STAPEX(3stap)                                                  STAPEX(3stap)

NAME         top

       stapex - systemtap examples


       These examples give a feel for basic systemtap syntax and control

              global odds, evens

              probe begin {
                # "no" and "ne" are local integers
                for (i=0; i<10; i++) {
                  if (i % 2) odds [no++] = i
                  else evens [ne++] = i
                delete odds[2]
                delete evens[3]
                exit ()

              probe end {
                foreach (x+ in odds) {
                  printf ("odds[%d] = %d\n", x, odds[x])
                foreach (x in evens-) {
                  printf ("evens[%d] = %d\n", x, evens[x])

       This prints:

              odds[1] = 1
              odds[3] = 5
              odds[4] = 7
              odds[5] = 9
              evens[5] = 8
              evens[4] = 6
              evens[2] = 2
              evens[1] = 0

       Note that all variables types are inferred, and that all locals and
       globals are automatically initialized.

       This script prints the primes between 0 and 49.

              function isprime (x) {
                if (x < 2) return 0
                for (i=2; i<x; i++) {
                  if (x % i == 0) return 0
                  if (i * i > x) break
                return 1
              probe begin {
                for (i=0; i<50; i++)
                  if (isprime (i)) printf("%d\n", i)

       This script demonstrates recursive functions.

              function fibonacci(i) {
                if (i < 1) error ("bad number")
                if (i == 1) return 1
                if (i == 2) return 2
                return fibonacci (i-1) + fibonacci (i-2)
              probe begin {
                printf ("11th fibonacci number: %d\n", fibonacci (11))
                exit ()

       Any larger number may exceed the MAXACTION or MAXNESTING limits, and
       result in an error.

PROBING         top

       To trace entry and exit from a function, use a pair of probes:

              probe kernel.function("sys_mkdir") { println ("enter") }
              probe kernel.function("sys_mkdir").return { println ("exit") }

       To list the probeable functions in the kernel, use the listings mode.

              % stap -l 'kernel.function("*")'

       To list the probeable functions and local variables in the kernel,
       use another listings mode.

              % stap -L 'kernel.function("*")'

MORE EXAMPLES         top

       The directory to find more examples can be found in the stappaths (7)
       manual page, and online at 

SEE ALSO         top


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 2017-03-13.  If you dis‐
       cover 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