1================================== 2QEMU persistent reservation helper 3================================== 4 5Synopsis 6-------- 7 8**qemu-pr-helper** [*OPTION*] 9 10Description 11----------- 12 13Implements the persistent reservation helper for QEMU. 14 15SCSI persistent reservations allow restricting access to block devices 16to specific initiators in a shared storage setup. When implementing 17clustering of virtual machines, it is a common requirement for virtual 18machines to send persistent reservation SCSI commands. However, 19the operating system restricts sending these commands to unprivileged 20programs because incorrect usage can disrupt regular operation of the 21storage fabric. QEMU's SCSI passthrough devices ``scsi-block`` 22and ``scsi-generic`` support passing guest persistent reservation 23requests to a privileged external helper program. :program:`qemu-pr-helper` 24is that external helper; it creates a socket which QEMU can 25connect to to communicate with it. 26 27If you want to run VMs in a setup like this, this helper should be 28started as a system service, and you should read the QEMU manual 29section on "persistent reservation managers" to find out how to 30configure QEMU to connect to the socket created by 31:program:`qemu-pr-helper`. 32 33After connecting to the socket, :program:`qemu-pr-helper` can 34optionally drop root privileges, except for those capabilities that 35are needed for its operation. 36 37:program:`qemu-pr-helper` can also use the systemd socket activation 38protocol. In this case, the systemd socket unit should specify a 39Unix stream socket, like this:: 40 41 [Socket] 42 ListenStream=/var/run/qemu-pr-helper.sock 43 44Options 45------- 46 47.. program:: qemu-pr-helper 48 49.. option:: -d, --daemon 50 51 run in the background (and create a PID file) 52 53.. option:: -q, --quiet 54 55 decrease verbosity 56 57.. option:: -v, --verbose 58 59 increase verbosity 60 61.. option:: -f, --pidfile=PATH 62 63 PID file when running as a daemon. By default the PID file 64 is created in the system runtime state directory, for example 65 :file:`/var/run/qemu-pr-helper.pid`. 66 67.. option:: -k, --socket=PATH 68 69 path to the socket. By default the socket is created in 70 the system runtime state directory, for example 71 :file:`/var/run/qemu-pr-helper.sock`. 72 73.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE] 74 75 .. include:: ../qemu-option-trace.rst.inc 76 77.. option:: -u, --user=USER 78 79 user to drop privileges to 80 81.. option:: -g, --group=GROUP 82 83 group to drop privileges to 84 85.. option:: -h, --help 86 87 Display a help message and exit. 88 89.. option:: -V, --version 90 91 Display version information and exit. 92