The following issue applies to IBM Power Systems only.

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 device
loop0: 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 dhcp
services --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_register
Segmentation fault (core dumped)
or
# rhn_register
***MEMORY-ERROR***: rhn_register[11525]: GSlice: assertion failed:
sinfo->n_allocated > 0
Aborted (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 a
running 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.

Enterprise-class storage should always be mounted with using the -o nobarrier option.

When an LVM mirror suffers a device failure, a two-stage recovery takes place. The first stage involves removing the failed devices. This can result in the mirror being reduced to a linear device. The second stage — if configured to do so by the administrator — is to attempt to replace any of the failed devices. Note, however, that there is no guarantee that the second stage will choose devices previously in-use by the mirror that had not been part of the failure if others are available.

In Red Hat Enterprise Linux 5, infiniband support (specifically the openib start script and the openib.conf file) were supplied by the openib package. In Red Hat Enterprise Linux 6, the openib package is renamed to rdma. Additionally, the service has been renamed to rdma and the configuration file is now located in /etc/rdma/rdma.conf.

The NFSv4 server in Red Hat Enterprise Linux 6 currently allows clients to mount using UDP and advertises NFSv4 over UDP with rpcbind. However, this configuration is not supported by Red Hat and violates the RFC 3530 standard.

If a device-mapper-multipath device is still open, but all of the attached paths have been lost, the device is unable to create a new table with no paths. Consequently, the following unusual output may be returned from the multipath -ll output command:

mpatha (3600a59a0000c2fd0003079284c122fec) dm-0,
size=2.0G hwhandler='0'
|-+- policy='round-robin 0' prio=0 status=enabled
| `- #:#:#:# -   #:#  failed faulty running
`-+- policy='round-robin 0' prio=0 status=enabled
  |- #:#:#:# -   #:#  failed faulty running
  `- #:#:#:# -   #:#  failed faulty running

Output of this type indicates that there are no paths to the device. The erroneous lines in the output preceded by the string #:#:#:# will be removed in a future release.

ext2 and ext3 filesystems do not use a page_mkwrite mechanism to intercept page faults. The quota subsystem can not account for this additional usage when writing to disk. Consequently, a user may exceed their disk block quota by issuing memory-mapped writes into a sparse region of a file. Note, also, that this is a longstanding behavior in the ext2 and ext3 filesystems.

Parted in Red Hat Enterprise Linux 6 cannot handle Extended Address Volumes (EAV) Direct Access Storage Devices (DASD) that have greater than 65535 cylinders. Consequently, EAV DASD drives cannot be partitioned using parted and installation on EAV DASD drives will fail. To work around this issue, complete the installation on a non EAV DASD drive, then add the EAV device after installation using the tools provided in s390-utils.

Systems that have an Emulex FC controller (with SLI-3 based firmware) installed may return a kernel panic during install. If the SAN disk is not required for installation, work around this issue by disconnecting the SAN connection from the Emulex FC controller. Note that this issue does not occur on SLI-4 based controllers. To determine the firmware interface of the adapter, run the command

cat /sys/class/scsi_host/host{n}/fwrev

When multipath is configured to use user_friendly_names, it stores the binding between the wwid and the alias in /etc/multipath/bindings. When multipath creates devices in early bootup, (for example when the root filesystem is on a multipath device) it looks at /etc/multipath/bindings in the initramfs. When it creates devices during normal operation, it looks at /etc/multipath/bindings in the root filesystem. Currently, these two files aren't synced during initramfs creation. Because of this, there may be naming conflicts which keep new multipath devices from being created after bootup. To work around this, the bindings for the devices created by the initramfs must be copied into /etc/multipath/bindings after installation. The format of the bindings is:

<alias><space><wwid>

for example:

mpatha 3600d0230000000000e13955cc3757801

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:

Mixing the iSCSI discoveryd mode and the normal discovery mode is not supported. When using discoveryd mode, iscsid will attempt to login from all iSCSI ifaces found in /var/lib/iscsi/ifaces. If the iface cannot log into the target this will fill the log with failure messages every discoveryd_poll_inval seconds. To prevent this, the iface can be deleted by running "iscsiadm -m iface -o delete -I ifacename".

