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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | TUTORIAL | SEE ALSO | BUGS | COLOPHON |
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 '--remote' 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-remove com‐
mand. 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 indicates
to libvirt to connect to the default driver. See the page at
<http://libvirt.org/uri.html> for supported values.
-d PATH
Specify the directory in which UNIX sockets should be created
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 command
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
definition. If the domain is currently running, it must be
powered off before changes take effect.
query DOMAIN
Display the following information about the domain: its name,
its UUID, its state, the number of permanent SystemTap 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. Otherwise
libvirt might have defaulted to e.g. 'qemu:///session'.
Rather than typing the URI everytime, it might be easier to instead
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 in‐
formation:
$ 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 domain,
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 related to the domain in it‐
self.
If hotplugging were supported, we could stop here and run stap di‐
rectly (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 created:
$ 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-remove
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/ ,<systemtap@sourceware.org>.
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 systemtap@sourceware.org. This page was
obtained from the project's upstream Git repository
⟨git://sourceware.org/git/systemtap.git⟩ on 2017-07-05. 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
to man-pages@man7.org
STAPVIRT(1)
Pages that refer to this page: stap(1)