the second function has highest priority, it is executed
       first.  The first function is never executed as there no "next"
       statements in the third function to transfer execution.

       There are a set of function names that are specially treated by
       the translator.  They format values for printing to the standard
       systemtap output stream in a more convenient way (note that data
       generated in the kernel module need to get transferred to user-
       space in order to get printed).

         The sprint* variants return the formatted string instead of
       printing it.

       print, sprint
              Print one or more values of any type, concatenated direct‐
              ly together.

       println, sprintln
              Print values like print and sprint, but also append a new‐

       printd, sprintd
              Take a string delimiter and two or more values of any
              type, and print the values with the delimiter interposed.
              The delimiter must be a literal string constant.

       printdln, sprintdln
              Print values with a delimiter like printd and sprintd, but
              also append a newline.

       printf, sprintf
              Take a formatting string and a number of values of corre‐
              sponding types, and print them all.  The format must be a
              literal string constant.

       The printf formatting directives similar to those of C, except
       that they are fully type-checked by the translator:

              %b     Writes a binary blob of the value given, instead of
                     ASCII text.  The width specifier determines the
                     number of bytes to write; valid specifiers are %b
                     %1b %2b %4b %8b.  Default (%b) is 8 bytes.

              %c     Character.

              %d,%i  Signed decimal.

              %m     Safely reads kernel (without #) or user (with #)
                     memory at the given address, outputs its content.
                     The optional precision specifier (not field width)
                     determines the number of bytes to read - default is
                     1 byte.  %10.4m prints 4 bytes of the memory in a
                     10-character-wide field.  Note, on some architec‐
                     tures user memory can still be read without #.

              %M     Same as %m, but outputs in hexadecimal.  The mini‐
                     mal size of output is double the optional precision
                     specifier - default is 1 byte (2 hex chars).
                     %10.4M prints 4 bytes of the memory as 8 hexadeci‐
                     mal characters in a 10-character-wide field.   %.*M
                     hex-dumps a given number of bytes from a given

              %o     Unsigned octal.

              %p     Unsigned pointer address.

              %s     String.

              %u     Unsigned decimal.

              %x     Unsigned hex value, in all lower-case.

              %X     Unsigned hex value, in all upper-case.

              %%     Writes a %.

       The # flag selects the alternate forms.  For octal, this prefixes
       a 0.  For hex, this prefixes 0x or 0X, depending on case.  For
       characters, this escapes non-printing values with either C-like
       escapes or raw octal.  In the case of %#m/%#M, this safely ac‐
       cesses user space memory rather than kernel space memory.


              a = "alice", b = "bob", p = 0x1234abcd, i = 123, j = -1, id[a] = 1234, id[b] = 4567
                   Prints: hello
                   Prints: bob\n
              println(a . " is " . sprint(16))
                   Prints: alice is 16
              foreach (name in id)  printdln("|", strlen(name), name, id[name])
                   Prints: 5|alice|1234\n3|bob|4567
              printf("%c is %s; %x or %X or %p; %d or %u\n",97,a,p,p,p,j,j)
                   Prints: a is alice; 1234abcd or 1234ABCD or 0x1234abcd; -1 or 18446744073709551615\n
              printf("2 bytes of kernel buffer at address %p: %2m", p, p)
                   Prints: 2 byte of kernel buffer at address 0x1234abcd: <binary data>
              printf("%4b", p)
                   Prints (these values as binary data): 0x1234abcd
              printf("%#o %#x %#X\n", 1, 2, 3)
                   Prints: 01 0x2 0X3
              printf("%#c %#c %#c\n", 0, 9, 42)
                   Prints: \000 \t *

       It is often desirable to collect statistics in a way that avoids
       the penalties of repeatedly exclusive locking the global vari‐
       ables those numbers are being put into.  Systemtap provides a so‐
       lution using a special operator to accumulate values, and several
       pseudo-functions to extract the statistical aggregates.

       The aggregation operator is <<<, and resembles an assignment, or
       a C++ output-streaming operation.  The left operand specifies a
       scalar or array-index lvalue, which must be declared global.  The
       right operand is a numeric expression.  The meaning is intuitive:
       add the given number to the pile of numbers to compute statistics
       of.  (The specific list of statistics to gather is given sepa‐
       rately, by the extraction functions.)

              foo <<< 1
              stats[pid()] <<< memsize

       The extraction functions are also special.  For each appearance
       of a distinct extraction function operating on a given identifi‐
       er, the translator arranges to compute a set of statistics that
       satisfy it.  The statistics system is thereby "on-demand".  Each
       execution of an extraction function causes the aggregation to be
       computed for that moment across all processors.

