37 Running virtual machines with qemu-system-ARCH #

Instead of entering the devices configuration options on the command line each time you want to run VM Guest, qemu-system-ARCH can read it from a file that was either previously saved with -writeconfig or edited manually.

Dumps the current virtual machine's devices configuration to a text file. It can be consequently re-used with the -readconfig option.

> sudo qemu-system-x86_64 -name "SLES 15 SP6" \
 -machine accel=kvm -M pc-i440fx-2.7 -m 512 -cpu kvm64 \
 -smp 2 /images/sles.raw -writeconfig /images/sles.cfg
(exited)
> cat /images/sles.cfg
# qemu config file

[drive]
  index = "0"
  media = "disk"
  file = "/images/sles_base.raw"

This way you can effectively manage the configuration of your virtual machines' devices in a well-arranged way.

Specifies the way the RTC is handled inside a VM Guest. By default, the clock of the guest is derived from that of the host system. Therefore, it is recommended that the host system clock is synchronized with an accurate external clock, for example, via NTP service.

If you need to isolate the VM Guest clock from the host one, specify clock=vm instead of the default clock=host.

You can also specify the initial time of the VM Guest's clock with the base option:

> sudo qemu-system-x86_64 [...] -rtc clock=vm,base=2010-12-03T01:02:00

Instead of a time stamp, you can specify utc or localtime. The former instructs VM Guest to start at the current UTC value (Coordinated Universal Time, see https://en.wikipedia.org/wiki/UTC), while the latter applies the local time setting.

Specifies the path to the disk image that to be used with this drive. If not specified, an empty (removable) drive is assumed.

Specifies the type of interface to which the drive is connected. Currently only floppy, scsi, ide, or virtio are supported by SUSE. virtio defines a paravirtualized disk driver. Default is ide.

Specifies the index number of a connector on the disk interface (see the if option) where the drive is connected. If not specified, the index is automatically incremented.

Specifies the type of media. Can be disk for hard disks, or cdrom for removable CD-ROM drives.

Specifies the format of the connected disk image. If not specified, the format is autodetected. Currently, SUSE supports raw and qcow2 formats.

Specifies the caching method for the drive. Possible values are unsafe, writethrough, writeback, directsync, or none. To improve performance when using the qcow2 image format, select writeback. none disables the host page cache and, therefore, is the safest option. Default for image files is writeback. For more information, see Chapter 19, Disk cache modes.

Creates an empty device that outputs no data and drops any data it receives.

Connects to QEMU's process standard input and standard output.

Creates a two-way stream socket. If PATH is specified, a Unix socket is created:

> sudo qemu-system-x86_64 [...] -chardev \
socket,id=unix_socket1,path=/tmp/unix_socket1,server

The SERVER suboption specifies that the socket is a listening socket.

If PORT is specified, a TCP socket is created:

> sudo qemu-system-x86_64 [...] -chardev \
socket,id=tcp_socket1,host=localhost,port=7777,server,nowait

The command creates a local listening (server) TCP socket on port 7777. QEMU does not block waiting for a client to connect to the listening port (nowait).

Sends all network traffic from VM Guest to a remote host over the UDP protocol.

> sudo qemu-system-x86_64 [...] \
-chardev udp,id=udp_fwd,host=mercury.example.com,port=7777

The command binds port 7777 on the remote host mercury.example.com and sends VM Guest network traffic there.

Creates a new QEMU text console. You can optionally specify the dimensions of the virtual console:

> sudo qemu-system-x86_64 [...] -chardev vc,id=vc1,width=640,height=480 \
-mon chardev=vc1

The command creates a new virtual console called vc1 of the specified size, and connects the QEMU monitor to it.

Logs all traffic from VM Guest to a file on VM Host Server. The path is required and is automatically created if it does not exist.

> sudo qemu-system-x86_64 [...] \
-chardev file,id=qemu_log1,path=/var/log/qemu/guest1.log

Redirects the VM Guest's virtual serial port to a character device CHAR_DEV on VM Host Server. By default, it is a virtual console (vc) in graphical mode, and stdio in non-graphical mode. The -serial understands many sub-options. See the man page man 1 qemu for a complete list of them.

You can emulate up to four serial ports. Use -serial none to disable all serial ports.

Redirects the VM Guest's parallel port to a DEVICE. This option supports the same devices as -serial.

Tip

With SUSE Linux Enterprise Server as a VM Host Server, you can directly use the hardware parallel port devices /dev/parportN where N is the number of the port.

You can emulate up to three parallel ports. Use -parallel none to disable all parallel ports.

Redirects the QEMU monitor to a character device CHAR_DEV on VM Host Server. This option supports the same devices as -serial. By default, it is a virtual console (vc) in a graphical mode, and stdio in non-graphical mode.