A change in the 2.6.31 Linux kernel made the net.ipv4.conf.default.rp_filter = 1 more strict in the I/O that is accepted. Consequently, in Red Hat Enterprise Linux 6, if there are multiple interfaces on the same subnet and I/O is sent to the one that is not the default route, the I/O will be dropped. Note that this applies to iSCSI iface binding when multiple interfaces are on the same subnet. To work around this, set the net.ipv4.conf.default.rp_filter parameter in /etc/sysctl.conf to 0 or 2, and reboot the machine.

Attempting to run multiple LVM commands in quick succession might cause a backlog of these commands. Consequently, some of the operations requested might time-out, and subsequently, fail.

dracut currently only supports one FiberChannel over Ethernet (FCoE) connection to be used to boot from the root device. Consequently, booting from a root device that spans multiple FCoE devices (e.g. using RAID, LVM or similar techniques) is not possible.

If an LVM volume requires physical volumes that are multipath or FCoE devices, the LVM volume will not automatically activate. To enable automatic LVM activation, create a udev rules file /etc/udev/rules.d/64-autolvm.rules with the following content:

SUBSYSTEM!="block", GOTO="lvm_end"
ACTION!="add|change", GOTO="lvm_end"
KERNEL=="dm-[0-9]*", ACTION=="add", GOTO="lvm_end"
ENV{ID_FS_TYPE}!="LVM*_member", GOTO="lvm_end"

PROGRAM=="/bin/sh -c 'for i in $sys/$devpath/holders/dm-[0-9]*; do [ -e $$i ] && exit 0; done; exit 1;' ", \
    GOTO="lvm_end"

RUN+="/bin/sh -c '/sbin/lvm vgscan; /sbin/lvm vgchange -a y'"

LABEL="lvm_end"

Note, however that this work around may impact system performance.

The fscontext=, defcontext=, rootcontext= or context= mount options should not be used for remount operations. Using these options can cause the remount of a manually mounted volume to fail, returning errors such as:

mount: /dev/shm not mounted already, or bad option

If the qeth interface was previously configured using system-config-network 1.6.0.el6.2, the "OPTIONS=" line needs to be manually added to /etc/sysconfig/network-scripts/ifcfg-<interface>.

After the configuration has been manually changed, activate the interface by either rebooting the system, or running the following commands:

# /sbin/znet_cio_free
# SUBSYSTEM="ccw" DEVPATH="bus/ccw/devices/<SUBCHANNEL 0>" /lib/udev/ccw_init
# ifup <interface>

A known issue in the bnx2 driver prevents BCM5709S network adapters from performing a vmcore core dump over NFS.

Intel 82575EB ethernet devices do not function in a 32 bit environment. To work around this issue, modify the kernel parameters to include the intel_iommu=off option.

Running the rds-ping command may fail, returning the error:

bind() failed, errno: 99 (Cannot assign requested address).

Note, also that this error may occur even with LOAD_RDS=yes set in /etc/rdma/rdma.conf. To work around this issue, load the rds-tcp module.

Running the command rds-stress on a client may result in the following error attempting to connect to the server:

connecting to <server IP address>:4000: No route to host
connect(<server IP address>) failed#

When configuring a network interface manually, including static IP addresses and search domains, it is possible that a search entry will not be propagated to /etc/resolv.conf. Consequently, short host names that do not include the domain name will fail to resolve. To workaround this issue, add a search entry manually to /etc/resolv.conf.