       Here is the set of extractor functions.  The first argument of
       each is the same style of lvalue used on the left hand side of
       the accumulate operation.  The @count(v), @sum(v), @min(v),
       @max(v), @avg(v), @variance(v[, b]) extractor functions compute
       the number/total/minimum/maximum/average/variance of all accumu‐
       lated values.  The resulting values are all simple integers.  Ar‐
       rays containing aggregates may be sorted and iterated.  See the
       foreach construct above.

       Variance uses Welford's online algorithm.  The calculations are
       based on integer arithmetic, and so may suffer from low precision
       and overflow.  To improve this, @variance(v[, b]) accepts an op‐
       tional parameter b, the bit-shift, ranging from 0 (default) to
       62, for internal scaling.  Only one value of bit-shift may be
       used with given global variable.  A larger bitshift value in‐
       creases precision, but increases the likelihood of overflow.

              $ stap -e \
              > 'global x probe oneshot { for(i=1;i<=5;i++) x<<<i println(@variance(x)) }'
              $ stap -e \
              > 'global x probe oneshot { for(i=1;i<=5;i++) x<<<i println(@variance(x,1)) }'
              $ python3 -c 'import statistics; print(statistics.variance([1, 2, 3, 4, 5]))'

       Overflow (from internal multiplication of large numbers) may oc‐
       cur and may cause a negative variance result.  Consider normaliz‐
       ing your input data.  Adding or subtracting a fixed value from
       all variance inputs preserves the original variance.  Dividing
       the variance inputs by a fixed value shrinks the original vari‐
       ance by that value squared.

       Histograms are also available, but are more complicated because
       they have a vector rather than scalar value.  @hist_lin‐
       ear(v,start,stop,interval) represents a linear histogram from
       "start" to "stop" (inclusive) by increments of "interval".  The
       interval must be positive. Similarly, @hist_log(v) represents a
       base-2 logarithmic histogram. Printing a histogram with the print
       family of functions renders a histogram object as a tabular
       "ASCII art" bar chart.

              probe timer.profile {
                x[1] <<< pid()
                x[2] <<< uid()
                y <<< tid()
              global x // an array containing aggregates
              global y // a scalar
              probe end {
                foreach ([i] in x @count+) {
                   printf ("x[%d]: avg %d = sum %d / count %d\n",
                           i, @avg(x[i]), @sum(x[i]), @count(x[i]))
                   println (@hist_log(x[i]))
                println ("y:")
                println (@hist_log(y))

       The counts of each histogram bucket may be individually accessed
       via the [index] operator.  Each bucket is addressed from 1
       through N (for each natural bucket).  In addition bucket #0
       counts all the samples beneath the start value, and bucket #N+1
       counts all the samples above the stop value.  Histogram buckets
       (including the two out-of-range buckets) may also be iterated
       with foreach.

              global x
              probe oneshot {
                x <<< -100
                x <<< 1
                x <<< 2
                x <<< 3
                x <<< 100
                foreach (bucket in @hist_linear(x,1,3,1))
                  // expecting   1 out-of-range-low bucket
                  //             3 payload buckets
                  //             1 out-of-range-high bucket
                  printf("bucket %d count %d\n",
                         bucket, @hist_linear(x,1,3,1)[bucket])

       Once a pointer (see the CONTEXT VARIABLES section of
       stapprobes(3stap)) has been saved into a script integer variable,
       the translator attempts to keep the type information necessary to
       access members from that pointer.

       The translator attempts to track DWARF typing associated with
       script variables assigned from addresses of context $variables,
       @cast or @var operators.  Depending on the complexity of the
       script code, this association may pass to related variables, so
       that -> and [] operators may be used on them, just as on the
       original context variable.  For example:

              foo = $param->foo; printf("x:%d y:%d\n", foo->x, foo->y)
              printf("my value is %d\n", ($type == 42 ? $foo : $bar)->value)
              printf("my parent pid is %d\n", task_parent(task_current())->tgid)

       However, if this association heuristic doesn't work for a script,
       using the @cast() operator tells the translator how to interpret
       the number as a typed pointer.

