2.3. Running SystemTap Scripts
SystemTap scripts are run through the command stap
. stap
can run SystemTap scripts from standard input or from file.
Running stap
and staprun
requires elevated privileges to the system. However, not all users can be granted root access just to run SystemTap. In some cases, for instance, you may want to allow a non-privileged user to run SystemTap instrumentation on his machine.
To allow ordinary users to run SystemTap without root access, add them to one of these user groups:
- stapdev
Members of this group can use stap
to run SystemTap scripts, or staprun
to run SystemTap instrumentation modules.
Running stap
involves compiling SystemTap scripts into kernel modules and loading them into the kernel. This requires elevated privileges to the system, which are granted to stapdev
members. Unfortunately, such privileges also grant effective root access to stapdev
members. As such, you should only grant stapdev
group membership to users whom you can trust root access.
- stapusr
Members of this group can only run staprun
to run SystemTap instrumentation modules. In addition, they can only run those modules from /lib/modules/kernel_version
/systemtap/
. Note that this directory must be owned only by the root user, and must only be writable by the root user.
Below is a list of commonly used stap
options:
- -v
Makes the output of the SystemTap session more verbose. You can repeat this option (for example, stap -vvv script.stp
) to provide more details on the script's execution. This option is particularly useful if you encounter any errors in running the script.
- -o
filename
Sends the standard output to file (filename
).
- -x
process ID
Sets the SystemTap handler function
target()
to the specified process ID. For more information about
target()
, refer to
SystemTap Functions.
- -c
command
Sets the SystemTap handler function
target()
to the specified command. Note that you must use the full path to the specified command; for example, instead of specifying
cp
, use
/bin/cp
(as in
stap script
-c /bin/cp
). For more information about
target()
, refer to
SystemTap Functions.
- -e '
script
'
Use script
string rather than a file as input for systemtap translator.
You can also instruct stap
to run scripts from standard input using the switch -
. To illustrate:
echo "probe timer.s(1) {exit()}" | stap -
Example 2.1. Running Scripts From Standard Input
echo "probe timer.s(1) {exit()}" | stap -v -
For more information about stap
, refer to man stap
.
Note
The stap
options -v
and -o
also work for staprun
. For more information about staprun
, refer to man staprun
.