Under some circumstances, the NetworkManager panel applet cannot determine if a user has permission to enable networking. Consequently, after logging into the desktop, the "Enable Networking" and "Enable Wireless" checkboxes may be disabled. To work around this, run the following command as root:

touch /usr/share/polkit-1/actions/org.freedesktop.NetworkManager.policy

Alternatively, WiFi can be enabled using the command:

nmcli nm wifi on

or disabled using the command:

nmcli nm wifi off

Under some circumstances, the netcf command crashes, returning the error message:

Failed to initialize netcf
error: unspecified error

To work around this issue, set the following value in /etc/sysctl.conf:

   net.bridge.bridge-nf-call-iptables = 0

This issue presents when the augeas library (used by netcf) has trouble parsing one of the system config files that netcf needs to read or modify.

The default value of the Emulex lpfc module parameter, lpfc_use_msi, was 2 (MSI-X) on Red Hat Enterprise Linux 5.4. In Red Hat Enterprise Linux 6 this default is now set to 0 (INTx). This change causes the driver behavior to stop using MSI-X interrupt mode and reverts to using non-msi (INTx) interrupt mode. This change in defaults addresses apparent regressions in some hardware platforms, introduced when the default lpfc driver value was previously changed from 0 to 2 (which made MSI-X the default behavior).

If the lpfc module is behaving erratically, work around this issue by setting the lpfc module parameter lpfc_use_msi to 2.

Supplying an invalid version number in cluster.conf as a parameter to the cman_tool command will cause the cluster to stop processing information. To work around this issue, ensure that the version number used is valid.

Under some circumstances, creating cluster mirrors with the '--nosync' option may cause I/O to become extremely slow. Note that this issue only effects I/O immediately after the creation of the mirror, and only when '--nosync' is used. To work around this issue, run the following command after the creating the mirror.

lvchange --refresh <VG>/<LV>

luci will not function with Red Hat Enterprise Linux 5 clusters unless each cluster node has ricci version 0.12.2-14

The sync state of an inactive LVM mirror cannot be determined. Consequently, the primary device of an LVM mirror can only be removed when the mirror is in-sync.

If device-mapper-multipath is used, and the default path failure timeout value (/sys/class/fc_remote_ports/rport-xxx/dev_loss_tmo) is changed, that the timeout value will revert to the default value after a path fails, and later restored. Note that this issue will present the lpfc, qla2xxx, ibmfc or fnic Fibre Channel drivers. To work around this issue the dev_loss_tmo value must be adjusted after each path fail/restore event.

Generally, placing mirror legs on different physical devices improves data availability. The command lvcreate --alloc anywhere does not guarantee placement of data on different physical devices. Consequently, the use of this option is not recommended. If this option is used, the location of the data placement must be manually verified.

The GFS2 fsck program, fsck.gfs2, currently assumes that the gfs2 file system is divided into evenly-spaced segments known as resource groups. This is always the case on file systems formatted by mkfs.gfs2. It will also be the case for most file systems created as GFS (gfs1) and converted to gfs2 format with gfs2_convert. However, if a GFS file system was resized (with gfs_grow) while it was in the GFS format, the resource groups might not be evenly spaced. If the resource groups are not evenly spaced, and the resource groups or the resource groups index (rindex) become damaged, fsck.gfs2 might not function correctly.

There is currently no workaround for this issue. However, if the resource groups are not damaged, avoid this issue by copying the file system contents to a new device with evenly-spaced resource groups. Format the new device as gfs2 with mkfs.gfs2, and copy the contents from the old device to the new device. The new device will have evenly-spaced resource groups.

Enabling user authentication against an LDAP server using authconfig --enableldapauth does not correctly set up the /etc/nslcd.conf configuration file. Consequently, LDAP users will be denied access to the system. To work around this issue, remove the line containing pam_password md5 from the /etc/nslcd.conf file.

The System Security Services Daemon (SSSD) currently supports following LDAP referrals on anonymous-bind LDAP connections only.

