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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | TUTORIAL | SEE ALSO | BUGS | COLOPHON |
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STAPVIRT(1) General Commands Manual STAPVIRT(1)
stapvirt - prepare libvirt domains for systemtap probing
stapvirt [-c URI] [-d PATH] [-v] COMMAND ARGUMENTS
The stapvirt program can be used to add ports to domains managed
by libvirt (see <http://libvirt.org/>). These ports can then be
used by stap to run scripts inside the domains (see the '--re‐
mote' option in stap(1) for more information).
Ports are added to the definition of the domain using the port-
add command. These ports can later be removed using the port-re‐
move command. Note that there can only be as many simultaneous
stap sessions as there are ports.
Starting from libvirt v1.1.1 and QEMU v0.10.0, SystemTap ports
can be hotplugged and thus do not need to be added first using
the port-add command. However, you need to ensure that there is
a virtio-serial controller in place so that hotplugged ports can
be connected. If creating a domain using virt-install, you can do
this by adding this option:
$ virt-install [...] --controller=virtio-serial
If the domain has already been created, you can simply do port-
add followed immediately by port-remove, and then power off and
restart the domain. The port will be removed, but the controller
will remain.
The following options are supported. Any other option prints a
short help message.
-c URI Specify the libvirt driver URI to which to connect (e.g.
'qemu:///system'). The default value is NULL, which indi‐
cates to libvirt to connect to the default driver. See the
page at <http://libvirt.org/uri.html> for supported val‐
ues.
-d PATH
Specify the directory in which UNIX sockets should be cre‐
ated when SystemTap ports are added. The default directory
is '/var/lib/libvirt/qemu'.
-v Increase verbosity. This option may be repeated for more
verbosity.
The following commands are recognized by stapvirt. Any other com‐
mand prints a short help message.
help Display the help message.
list List available domains.
port-add DOMAIN
Add a permanent SystemTap port to the domain's definition.
If the domain is currently running, it must be powered off
before changes take effect.
port-list DOMAIN
List the UNIX socket paths of the permanent SystemTap
ports in the domain's definition.
port-remove DOMAIN
Remove a permanent SystemTap port from the domain's defin‐
ition. If the domain is currently running, it must be pow‐
ered off before changes take effect.
query DOMAIN
Display the following information about the domain: its
name, its UUID, its state, the number of permanent System‐
Tap ports installed, and whether hotplugging is supported.
This tutorial will help you get started with stapvirt. Let's
start by listing all the privileged domains on the machine with
the list command:
$ stapvirt -c 'qemu:///system' list
Available domains on URI 'qemu:///system':
ID State Type Name
2 running persistent TestVM
Note that we specified the libvirt URI using the -c switch. Oth‐
erwise libvirt might have defaulted to e.g. 'qemu:///session'.
Rather than typing the URI everytime, it might be easier to in‐
stead set the LIBVIRT_DEFAULT_URI environment variable and omit
the -c switch. Note that this is a libvirt functionality (see
<libvirt.org/uri.html> for more details).
The list command indicates that we have a running domain named
'TestVM' with ID 2. Let's use the query command to retrieve more
information:
$ stapvirt query TestVM # by name
$ stapvirt query 2 # by ID
Name: TestVM
UUID: 905951c0-fa4f-409b-079c-c91ddda27028
State: running
ID: 2
Type: persistent
Permanent Ports: 0
Hotplugging: not supported
The query command gives us some basic information about the do‐
main, such as its name, UUID, and state. More importantly, it
gives us two pieces of information: the number of permanent ports
installed, and whether hotplugging is supported. Technically,
hotplugging support depends on libvirt and qemu, and is not re‐
lated to the domain in itself.
If hotplugging were supported, we could stop here and run stap
directly (assuming we have a virtio-serial controller already in
place, see DESCRIPTION). Since in our case hotplugging is not
supported, we need to add SystemTap ports. To do this, we use the
port-add command:
$ stapvirt port-add TestVM
Added new port org.systemtap.stapsh.0
The domain must be powered off before changes take effect.
We can confirm that a port was added by running the query command
again:
$ stapvirt query TestVM
...
Permanent Ports: 1
Hotplugging: not supported
It now indicates that there is 1 permanent port. We can also use
the port-list command to know exactly where the port will be cre‐
ated:
$ stapvirt port-list TestVM
/var/lib/libvirt/qemu/TestVM.org.systemtap.stapsh.0.sock
After powering off and restarting the domain, we are now ready to
use the port with stap:
$ stap -e 'probe begin { printf("Hello from TestVM!\n"); exit() }' \
--remote=libvirt://TestVM
Hello from TestVM!
Finally, if we'd like to remove the port, we can use the port-re‐
move command:
$ stapvirt port-remove TestVM
Removed port org.systemtap.stapsh.0
The domain must be powered off before changes take effect.
And that's all there is to it!
stap(1),
virt-install(1)
Use the Bugzilla link of the project web page or our mailing
list.
http://sourceware.org/systemtap/ ,<[email protected]>.
This page is part of the systemtap (a tracing and live-system
analysis tool) project. Information about the project can be
found at ⟨https://sourceware.org/systemtap/⟩. If you have a bug
report for this manual page, send it to [email protected].
This page was obtained from the project's upstream Git repository
⟨git://sourceware.org/git/systemtap.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
[email protected]
STAPVIRT(1)
Pages that refer to this page: stap(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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