              @cast(p, "type_name"[, "module"])->member

       This will interpret p as a pointer to a struct/union named
       type_name and dereference the member value.  Further ->subfield
       expressions may be appended to dereference more levels. Note that
       for direct dereferencing of a pointer {ker‐
       nel,user}_{char,int,...}($p) should be used.  (Refer to stap‐
       funcs(5) for more details.)  NOTE: the same dereferencing opera‐
       tor -> is used to refer to both direct containment or pointer in‐
       direction.  Systemtap automatically determines which.  The op‐
       tional module tells the translator where to look for information
       about that type.  Multiple modules may be specified as a list
       with : separators.  If the module is not specified, it will de‐
       fault either to the probe module for dwarf probes, or to "kernel"
       for functions and all other probes types.

       Previously up to systemtap version 4.2, "kernel" was inferred if
       unspecified.  Use --compatible=4.2 to activate this default.

       The translator can create its own module with type information
       from a header surrounded by angle brackets, in case normal debug‐
       info is not available.  For kernel headers, prefix it with "ker‐
       nel" to use the appropriate build system.  All other headers are
       built with default GCC parameters into a user module.  Multiple
       headers may be specified in sequence to resolve a codependency.

              @cast(tv, "timeval", "<sys/time.h>")->tv_sec
              @cast(task, "task_struct", "kernel<linux/sched.h>")->tgid
              @cast(task, "task_struct",

       Values acquired by @cast may be pretty-printed by the $ and $$
       suffix operators, the same way as described in the CONTEXT VARI‐
       ABLES section of the stapprobes(3stap) manual page.

       When in guru mode, the translator will also allow scripts to as‐
       sign new values to members of typecasted pointers.

       Typecasting is also useful in the case of void* members whose
       type may be determinable at runtime.

              probe foo {
                if ($var->type == 1) {
                  value = @cast($var->data, "type1")->bar
                } else {
                  value = @cast($var->data, "type2")->baz

       When in guru mode, the translator accepts embedded C code in the
       top level of the script.  Such code is enclosed between %{ and %}
       markers, and is transcribed verbatim, without analysis, in some
       sequence, into the top level of the generated C code.  At the
       outermost level, this may be useful to add #include instructions,
       and any auxiliary definitions for use by other embedded code.

       Another place where embedded code is permitted is as a function
       body.  In this case, the script language body is replaced entire‐
       ly by a piece of C code enclosed again between %{ and %} markers.
       This C code may do anything reasonable and safe.  There are a
       number of undocumented but complex safety constraints on atomici‐
       ty, concurrency, resource consumption, and run time limits, so
       this is an advanced technique.

       The memory locations set aside for input and output values are
       made available to it using macros STAP_ARG_* and STAP_RETVALUE.
       Errors may be signalled with STAP_ERROR. Output may be written
       with STAP_PRINTF. The function may return early with STAP_RETURN.
       Here are some examples:

              function integer_ops (val) %{
                STAP_PRINTF("%d\n", STAP_ARG_val);
                STAP_RETVALUE = STAP_ARG_val + 1;
                if (STAP_RETVALUE == 4)
                    STAP_ERROR("wrong guess: %d", (int) STAP_RETVALUE);
                if (STAP_RETVALUE == 3)
                STAP_RETVALUE ++;
              function string_ops (val) %{
                strlcpy (STAP_RETVALUE, STAP_ARG_val, MAXSTRINGLEN);
                strlcat (STAP_RETVALUE, "one", MAXSTRINGLEN);
                if (strcmp (STAP_RETVALUE, "three-two-one"))
                    STAP_RETURN("parameter should be three-two-");
              function no_ops () %{
                  STAP_RETURN(); /* function inferred with no return value */

       The function argument and return value types have to be inferred
       by the translator from the call sites in order for this to work.
       The user should examine C code generated for ordinary script-lan‐
       guage functions in order to write compatible embedded-C ones.

       The last place where embedded code is permitted is as an expres‐
       sion rvalue.  In this case, the C code enclosed between %{ and %}
       markers is interpreted as an ordinary expression value.  It is
       assumed to be a normal 64-bit signed number, unless the marker /*
       string */ is included, in which case it's treated as a string.

              function add_one (val) {
                return val + %{ 1 %}
              function add_string_two (val) {
                return val . %{ /* string */ "two" %}
              @define SOME_STAP_MACRO %( %{ SOME_C_MACRO %} %)
              probe begin {
                    printf("SOME_C_MACRO has value: %d\n", @SOME_STAP_MACRO);

       The embedded-C code may contain markers to assert optimization
       and safety properties.

       /* pure */
              means that the C code has no side effects and may be elid‐
              ed entirely if its value is not used by script code.

       /* stable */
              means that the C code always has the same value (in any
              given probe handler invocation), so repeated calls may be
              automatically replaced by memoized values.  Such functions
              must take no parameters, and also be pure.

