qemu-pr-helper [OPTION]
Implements the persistent reservation helper for QEMU.
SCSI persistent reservations allow restricting access to block devices
to specific initiators in a shared storage setup. When implementing
clustering of virtual machines, it is a common requirement for virtual
machines to send persistent reservation SCSI commands. However,
the operating system restricts sending these commands to unprivileged
programs because incorrect usage can disrupt regular operation of the
storage fabric. QEMU's SCSI passthrough devices scsi-block
and scsi-generic
support passing guest persistent reservation
requests to a privileged external helper program. :program:`qemu-pr-helper`
is that external helper; it creates a listener socket which will
accept incoming connections for communication with QEMU.
If you want to run VMs in a setup like this, this helper should be started as a system service, and you should read the QEMU manual section on "persistent reservation managers" to find out how to configure QEMU to connect to the socket created by :program:`qemu-pr-helper`.
After connecting to the socket, :program:`qemu-pr-helper` can optionally drop root privileges, except for those capabilities that are needed for its operation.
:program:`qemu-pr-helper` can also use the systemd socket activation protocol. In this case, the systemd socket unit should specify a Unix stream socket, like this:
[Socket] ListenStream=/var/run/qemu-pr-helper.sock
.. program:: qemu-pr-helper
.. option:: -d, --daemon run in the background (and create a PID file)
.. option:: -q, --quiet decrease verbosity
.. option:: -v, --verbose increase verbosity
.. option:: -f, --pidfile=PATH PID file when running as a daemon. By default the PID file is created in the system runtime state directory, for example :file:`/var/run/qemu-pr-helper.pid`.
.. option:: -k, --socket=PATH path to the socket. By default the socket is created in the system runtime state directory, for example :file:`/var/run/qemu-pr-helper.sock`.
.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] .. include:: ../qemu-option-trace.rst.inc
.. option:: -u, --user=USER user to drop privileges to
.. option:: -g, --group=GROUP group to drop privileges to
.. option:: -h, --help Display a help message and exit.
.. option:: -V, --version Display version information and exit.