anaconda will not create a new PReP boot partition on the root disk when performing a new Red Hat Enterprise Linux 6 installation on a system that contains existing PReP Boot partitions that need to be preserved. Consequently, the Power SMS boot manager will be unable to boot the new Red Hat Enterprise Linux 6 installation. To work around this issue,

Anaconda now utilizes NetworkManager for network interface configuration. Consequently, kickstart users that referenced the network settings located in /tmp/netinfo must now source the ifcfg files found in /etc/sysconfig/network-scripts

In some circumstances, disks that contain a whole disk format (e.g. a LVM Physical Volume populating a whole disk) are not cleared correctly using the clearpart --initlabel kickstart command. Adding the --all switch - as in clearpart --initlabel --all - ensures disks are cleared correctly.

The nodmraid boot parameter currently cannot be used to force installation on disks containing spurious BIOS RAID metadata. To work around this issue, boot into rescue mode and run the command dmraid -rE /dev/sdX on the disks in question. Alternatively, run dd if=/dev/zero of=/dev/sdX and let it process up until the end of the disk. Note, however that this alternate procedure may take longer to complete and will erase all data on the disk.

Installation of Red Hat Enterprise Linux 6 on an IBM ThinkPad T43 notebook may appear to stall after choosing storage options. In these circumstances, the installer is attempting to interact with the floppy drive, and may be unresponsive for up to 30 minutes.

During the installation on POWER systems, the error messages similar to:

attempt to access beyond end of deviceloop0: rw=0, want=248626, limit=248624

may be returned to sys.log. The errors do not prevent installation and only occur during initial setup. The filesystem created by the installer will function correctly.

Installation on large disks (i.e. more than 2TB) on non-EFI platforms may encounter some limitations. Many BIOS systems can only boot disks that contain MSDOS partition tables, which cannot fully address large disks. A GPT partition table can address the full disk, but may not be bootable from BIOS. Consequently, the Red Hat Enterprise Linux installer does not support installing the GRUB bootloader to disks that contain GPT partition tables on non-EFI systems. When installing Red Hat Enterprise Linux 6 on a non-EFI system that contains one or more large disks, create a GPT partition table on each of the disks before proceeding to the storage configuration portion of the install process. Leaving the large disks uninitialized, or using an MSDOS partition table on them, can cause problems when creating partitions using anaconda.

Some Cisco UCS storage devices do not have UEFI support, which may lead to an unbootable Red Hat Enterprise Linux 6 system when installation is performed through virtual media with the system in "strict UCSM boot order rules" mode. Consequently, when installing using the UEFI method, after installation and reboot, the system will hang with a flashing cursor. To work around this issue, install the system using the BIOS install method as follows: The use of BIOS install method will effectively work around the bug, but will prevent booting from disks using a GPT partition table. This will restrict the size of disks usable as a boot disk.

When installing on the s390x architecture, if the installation is being performed over SSH, avoid resizing the terminal window containing the SSH session. If the terminal window is resized during installation, the installer will exit and installation will terminate.

Multipath storage devices with serial numbers not exactly 16 or 32 characters in length will not be detected by anaconda during installation.

Due to an issue with the shutdown sequence of the installer, Intel BIOS RAID sets might be left in an unclean condition post installation. Consequently, they will be rebuilt during the first boot of the system after installation. Note that this issue has no impact other than a slower first boot up after installation.

The installer currently does not support having the /boot volume on a logical volume. Consequently, when setting up mount points during installation, the /boot volume cannot be on an LVM volume. System z supports /boot on an LVM volume. In order to exploit this, manual configuration after installation is required. Refer to the zipl documentation for further information.

Minimal installations lack NetworkManager, so users wishing to have network interfaces configured for use on the first boot after installation need to make sure the network interfaces are configured and the network service is enabled at boot time. The following kickstart commands will enable eth0 for DHCP and enable the 'network' service:

network --device eth0 --onboot yes --bootproto dhcpservices --enabled=network

Refer to the network device configuration documentation for more details on what the ifcfg-ethX files may contain.

The kernel image provided on the CD/DVD is too large for Open Firmware. Consequently, on the POWER architecture, directly booting the kernel image over a network from the CD/DVD is not possible. Instead, use yaboot to boot from a network.

The anaconda partition editing interface includes a button labeled Resize. Note that you can only shrink a partition with this button, not enlarge a partition.