       /* unprivileged */
              means that the C code is so safe that even unprivileged
              users are permitted to use it.

       /* myproc-unprivileged */
              means that the C code is so safe that even unprivileged
              users are permitted to use it, provided that the target of
              the current probe is within the user's own process.

       /* guru */
              means that the C code is so unsafe that a systemtap user
              must specify -g (guru mode) to use this.  (Tapsets are
              permitted and presumed to call them safely.)

       /* unmangled */
              in an embedded-C function, means that the legacy (pre-1.8)
              argument access syntax should be made available inside the
              function. Hence, in addition to STAP_ARG_foo and STAP_RET‐
              VALUE one can use THIS->foo and THIS->__retvalue respec‐
              tively inside the function. This is useful for quickly mi‐
              grating code written for SystemTap version 1.7 and earli‐

       /* pragma:suffix */
              Emit the file-level containing C code near the end of the
              resulting kernel module C source file.

       /* unmodified-fnargs */
              in an embedded-C function, means that the function argu‐
              ments are not modified inside the function body.

       /* string */
              in embedded-C expressions only, means that the expression
              has const char * type and should be treated as a string
              value, instead of the default long numeric.

       Script level global variables may be accessed in embedded-C func‐
       tions and blocks. To read or write the global variable var , the
       /* pragma:read:var */ or /* pragma:write:var */ marker must be
       first placed in the embedded-C function or block. This provides
       the macros STAP_GLOBAL_GET_* and STAP_GLOBAL_SET_* macros to al‐
       low reading and writing, respectively. For example:

              global var
              global var2[100]
              function increment() %{
                  /* pragma:read:var */ /* pragma:write:var */
                  /* pragma:read:var2 */ /* pragma:write:var2 */
                  STAP_GLOBAL_SET_var(STAP_GLOBAL_GET_var()+1); //var++
                  STAP_GLOBAL_SET_var2(1, 1, STAP_GLOBAL_GET_var2(1, 1)+1); //var2[1,1]++

       Variables may be read and set in both embedded-C functions and
       expressions.  Strings returned from embedded-C code are decayed
       to pointers. Variables must also be assigned at script level to
       allow for type inference. Map assignment does not return the val‐
       ue written, so chaining does not work.

       A set of builtin probe point aliases are provided by the scripts
       installed in the directory specified in the stappaths(7) manual
       page.  The functions are described in the stapprobes(3stap) manu‐
       al page.

       Integers can be dereferenced from pointers saved as a script in‐
       teger variables using the @kderef() or @uderef() operators.
       @kderef() is used for kernel space addresses and @uderef() is
       used for user space addresses.

              @kderef(SIZE, addr)
              @uderef(SIZE, addr)

       This will interpret addr as a kernel/user address and read SIZE
       bytes starting at that address.  SIZE should be either 1, 2, 4 or
       8 bytes.

       The value stored within a register can be accessed using the
       @kregister() or @uregister() operators.  @kregister() is used for
       kernel space registers and @uregister() is used for user space
       registers. The register of interest is specified using its DWARF


PROCESSING         top

       The translator begins pass 1 by parsing the given input script,
       and all scripts (files named *.stp) found in a tapset directory.
       The directories listed with -I are processed in sequence, each
       processed in "guru mode".  For each directory, a number of
       subdirectories are also searched.  These subdirectories are
       derived from the selected kernel version (the -R option), in
       order to allow more kernel-version-specific scripts to override
       less specific ones.  For example, for a kernel version
       2.6.12-23.FC3 the following patterns would be searched, in
       sequence: 2.6.12-23.FC3/*.stp, 2.6.12/*.stp, 2.6/*.stp, and
       finally *.stp.  Stopping the translator after pass 1 causes it to
       print the parse trees.

       In pass 2, the translator analyzes the input script to resolve
       symbols and types.  References to variables, functions, and probe
       aliases that are unresolved internally are satisfied by searching
       through the parsed tapset script files.  If any tapset script
       file is selected because it defines an unresolved symbol, then
       the entirety of that file is added to the translator's resolution
       queue.  This process iterates until all symbols are resolved and
       a subset of tapset script files is selected.

       Next, all probe point descriptions are validated against the wide
       variety supported by the translator.  Probe points that refer to
       code locations ("synchronous probe points") require the
       appropriate kernel debugging information to be installed.  In the
       associated probe handlers, target-side variables (whose names
       begin with "$") are found and have their run-time locations

       Next, all probes and functions are analyzed for optimization
       opportunities, in order to remove variables, expressions, and
       functions that have no useful value and no side-effect.
       Embedded-C functions are assumed to have side-effects unless they
       include the magic string /* pure */.  Since this optimization can
       hide latent code errors such as type mismatches or invalid
       $context variables, it sometimes may be useful to disable the
       optimizations with the -u option.

