Quick tip: Create a CentOS 6 guest with EPEL packages

You can use virt-builder [≥ 1.26] to create guests with packages from other repositories, like this:

$ virt-builder centos-6 \
    --run-command 'rpm -ivh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm' \
    --update \
    --install cloud-utils,cloud-init

(cloud-utils & cloud-init are examples of packages that are only available in EPEL)

libguestfs on RHEL 5

I’ve spent the past couple of weeks [sic] getting a modern libguestfs into RHEL 5. RHEL 5 was first released in March 2007 and is thus over 5 years old.

It’s hard work.

Firstly RHEL 5 lacks virtio-serial, which is the mechanism used by the library to talk to the appliance. We used to use a TCP connection, but we gave that up since it’s slow, awkward and possibly insecure. To get RHEL 5 going again, I had to forward port the old TCP code into a modern branch of libguestfs.

Secondly RHEL 5 lacks a lot of features that libguestfs presents through the API. I got most of them working by carefully fixing and rewriting code, but some of them are impossible to do (eg. btrfs support).

Altogether I wrote about 30 patches, with about half going upstream, and the other half sitting in an “old Linux”-only side branch.

The release notes are attached below, and the packages should be available in EPEL 5 in a few days.

---

libguestfs for EPEL 5
by Richard W.M. Jones

This package contains modern libguestfs for EPEL 5. Although libguestfs is supplied in RHEL 5, the version supplied is very old and is only intended to be used with virt-v2v from RHEL 5. It is only available in the RHEL-5-V2V channel.

Therefore there exists a need for a modern libguestfs for RHEL 5 users. This package supplies this through the community-supported EPEL repository.

(1) Installation

After enabling the EPEL repository, install libguestfs in the normal way using yum. No post-installation configuration should be needed.

You must have a non-Xen kernel installed on the host. Note that the non-Xen kernel just needs to be installed, it does *not* need to be running (you can run libguestfs under Xen if you want). The non-Xen kernel is used to boot the libguestfs appliance.

You must use this package together with the version of qemu-kvm from RHEL 5 (usually called kvm-83-NNN.el5). Alternate versions of qemu, KVM, using $LIBGUESTFS_QEMU or QEMU wrappers, will probably not work.

Hardware virtualization will greatly improve the performance of libguestfs, but it is not required. libguestfs cannot use hardware virtualization when run in a Xen domain (not even dom0). For more performance tips, read guestfs-performance(1).

(2) Getting help

This package is supported voluntarily by the EPEL community and by the upstream libguestfs maintainers.

It is not supported by Red Hat.

It cannot be used with the virt-v2v package from RHEL 5. If you need to use virt-v2v on RHEL 5, use the libguestfs package from the same RHN channel. However we would advise you to use RHEL 6 or later because that version of virt-v2v is substantially more powerful.

To get help with this package, contact the libguestfs maintainers. See http://libguestfs.org for links to the mailing list, IRC, and how to file bugs.

(3) Features not available

The following features are not compatible with RHEL 5 and have been removed completely:

• PHP bindings
• GObject, GObject introspection, anything that uses GObject Introspection such as the Javascript bindings
• Erlang bindings
• The btrfs filesystem.
• guestfs_fstrim
• guestfs_wipefs
• Various APIs that take UUIDs (eg. guestfs_mkswap_U)
• virtio-scsi
• Internationalization of any non-C programs.

(4) Features that may not work

The following features may not work in this version of libguestfs:

• LUKS (encrypted filesystems within guests)
• MD (RAID devices within guests)
• FUSE, guestmount, the mount-local API. These appear to have some problems because of the older version of FUSE in RHEL 5.
• virt-sysprep --script option (because it requires FUSE).
• The ntfsclone_* APIs only partially work. In particular, the metadataonly flag is not working, and maybe other parts of this API won’t work.
• guestfs_vfs_label cannot read labels from NTFS filesystems.
• guestfs_blkid may return fewer fields than expected on a more modern Linux system.
• guestfs_txz_in and guestfs_txz_out don’t work.
• guestfs_utimens doesn’t let you set the time on a symbolic link (this is a limitation of the RHEL 5 kernel).
• guestfs_mkswap_label followed by guestfs_swapon_label does not work. The reasons are not well understood.
• Adding drives using non-virtio-blk interfaces.

(5) Other notes

An artificial pause of 1 second has been added after unmounting any filesystem.

*Without* the 1 second pause, the following test case will fail sometimes:

  guestfish <<EOF
  sparse test1.img 1G
  run
  part-disk /dev/sda mbr
  mkfs msdos /dev/sda1
  mount /dev/sda1 /
  touch /foo
  umount /
  mkfs ntfs /dev/sda1
  # Next command would fail:
  mount /dev/sda1 /
  vfs-type /dev/sda1 -x
  EOF

With the 1 second pause, this case passes. The reason is not understood.

libguestfs versions

A useful table (original posting and explanation of version numbers):

Rawhide	1.5.x (currently 1.5.0)
Fedora 13	1.4.x (currently 1.4.1)
Fedora 12	1.2.x (currently 1.2.10)
EPEL 5	1.2.x (currently 1.2.10)
RHEL 6.0	1.2.7 + backported fixes and features needed for V2V
RHEL 6.1	undecided, probably rebase to latest 1.2.x or 1.4.x
RHEL 5.5 with RHEV-M subscription	1.2.7 + backported fixes and features needed for V2V