8 **qemu-storage-daemon** [options]
13 ``qemu-storage-daemon`` provides disk image functionality from QEMU,
14 ``qemu-img``, and ``qemu-nbd`` in a long-running process controlled via QMP
15 commands without running a virtual machine.
16 It can export disk images, run block job operations, and
17 perform other disk-related operations. The daemon is controlled via a QMP
18 monitor and initial configuration from the command-line.
20 The daemon offers the following subset of QEMU features:
31 Commands can be sent over a QEMU Monitor Protocol (QMP) connection. See the
32 :manpage:`qemu-storage-daemon-qmp-ref(7)` manual page for a description of the
35 The daemon runs until it is stopped using the ``quit`` QMP command or
36 SIGINT/SIGHUP/SIGTERM.
38 **Warning:** Never modify images in use by a running virtual machine or any
39 other process; this may destroy the image. Also, be aware that querying an
40 image that is being modified by another process may encounter inconsistent
46 .. program:: qemu-storage-daemon
50 .. option:: -h, --help
54 .. option:: -V, --version
56 Display version information and exit
58 .. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE]
60 .. include:: ../qemu-option-trace.rst.inc
62 .. option:: --blockdev BLOCKDEVDEF
64 is a block node definition. See the :manpage:`qemu(1)` manual page for a
65 description of block node properties and the :manpage:`qemu-block-drivers(7)`
66 manual page for a description of driver-specific parameters.
68 .. option:: --chardev CHARDEVDEF
70 is a character device definition. See the :manpage:`qemu(1)` manual page for
71 a description of character device properties. A common character device
72 definition configures a UNIX domain socket::
74 --chardev socket,id=char1,path=/var/run/qsd-qmp.sock,server=on,wait=off
76 .. option:: --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>][,writable=on|off][,bitmap=<name>]
77 --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=unix,addr.path=<socket-path>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
78 --export [type=]vhost-user-blk,id=<id>,node-name=<node-name>,addr.type=fd,addr.str=<fd>[,writable=on|off][,logical-block-size=<block-size>][,num-queues=<num-queues>]
79 --export [type=]fuse,id=<id>,node-name=<node-name>,mountpoint=<file>[,growable=on|off][,writable=on|off]
81 is a block export definition. ``node-name`` is the block node that should be
82 exported. ``writable`` determines whether or not the export allows write
83 requests for modifying data (the default is off).
85 The ``nbd`` export type requires ``--nbd-server`` (see below). ``name`` is
86 the NBD export name (if not specified, it defaults to the given
87 ``node-name``). ``bitmap`` is the name of a dirty bitmap reachable from the
88 block node, so the NBD client can use NBD_OPT_SET_META_CONTEXT with the
89 metadata context name "qemu:dirty-bitmap:BITMAP" to inspect the bitmap.
91 The ``vhost-user-blk`` export type takes a vhost-user socket address on which
92 it accept incoming connections. Both
93 ``addr.type=unix,addr.path=<socket-path>`` for UNIX domain sockets and
94 ``addr.type=fd,addr.str=<fd>`` for file descriptor passing are supported.
95 ``logical-block-size`` sets the logical block size in bytes (the default is
96 512). ``num-queues`` sets the number of virtqueues (the default is 1).
98 The ``fuse`` export type takes a mount point, which must be a regular file,
99 on which to export the given block node. That file will not be changed, it
100 will just appear to have the block node's content while the export is active
101 (very much like mounting a filesystem on a directory does not change what the
102 directory contains, it only shows a different content while the filesystem is
103 mounted). Consequently, applications that have opened the given file before
104 the export became active will continue to see its original content. If
105 ``growable`` is set, writes after the end of the exported file will grow the
108 .. option:: --monitor MONITORDEF
110 is a QMP monitor definition. See the :manpage:`qemu(1)` manual page for
111 a description of QMP monitor properties. A common QMP monitor definition
112 configures a monitor on character device ``char1``::
114 --monitor chardev=char1
116 .. option:: --nbd-server addr.type=inet,addr.host=<host>,addr.port=<port>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
117 --nbd-server addr.type=unix,addr.path=<path>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
118 --nbd-server addr.type=fd,addr.str=<fd>[,tls-creds=<id>][,tls-authz=<id>][,max-connections=<n>]
120 is a server for NBD exports. Both TCP and UNIX domain sockets are supported.