       Finally, all variable, function, parameter, array, and index
       types are inferred from context (literals and operators).
       Stopping the translator after pass 2 causes it to list all the
       probes, functions, and variables, along with all inferred types.
       Any inconsistent or unresolved types cause an error.

       In pass 3, the translator writes C code that represents the
       actions of all selected script files, and creates a Makefile to
       build that into a kernel object.  These files are placed into a
       temporary directory.  Stopping the translator at this point
       causes it to print the contents of the C file.

       In pass 4, the translator invokes the Linux kernel build system
       to create the actual kernel object file.  This involves running
       make in the temporary directory, and requires a kernel module
       build system (headers, config and Makefiles) to be installed in
       the usual spot /lib/modules/VERSION/build.  Stopping the
       translator after pass 4 is the last chance before running the
       kernel object.  This may be useful if you want to archive the

       In pass 5, the translator invokes the systemtap auxiliary program
       staprun program for the given kernel object.  This program
       arranges to load the module then communicates with it, copying
       trace data from the kernel into temporary files, until the user
       sends an interrupt signal.  Any run-time error encountered by the
       probe handlers, such as running out of memory, division by zero,
       exceeding nesting or runtime limits, results in a soft error
       indication.  Soft errors in excess of MAXERRORS block of all
       subsequent probes (except error-handling probes), and terminate
       the session.  Finally, staprun unloads the module, and cleans up.

       One should avoid killing the stap process forcibly, for example
       with SIGKILL, because the stapio process (a child process of the
       stap process) and the loaded module may be left running on the
       system.  If this happens, send SIGTERM or SIGINT to any remaining
       stapio processes, then use rmmod to unload the systemtap module.

EXAMPLES         top

       See the stapex(3stap) manual page for a brief collection of
       samples, or a large set of installed samples under the systemtap
       documentation/testsuite directories.  See stappaths(7stap) for
       the likely location of these on the system.

CACHING         top

       The systemtap translator caches the pass 3 output (the generated
       C code) and the pass 4 output (the compiled kernel module) if
       pass 4 completes successfully.  This cached output is reused if
       the same script is translated again assuming the same conditions
       exist (same kernel version, same systemtap version, etc.).
       Cached files are stored in the $SYSTEMTAP_DIR/cache directory.
       The cache can be limited by having the file cache_mb_limit placed
       in the cache directory (shown above) containing only an ASCII
       integer representing how many MiB the cache should not exceed. In
       the absence of this file, a default will be created with the
       limit set to 256MiB.  This is a 'soft' limit in that the cache
       will be cleaned after a new entry is added if the cache clean
       interval is exceeded, so the total cache size may temporarily
       exceed this limit. This interval can be specified by having the
       file cache_clean_interval_s placed in the cache directory (shown
       above) containing only an ASCII integer representing the interval
       in seconds. In the absence of this file, a default will be
       created with the interval set to 300 s.


       Systemtap may be used as a powerful administrative tool.  It can
       expose kernel internal data structures and potentially private
       user information.  (In dyninst runtime mode, this is not the
       case, see the ALTERNATE RUNTIMES section below.)

       The translator asserts many safety constraints during compilation
       and more during run-time.  It aims to ensure that no handler
       routine can run for very long, allocate boundless memory, perform
       unsafe operations, or in unintentionally interfere with the
       system.  Uses of script global variables are automatically
       read/write locked as appropriate, to protect against manipulation
       by concurrent probe handlers.  Locks are taken so as to run the
       global-variable manipulation portion of probe handlers atomically
       (locks are taken all-or-none).  Deadlocks are detected with
       timeouts.  Use the -t flag to receive reports of excessive lock
       contention.  Experimenting with scripts is therefore generally
       safe.  The guru-mode -g option allows administrators to bypass
       most safety measures, which permits invasive or state-changing
       operations, embedded-C code, and increases the risk of upset.  By
       default, overload prevention is turned on for all modules.  If
       you would like to disable overload processing, use the
       --suppress-time-limits option.

       Errors that are caught at run time normally result in a clean
       script shutdown and a pass-5 error message.  The
       --suppress-handler-errors option lets scripts tolerate soft
       errors without shutting down.

