| Boot devices on s390x |
| ===================== |
| |
| Booting with bootindex parameter |
| -------------------------------- |
| |
| For classical mainframe guests (i.e. LPAR or z/VM installations), you always |
| have to explicitly specify the disk where you want to boot from (or "IPL" from, |
| in s390x-speak -- IPL means "Initial Program Load"). |
| |
| So for booting an s390x guest in QEMU, you should always mark the |
| device where you want to boot from with the ``bootindex`` property, for |
| example:: |
| |
| qemu-system-s390x -drive if=none,id=dr1,file=guest.qcow2 \ |
| -device virtio-blk,drive=dr1,bootindex=1 |
| |
| Multiple devices may have a bootindex. The lowest bootindex is assigned to the |
| device to IPL first. If the IPL fails for the first, the device with the second |
| lowest bootindex will be tried and so on until IPL is successful or there are no |
| remaining boot devices to try. |
| |
| For booting from a CD-ROM ISO image (which needs to include El-Torito boot |
| information in order to be bootable), it is recommended to specify a ``scsi-cd`` |
| device, for example like this:: |
| |
| qemu-system-s390x -blockdev file,node-name=c1,filename=... \ |
| -device virtio-scsi \ |
| -device scsi-cd,drive=c1,bootindex=1 |
| |
| Note that you really have to use the ``bootindex`` property to select the |
| boot device. The old-fashioned ``-boot order=...`` command of QEMU (and |
| also ``-boot once=...``) is not supported on s390x. |
| |
| |
| Booting without bootindex parameter |
| ----------------------------------- |
| |
| The QEMU guest firmware (the so-called s390-ccw bios) has also some rudimentary |
| support for scanning through the available block devices. So in case you did |
| not specify a boot device with the ``bootindex`` property, there is still a |
| chance that it finds a bootable device on its own and starts a guest operating |
| system from it. However, this scanning algorithm is still very rough and may |
| be incomplete, so that it might fail to detect a bootable device in many cases. |
| It is really recommended to always specify the boot device with the |
| ``bootindex`` property instead. |
| |
| This also means that you should avoid the classical short-cut commands like |
| ``-hda``, ``-cdrom`` or ``-drive if=virtio``, since it is not possible to |
| specify the ``bootindex`` with these commands. Note that the convenience |
| ``-cdrom`` option even does not give you a real (virtio-scsi) CD-ROM device on |
| s390x. Due to technical limitations in the QEMU code base, you will get a |
| virtio-blk device with this parameter instead, which might not be the right |
| device type for installing a Linux distribution via ISO image. It is |
| recommended to specify a CD-ROM device via ``-device scsi-cd`` (as mentioned |
| above) instead. |
| |
| |
| Selecting kernels with the ``loadparm`` property |
| ------------------------------------------------ |
| |
| The ``s390-ccw-virtio`` machine supports the so-called ``loadparm`` parameter |
| which can be used to select the kernel on the disk of the guest that the |
| s390-ccw bios should boot. When starting QEMU, it can be specified like this:: |
| |
| qemu-system-s390x -machine s390-ccw-virtio,loadparm=<string> |
| |
| The first way to use this parameter is to use the word ``PROMPT`` as the |
| ``<string>`` here. In that case the s390-ccw bios will show a list of |
| installed kernels on the disk of the guest and ask the user to enter a number |
| to chose which kernel should be booted -- similar to what can be achieved by |
| specifying the ``-boot menu=on`` option when starting QEMU. Note that the menu |
| list will only show the names of the installed kernels when using a DASD-like |
| disk image with 4k byte sectors. On normal SCSI-style disks with 512-byte |
| sectors, there is not enough space for the zipl loader on the disk to store |
| the kernel names, so you only get a list without names here. |
| |
| The second way to use this parameter is to use a number in the range from 0 |
| to 31. The numbers that can be used here correspond to the numbers that are |
| shown when using the ``PROMPT`` option, and the s390-ccw bios will then try |
| to automatically boot the kernel that is associated with the given number. |
| Note that ``0`` can be used to boot the default entry. |
| |
| |
| Booting from a network device |
| ----------------------------- |
| |
| The firmware that ships with QEMU includes a small TFTP network bootloader |
| for virtio-net-ccw devices. The ``bootindex`` property is especially |
| important for booting via the network. If you don't specify the ``bootindex`` |
| property here, the network bootloader won't be taken into consideration and |
| the network boot will fail. For a successful network boot, try something |
| like this:: |
| |
| qemu-system-s390x -netdev user,id=n1,tftp=...,bootfile=... \ |
| -device virtio-net-ccw,netdev=n1,bootindex=1 |
| |
| The network bootloader also has basic support for pxelinux.cfg-style |
| configuration files. See the `PXELINUX Configuration page |
| <https://wiki.syslinux.org/wiki/index.php?title=PXELINUX#Configuration>`__ |
| for details how to set up the configuration file on your TFTP server. |
| The supported configuration file entries are ``DEFAULT``, ``LABEL``, |
| ``KERNEL``, ``INITRD`` and ``APPEND`` (see the `Syslinux Config file syntax |
| <https://wiki.syslinux.org/wiki/index.php?title=Config>`__ for more |
| information). |