121 A listen socket can be provided via file descriptor passing (see Examples
122 below). TLS encryption can be configured using ``--object`` tls-creds-* and
123 authz-* secrets (see below).
125 To configure an NBD server on UNIX domain socket path
126 ``/var/run/qsd-nbd.sock``::
128 --nbd-server addr.type=unix,addr.path=/var/run/qsd-nbd.sock
130 .. option:: --object help
132 --object <type>[,<property>=<value>...]
134 is a QEMU user creatable object definition. List object types with ``help``.
135 List object properties with ``<type>,help``. See the :manpage:`qemu(1)`
136 manual page for a description of the object properties.
138 .. option:: --pidfile PATH
140 is the path to a file where the daemon writes its pid. This allows scripts to
141 stop the daemon by sending a signal::
143 $ kill -SIGTERM $(<path/to/qsd.pid)
145 A file lock is applied to the file so only one instance of the daemon can run
146 with a given pid file path. The daemon unlinks its pid file when terminating.
148 The pid file is written after chardevs, exports, and NBD servers have been
149 created but before accepting connections. The daemon has started successfully
150 when the pid file is written and clients may begin connecting.
154 Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute
157 $ qemu-storage-daemon \
158 --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \
159 --monitor chardev=char1
161 Launch the daemon from Python with a QMP monitor socket using file descriptor
162 passing so there is no need to busy wait for the QMP monitor to become
165 #!/usr/bin/env python3
169 sock_path = '/var/run/qmp.sock'
171 with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock:
172 listen_sock.bind(sock_path)
175 fd = listen_sock.fileno()
178 ['qemu-storage-daemon',
179 '--chardev', f'socket,fd={fd},server=on,id=char1',
180 '--monitor', 'chardev=char1'],
184 # listen_sock was automatically closed when leaving the 'with' statement
185 # body. If the daemon process terminated early then the following connect()
186 # will fail with "Connection refused" because no process has the listen
187 # socket open anymore. Launch errors can be detected this way.
189 qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
190 qmp_sock.connect(sock_path)
191 ...QMP interaction...
193 The same socket spawning approach also works with the ``--nbd-server
194 addr.type=fd,addr.str=<fd>`` and ``--export
195 type=vhost-user-blk,addr.type=fd,addr.str=<fd>`` options.
197 Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``::
199 $ qemu-storage-daemon \
200 --blockdev driver=file,node-name=disk,filename=disk.img \
201 --nbd-server addr.type=unix,addr.path=nbd.sock \
202 --export type=nbd,id=export,node-name=disk,writable=on
204 Export a qcow2 image file ``disk.qcow2`` as a vhost-user-blk device over UNIX
205 domain socket ``vhost-user-blk.sock``::
207 $ qemu-storage-daemon \
208 --blockdev driver=file,node-name=file,filename=disk.qcow2 \
209 --blockdev driver=qcow2,node-name=qcow2,file=file \
210 --export type=vhost-user-blk,id=export,addr.type=unix,addr.path=vhost-user-blk.sock,node-name=qcow2
212 Export a qcow2 image file ``disk.qcow2`` via FUSE on itself, so the disk image
213 file will then appear as a raw image::
215 $ qemu-storage-daemon \
216 --blockdev driver=file,node-name=file,filename=disk.qcow2 \
217 --blockdev driver=qcow2,node-name=qcow2,file=file \
218 --export type=fuse,id=export,node-name=qcow2,mountpoint=disk.qcow2,writable=on
223 :manpage:`qemu(1)`, :manpage:`qemu-block-drivers(7)`, :manpage:`qemu-storage-daemon-qmp-ref(7)`