       For the normal linux-kernel-module runtime, to run the kernel
       objects systemtap builds, a user must be one of the following:

       •   the root user;

       •   a member of the stapdev and stapusr groups;

       •   a member of the stapsys and stapusr groups; or

       •   a member of the stapusr group.

       The root user or a user who is a member of both the stapdev and
       stapusr groups can build and run any systemtap script.

       A user who is a member of both the stapsys and stapusr groups can
       only use pre-built modules under the following conditions:

       •   The module has been signed by a trusted signer. Trusted
           signers are normally systemtap compile-servers which sign
           modules when the --privilege option is specified by the
           client. See the stap-server(8) manual page for more

       •   The module was built using the --privilege=stapsys or the
           --privilege=stapusr options.

       Members of only the stapusr group can only use pre-built modules
       under the following conditions:

       •   The module is located in the /lib/modules/VERSION/systemtap
           directory.  This directory must be owned by root and not be
           world writable.


       •   The module has been signed by a trusted signer. Trusted
           signers are normally systemtap compile-servers which sign
           modules when the --privilege option is specified by the
           client. See the stap-server(8) manual page for more

       •   The module was built using the --privilege=stapusr option.

       The kernel modules generated by stap program are run by the
       staprun program.  The latter is a part of the Systemtap package,
       dedicated to module loading and unloading (but only in the white
       zone), and kernel-to-user data transfer.  Since staprun does not
       perform any additional security checks on the kernel objects it
       is given, it would be unwise for a system administrator to add
       untrusted users to the stapdev or stapusr groups.

       If the current system has SecureBoot turned on in the UEFI
       firmware, all kernel modules must be signed.  (Some kernels may
       allow disabling SecureBoot long after booting with a key sequence
       such as SysRq-X, making it unnecessary to sign modules.)  There
       are two ways to sign a systemtap module.  The systemtap compile
       server can sign modules with a MOK (Machine Owner Key) that it
       has in common with a client system.  For example:

              stap --use-server=HOSTNAME:PORT -e 'SCRIPT'
              # If there is no mok key in common with the server's systemtap mok key
              # list and the client's mok database then the user is directed by stap
              # to invoke:
              sudo mokutil --import signing_key.x509
              # then after rebooting the system:
              stap --use-server=HOSTNAME:PORT -e 'SCRIPT'
              # will use the server to build and sign the module and the module will run
              # on the client

       Another way to sign modules is to use the stap --sign-module op‐
       tion, which uses a MOK on the client system without using a serv‐
       er.  For example:

              stap --sign-module -e 'SCRIPT'
              # If there is no systemtap mok key in the system mok database
              # then the user is directed by stap to invoke:
              sudo mokutil --import /home/USER/.systemtap/ssl/server/moks/FINGERPRINT/signing_key.x509
              # then after rebooting the system:
              stap --sign-module -e 'SCRIPT'
              # will sign and run the module

       See the following wiki page for more details:


       Some kernels do not let systemtap guess whether module module
       signing is in effect.  On such machines, set the SYSTEMTAP_SIGN
       environment variable to any value while running stap.

       Many resource use limits are set by macros in the generated C
       code.  These may be overridden with -D flags.  A selection of
       these is as follows:

              Maximum number of nested function calls.  Default deter‐
              mined by script analysis, with a bonus 10 slots added for
              recursive scripts.

              Maximum length of strings, default 128.

              Maximum number of iterations to wait for locks on global
              variables before declaring possible deadlock and skipping
              the probe, default 1000.

              Maximum number of statements to execute during any single
              probe hit (with interrupts disabled), default 1000.  Note
              that for straight-through probe handlers lacking loops or
              recursion, due to optimization, this parameter may be in‐
              terpreted too conservatively.

              Maximum number of statements to execute during any single
              probe hit which is executed with interrupts enabled (such
              as begin/end probes), default (MAXACTION * 10).

              Maximum number of stack frames that will be be processed
              by the stap runtime unwinder as produced by the backtrace
              functions in the [u]context-unwind.stp tapsets, default

              Maximum number of rows in any single global array, default
              2048.  Individual arrays may be declared with a larger or
              smaller limit instead:

              global big[10000],little[5]

              or denoted with % to make them wrap-around (replace old
              entries) automatically, as in

              global big%

              or both.

              The number of powers-of-two to add or subtract from the
              natural size of the hash table backing each global asso‐
              ciative array.  Default is 0.  Try small positive numbers
              to get extra performance at the cost of more memory con‐
              sumption, because that should reduce hash table colli‐
              sions.  Try small negative numbers for the opposite trade‐

              Maximum number of soft errors before an exit is triggered,
              default 0, which means that the first error will exit the
              script.  Note that with the --suppress-handler-errors op‐
              tion, this limit is not enforced.

