stapvirt(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | TUTORIAL | SEE ALSO | BUGS | COLOPHON

STAPVIRT(1)              General Commands Manual             STAPVIRT(1)

NAME         top

       stapvirt - prepare libvirt domains for systemtap probing

SYNOPSIS         top

       stapvirt [-c URI] [-d PATH] [-v] COMMAND ARGUMENTS

DESCRIPTION         top

       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 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.

OPTIONS         top

       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.

COMMANDS         top

       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.

TUTORIAL         top

       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
       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
       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 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
       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!

SEE ALSO         top

       stap(1),
       virt-install(1)

BUGS         top

       Use the Bugzilla link of the project web page or our mailing
       list.
       http://sourceware.org/systemtap/ ,<systemtap@sourceware.org>.

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 ⟨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 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-26.)  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
       man-pages@man7.org

                                                             STAPVIRT(1)

Pages that refer to this page: stap(1)