System z installations cannot use the ext4 filesystem for the boot partition. The recommended alternative filesystem is ext3.

Channel IDs(read, write, data) for network devices are required for defining and configuring network devices on s390 systems. However, system-config-kickstart - the graphical user interface for generating a kickstart configuration - cannot define channel IDs for a network device. To work around this issue, manually edit the kickstart configuration that system-config-kickstart generates to include the desired network devices.

During an MPATH installation on IBM POWER 7 systems, a "DiskLabelCommit Error" might be returned. To work around this issue, first install the system in a single path configuration. Connect to the system via SSH, clear the partitions using the fdisk -l command, and delete the partitions, then exit the SSH session. Finally, continue the installation from the installer.

anaconda in Red Hat Enterprise Linux 6 for Power writes an incorrect value to /etc/rpm/macros that can cause issues when installing 32 and 64-bit PowerPC packages together. Users are advised to remove this file after installation.

When a system is configured to require smart card authentication, and there is no smartcard currently plugged into the system, then users might see the debug message:

ERROR: pam_pkcs11.c:334: no suitable token available'

This message can be safely ignored.

Red Hat Enterprise Linux 6 Beta features Dovecot version 2.0. The configuration files used by Dovecot 2.0 are significantly different from those found in dovecot 1.0.x, the version shipped in previous releases of Red Hat Enterprise Linux. Specifically, /etc/dovecot.conf has been split into /etc/dovecot/dovecot.conf and /etc/dovecot/conf.d/*.conf

Under some circumstances, the readahead service may cause the auditd service to stop. To work around this potential issue, disable the readahead collector by adding the following lines to the /etc/sysconfig/readahead configuration file:

READAHEAD_COLLECT="no"READAHEAD_COLLECT_ON_RPM="no"

Alternatively, the readahead package can be removed entirely.

An error exists in the communication process between the samba daemon and the Common Unix Printing System (CUPS) scheduler. Consequently, the first time a print job is submitted to a Red Hat Enterprise Linux 6 system via Server Message Block (SMB), a timeout will occur. To work around this issue, use the following command to create a CUPS certificate before the first print job is submitted:

lpstat -E -s

Under some circumstances, using the rhn_register command to register a system with the Red Hat Network (RHN) might fail. When this issue is encountered, the rhn_register command will return an error similar to:

# rhn_registerSegmentation fault (core dumped)or# rhn_register***MEMORY-ERROR***: rhn_register[11525]: GSlice: assertion failed:sinfo->n_allocated > 0Aborted (core dumped)

To work around this issue, set the following environment variable, then run the rhn_register command again:

G_SLICE=always-malloc

If a user has a .bashrc which outputs to stderr, the user will be unable to sftp into their account. From the user's point of view, the sftp session is immediately terminated after authentication.

Under some circumstances, installation of a Red Hat Enterprise Linux 6 virtual guest stalls after the optional testing of media. Note that this issue has only been observed with Red Hat Enterprise Linux 6 guests that utilize multiple virtualized CPUs. To work around this issue, use a media source that is known to be verified, and skip the media test, or use a single virtualized CPU during installation.

Cancelling the disk physical cache for block devices and use of barriers for filesystems may slow down qcow2 dramatically. Use the following command to reduce the frequency of sync requests by pre-allocating new images and setting the cluster size to 2M

./qemu-img create  -opreallocation=metadata -ocluster_size=2M -f qcow2 $DISK $SIZE

In earlier versions of Red Hat Enterprise Linux, libvirt permitted PCI devices to be insecurely assigned to guests. In Red Hat Enterprise Linux 6, assignment of insecure devices is disabled by default by libvirt. However, this may cause assignment of previously working devices to start failing. To enable the old, insecure setting, edit /etc/libvirt/qemu.conf, set "relaxed_acs_check = 1", and restart libvirtd. Note that this action will re-open possible security issues.

Users upgrading from pre-release versions of Red Hat Enterprise Linux 6 (i.e. the virt-v2v versions less than virt-v2v-0.6.2-2.el6) may be required to update the default virt-v2v configuration file. Specifically, the 'viostor' app for Windows guests is replaced by the 'virtio' app, which now points to the directory containing the complete driver. Refer to the updated default configuration file for further details.

I/O Advanced Programmable Interrupt Controller (I/O APIC) timer interrupts are not emulated as non-maskable interrupts (NMIs) to virtualized guests. Consequently, if a virtualized guest uses the kernel parameter nmi_watchdog=1, the guest kernel will panic on boot.