              Maximum number of skipped probes before an exit is trig‐
              gered, default 100.  Running systemtap with -t (timing)
              mode gives more details about skipped probes.  With the
              default -DINTERRUPTIBLE=1 setting, probes skipped due to
              reentrancy are not accumulated against this limit.  Note
              that with the --suppress-handler-errors option, this limit
              is not enforced.

              Minimum number of free kernel stack bytes required in or‐
              der to run a probe handler, default 1024.  This number
              should be large enough for the probe handler's own needs,
              plus a safety margin.

              Maximum number of concurrently armed user-space probes
              (uprobes), default somewhat larger than the number of
              user-space probe points named in the script.  This pool
              needs to be potentially large because individual uprobe
              objects (about 64 bytes each) are allocated for each
              process for each matching script-level probe.

              Maximum amount of memory (in kilobytes) that the systemtap
              module should use, default unlimited.  The memory size in‐
              cludes the size of the module itself, plus any additional
              allocations.  This only tracks direct allocations by the
              systemtap runtime.  This does not track indirect alloca‐
              tions (as done by kprobes/uprobes/etc. internals).

              Maximum number of machine cycles spent in probes on any
              cpu per given interval, before an overload condition is
              declared and the script shut down.  The defaults are 500
              million and 1 billion, so as to limit stap script cpu con‐
              sumption at around 50%.

              Size of procfs probe read buffers (in bytes).  Defaults to
              MAXSTRINGLEN.  This value can be overridden on a per-
              procfs file basis using the procfs read probe .max‐
              size(MAXSIZE) parameter.

       With scripts that contain probes on any interrupt path, it is
       possible that those interrupts may occur in the middle of another
       probe handler.  The probe in the interrupt handler would be
       skipped in this case to avoid reentrance.  To work around this
       issue, execute stap with the option -DINTERRUPTIBLE=0 to mask in‐
       terrupts throughout the probe handler.  This does add some extra
       overhead to the probes, but it may prevent reentrance for common
       problem cases.  However, probes in NMI handlers and in the call‐
       path of the stap runtime may still be skipped due to reentrance.

       In case something goes wrong with stap or staprun after a probe
       has already started running, one may safely kill both user
       processes, and remove the active probe kernel module with rmmod.
       Any pending trace messages may be lost.


       Systemtap exposes kernel internal data structures and potentially
       private user information. Because of this, use of systemtap's
       full capabilities are restricted to root and to users who are
       members of the groups stapdev and stapusr.

       However, a restricted set of systemtap's features can be made
       available to trusted, unprivileged users. These users are members
       of the group stapusr only, or members of the groups stapusr and
       stapsys.  These users can load systemtap modules which have been
       compiled and certified by a trusted systemtap compile-server. See
       the descriptions of the options --privilege and --use-server. See
       README.unprivileged in the systemtap source code for information
       about setting up a trusted compile server.

       The restrictions enforced when --privilege=stapsys is specified
       are designed to prevent unprivileged users from:

              •   harming the system maliciously.

       The restrictions enforced when --privilege=stapusr is specified
       are designed to prevent unprivileged users from:

              •   harming the system maliciously.

              •   gaining access to information which would not normally
                  be available to an unprivileged user.

              •   disrupting the performance of processes owned by other
                  users of the system.  Some overhead to the system in
                  general is unavoidable since the unprivileged  user's
                  probes will be triggered at the appropriate times.
                  What we would like to avoid is targeted interruption
                  of another user's processes which would not normally
                  be possible by an unprivileged user.

       A member of the groups stapusr and stapsys may use all probe

       A member of only the group stapusr may use only the following

              •   begin, begin(n)

              •   end, end(n)

              •   error(n)

              •   never

              •   process.*, where the target process is owned by the

              •   timer.{jiffies,s,sec,ms,msec,us,usec,ns,nsec}(n)*

              •   timer.hz(n)

       The following scripting language features are unavailable to all
       unprivileged users:

              •   any feature enabled by the Guru Mode (-g) option.

              •   embedded C code.

       The following runtime restrictions are placed upon all unprivi‐
       leged users:

              •   Only the default runtime code (see -R) may be used.

       Additional restrictions are placed on members of only the group

              •   Probing of processes owned by other users is not per‐

              •   Access of kernel memory (read and write) is not per‐

       Some command line options provide access to features which must
       not be available to all unprivileged users:

              •   -g may not be specified.

