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 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.

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 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!

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 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
       to man-pages@man7.org

                                                                 STAPVIRT(1)