The balloon service on Windows 7 guests can only be started by the "Administrator" user.

Direct Asynchronous IO (AIO) that is not issued on filesystem block boundaries, and falls into a hole in a sparse file on ext4 or xfs filesystems, may corrupt file data if multiple I/O operations modify the same filesystem block. Specifically, if qemu-kvm is used with the aio=native IO mode over a sparse device image hosted on the ext4 or xfs filesystem, guest filesystem corruption will occur if partitions are not aligned with the host filesystem block size. Generally, do not use aio=native option along with cache=none for QEMU. This issue can be avoided by using one of the following techniques:

On Red Hat Enterprise Linux 6 KVM virtual guests, unmounting a filesystem on an mdraid volume does not immediately free the underlying device for the mdadm --stop operation. Consequently, during installation on a system with pre-existing mdraid volumes the following error can appear while anaconda is looking for storage devices:

MDRaidError: mddeactivate failed for /dev/md1: 08:26:59,485 ERROR   : Perhaps arunning process, mounted filesystem or active volume group?

To work around this issue, erase all data on the volume before installation by clearing the first several sectors of the volume with zeros.

Libvirt uses transient iptables rules for managing NAT or bridging to virtual machine guests. Any external command that reloads iptables state ( such as running system-config-firewall) will overwrite the entries needed by libvirt. Consequently, after running any command or tool that changes the state of iptables, guests may lose access the network. To work around this issue, use the command 'service libvirt reload' to restore libvirt's additional iptables rules.

Adding an rtl8139 NIC to an active Windows 2008 guest may result in the qemu-kvm process exiting. To work around this issue, shutdown the guest before adding additional rtl8139 NICs. Alternatively, install the virtio-net drivers and add a virtio NIC.

KVM users with a mix of virtio and ata disks should verify the boot device that anaconda chooses during installation. To verify the boot device, locate the "Install Target Devices" list in the disk selection screen that follows the partitioning type screen. Verify the boot device selection, which is indicated by a selector in the left-most column of the "Install Target Devices" list.

When installing Red Hat Enterprise Linux 6 as a new KVM guest, installer may incorrectly report amount of free memory available. Consequently, installation may terminate or switch to the text user interface. To work around this issue, increase amount of RAM allocated for the guest to 128 MB more than specified for the architecture and installation method.

A Windows virtual machine must be restarted after the installation of the kernel windows driver framework. If the virtual machine is not restarted it may crash when a memory balloon operation is performed.

Under some circumstances, if an 82576 Network driver (igb) is reloaded with the max_vfs=8 parameter and an uncorrectable PCIe AER error is seen on its port, the operation will hang or crash the host system. This error has been encountered with two 82576 devices connected via an IDT PES12N3A PCI Express Switch (rev 0c) plugged into a Westmere-EP's 5520/5500/X58 I/O Hub PCI Express Root Port 3. Note that other 82576 devices and IDT switches have worked in other Westmere-based systems

If the error occurs, two workarounds have been found to enable the use of all eight virtual functions (VFs) for guest virtual machines(VMs):

A dual function, 82576 interface (codename: Kawela, PCI Vendor/Device ID: 8086:10c9) cannot have both physical functions (PF's) device-assigned to a Windows 2008 guest. Either physical function can be device assigned to a Windows 2008 guest (PCI function 0 or function 1), but not both.

virt-v2v is able to convert guests running on ESX server. A current limitation in virt-v2v means that if an ESX guest has a disk with a snapshot, the snapshot must be on the same datastore as the underlying disk storage. If the snapshot and underlying storage are on different datastores, virt-v2v will report a 404 error while trying to retrieve the storage.

Under some circumstances, the virtio queue will fill if an application on a guest repeatedly writes to a virtio-serial character device while the host is not processing the queue. Consequently, the guest will enter an infinite loop and appear to be hung. Once the host side of the character device is read from, the guest will return to normal functionality.

The qemu-kvm options to enable VMware device emulation are not functional or supported in Red Hat Enterprise Linux 6.

Avoid running guestfish (without the --ro option), virt-edit, virt-tar (in upload mode), virt-win-reg (in merge mode) or guestmount (without the --ro option) on live virtual machine disks. If any of these tools are used on live virtual machines, disk corruption might occur.