              •   The following options may not be used by the compile-
                  server client:

                      -a, -B, -D, -I, -r, -R

       The following environment variables must not be set for all un‐
       privileged users:


       In general, tapset functions are only available for members of
       the group stapusr when they do not gather information that an or‐
       dinary program running with that user's privileges would be de‐
       nied access to.

       There are two categories of unprivileged tapset functions. The
       first category consists of utility functions that are uncondi‐
       tionally available to all users; these include such things as:

              cpu:long ()
              exit ()
              str_replace:string (prnt_str:string, srch_str:string, rplc_str:string)

       The second category consists of so-called myproc-unprivileged
       functions that can only gather information within their own
       processes. Scripts that wish to use these functions must test the
       result of the tapset function is_myproc and only call these func‐
       tions if the result is 1. The script will exit immediately if any
       of these functions are called by an unprivileged user within a
       probe within a process which is not owned by that user. Examples
       of myproc-unprivileged functions include:

              print_usyms (stk:string)
              user_int:long (addr:long)
              usymname:string (addr:long)

       A compile error is triggered when any function not in either of
       the above categories is used by members of only the group sta‐

       No other built-in tapset functions may be used by members of only
       the group stapusr.


       As described above, systemtap's default runtime mode involves
       building and loading kernel modules, with various security trade‐
       offs presented.  Systemtap now includes two new prototype back‐
       ends: --runtime=dyninst and --runtime=bpf.

       --runtime=dyninst uses Dyninst to instrument a user's own
       processes at runtime. This backend does not use kernel modules,
       and does not require root privileges, but is restricted with re‐
       spect to the kinds of probes and other constructs that a script
       may use. dyninst runtime operates in target-attach mode, so it
       does require a -c COMMAND or -x PID process.  For example:

              stap --runtime=dyninst -c 'stap -V' \
                   -e 'probe process.function("main")
                       { println("hi from dyninst!") }'

       It may be necessary to disable a conflicting selinux check with

              # setsebool allow_execstack 1

       --runtime=bpf compiles the user script into extended Berkeley
       Packet Filter (eBPF) programs instead of a kernel module. eBPF
       programs are verified by the kernel for safety and are executed
       by an in-kernel virtual machine.  This runtime is in an early
       stage of development and currently lacks support for a number of
       features available in the default runtime. Please see the
       stapbpf(8) man page for more information.

EXIT STATUS         top

       The systemtap translator generally returns with a success code of
       0 if the requested script was processed and executed successfully
       through the requested pass.  Otherwise, errors may be printed to
       stderr and a failure code is returned.  Use -v or -vp N to in‐
       crease (global or per-pass) verbosity to identify the source of
       the trouble.

       In listings mode (-l and -L), error messages are normally sup‐
       pressed.  A success code of 0 is returned if at least one match‐
       ing probe was found.

       A script executing in pass 5 that is interrupted with ^C / SIGINT
       is considered to be successful.

DEPRECATION         top

       Over time, some features of the script language and the tapset
       library may undergo incompatible changes, so that a script writ‐
       ten against an old version of systemtap may no longer run.  In
       these cases, it may help to run systemtap with the --compatible
       VERSION flag, specifying the last known working version.  Running
       systemtap with the --check-version flag will output a warning if
       any possible incompatible elements have been parsed.  Deprecation
       historical details may be found in the NEWS file.

       The purpose of deprecation facility is to improve the experience
       of scripts written for newer versions of systemtap (by adding
       better alternatives and removing conflicting or messy older al‐
       ternatives), while at the same time permitting scripts written
       for older versions of systemtap to continue running.  Deprecation
       is thus intended a service to users (and an inconvenience to sys‐
       temtap's developers), rather than the other way around.

       Please note that underscore-prefixed identifiers in the tapset
       sometimes undergo such changes that are difficult to preserve
       compatibility for, even with the deprecation mechanisms.  Avoid
       relying on these in your scripts; instead propose them for promo‐
       tion to non-underscored status.

FILES         top

       Important files and their corresponding paths can be located in
              stappaths (7) manual page.

SEE ALSO         top


BUGS         top

       Use the Bugzilla link of the project web page or our mailing
       list. ,


COLOPHON         top

       This page is part of the systemtap (a tracing and live-system
       analysis tool) project.  Information about the project can be
       found at ⟨⟩.  If you have a bug
       report for this manual page, send it to
       This page was obtained from the project's upstream Git repository
       ⟨git://⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to


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