The authentication configuration utility does not keep the 'Require smart card for login' check box set when Kerberos is also enabled. When the check box is checked and the configuration is saved with the 'Apply' button, the system will correctly require smart card for login. However, on the subsequent run of the authentication configuration utility the check box will be unchecked again and it is necessary to check it again to keep the option switched on.

When attempting to perform PKINIT pre-authentication, if the client has more than one possible candidate certificate the client may fail to select the certificate and key to use. This usually occurs if certificate selection is configured to use the value of the keyUsage extension, or if any of the candidate certificates does not contain a subjectAltName extension. Consequently, the client attempts to perform pre-authentication using a different (usually password-based) mechanism.

After installing certmonger, the system message bus daemon needs to be signaled to reload its configuration to allow the certmonger service to start properly. To work around this issue, send the dbus-daemon process a SIGHUP signal, or, alternatively, reboot the system.

The udev daemon in Red Hat Enterprise 6 watches all devices for changes. If a change occurs, the device is rescanned for device information to be stored in the udev database.

The scanning process causes additional I/O to devices after they were changed by tools. udev to can be told to exclude devices from being watched with a udev rule. A rule can be created by adding a new file <myname>.rules in /etc/udev/rules.d containing the following line:

ACTION=="add|change", SYMLINK=="disk/by-id/scsi-SATA_SAMSUNG_HD400LDS0AXJ1LL903246", OPTIONS+="nowatch"

The SYMLINK should be replaced with any symlink path found in /dev/disk/* for the device in question.

This will prevent unexpected I/O on the device, after data was written directly to the device (not on the filesystem). However, it will also prevent device updates in the udev database, like filesystem labels, symbolic links in /dev/disk/*, etc.

Under some circumstances, the bfa-firmware package in Red Hat Enterprise Linux 6 may cause these devices to encounter a rare memory parity error. To work around this issue, to update to the newer firmware package, available directly from Brocade.

Red Hat Enterprise Linux 6 only has support for the first revision of the UPEK Touchstrip fingerprint reader (USB ID 147e:2016). Attempting to use a second revision device may cause the fingerprint reader daemon to crash. The command

lsusb -v -d 147e:2016 | grep bcdDevice

will return the version of the device being used in an individual machine.

The Emulex Fibre Channel/Fibre Channel-over-Ethernet (FCoE) driver in Red Hat Enterprise Linux 6 does not support DH-CHAP authentication. DH-CHAP authentication provides secure access between hosts and mass storage in Fibre-Channel and FCoE SANs in compliance with the FC-SP specification. Note, however that the Emulex driver (lpfc) does support DH-CHAP authentication on Red Hat Enterprise Linux 5, from version 5.4. Future Red Hat Enterprise Linux 6 releases may include DH-CHAP authentication.

Partial Offload iSCSI adapters do not work on Red Hat Enterprise Linux. Consequently, devices that use the be2iscsi driver cannot be used during installation.

The hpsa_allow_any kernel option allows the hpsa driver to be used with older hardware that typically uses the cciss module by default. To use the hpsa driver with older hardware, set hpsa_allow_any=1 and blacklist the cciss module. Note, however that this is an unsupported, non-default configuration.

Platforms with BIOS/UEFI that are unaware of PCI-e SR-IOV capabilities may fail to enable virtual functions

The recommended minimum HBA firmware revision for use with the mpt2sas driver is "Phase 5 firmware" (i.e. with version number in the form 05.xx.xx.xx.) Note that following this recommendation is especially important on complex SAS configurations involving multiple SAS expanders.

The persistent naming of devices that are dynamically discovered in a system is a large problem that exists both in and outside of kdump. Nominally, devices are detected in the same order, which leads to consistent naming. In cases where devices are not detected in the same order, device abstraction layers (e.g. LVM) make essentially resolve the issue, though the use of metadata stored on the devices to create consistency. In the rare cases where no such abstraction layer is in use, and renaming devices causes issues with kdump, it is recommended that devices be referred to by disk label or UUID in kdump.conf.

The following issues and limitations may be encountered with the Broadcom bnx2, bnx2x, and cnic drivers

Calgary IOMMU default detection has been disabled in this release. If you require Calgary IOMMU support add 'iommu=calgary' as a boot parameter.

The kdump service fails on systems with large amounts of memory and crashkernel=auto enabled, returning the error message kdump: kexec: failed to load kdump kernel in /var/log/messages.

To workaround this issue, change the crashkernel parameter to 128M (on x86_64 and x86 architectures) or 256M (on the ppc64 architecture).

If the kdump crash recovery technology is enabled and in use on a given system, minimum memory requirements should be raised by the amount of memory reserved for kdump usage. This value is determined by the user, and specified on the kernel command line, via the crashkernel parameter. The default value for this setting is 128MB.

When using the DIF/DIX hardware checksum features of a storage path behind a block device, errors will occur if the block device is used as a general purpose block device.

Buffered I/O or mmap(2) based IO will not work reliably as there are no interlocks in the buffered write path to prevent overwriting cached data while the hardware is performing DMA operations. An overwrite during a DMA operation will cause a torn write and the write will fail checksums in the hardware storage path. This problem is common to all block device or file system based buffered or mmap(2) I/O, so the problem of I/O errors during overwrites cannot be worked around.

DIF/DIX enabled block devices should only be used with applications that use O_DIRECT I/O. Applications should use the raw block device, though it should be safe to use the XFS file system on a DIF/DIX enabled block device if only O_DIRECT I/O is issued through the file system. In both cases the responsibility for preventing torn writes lies with the application, so only applications designed for use with O_DIRECT I/O and DIF/DIX hardware should enable this feature.

The memory controller in Red Hat Enterprise Linux 6 beta may encounter stability issues when under heavy stress testing or memory pressure.

The i686 debug kernel may crash on some systems when starting the udev service.

Systems configured with Intel 82578DM NICs may not be recognized during boot/install resulting in driver load failure, (driver probe fails with error -2).

This pre-release version of Red Hat Enterprise Linux 6 provides automated Physical CPU Socket and Memory Hot-Add support. Note, however, that CPU Socket and Memory Hot-Remove actions are not supported. Additionally, only single CPU Socket add events are supported at this time, and tsc support is disabled after a CPU Socket add event.

In Beta releases of Red Hat Enterprise Linux 6, PCIe ASPM would be enabled on PCIe hierarchies even if they lacked an _OSC method as defined in section 4.5 of the PCI firmware specification, release 3.0. Post Beta, firmware must provide an appropriate _OSC method on all PCI roots in order to allow PCIe ASPM to be enabled. The "pcie_aspm=force" boot parameter may be passed in order to enable PCIe ASPM.

Use of the cciss and hpsa drivers with some controllers (e.g. P400, P400i, E500, P800, P700m and 6402/6404) may cause kdump to fail.

The top-level makefile to of the kernel in Red Hat Enterprise Linux 6 includes the -Werror option as part of the standard kernel build. Consequently, all kernel compile warnings are reported as errors. In non-production environments, the -Werror flag can be disabled by removing the following two lines from the top-level kernel Makefile:

KBUILD_CFLAGS   += $(shell if [ $(CPP_VERS) -ge 4004004 ]; then \
                 echo "-Wno-array-bounds -Werror"; else echo ""; fi)

Note, however, that Red Hat does not support custom built kernels or custom built modules.

Some SystemTap probes require the additional module, uprobes.ko at run time. This additional module is usually built automatically when the script is compiled. However, in the client-server case, the uprobes.ko module is not returned by the server to the client. Consequently, missing symbols are reported when the module representing the script is loaded. To work around this issue, use the following command to manually build the uprobes.ko module on the client host.

  make -C <prefix>/share/systemtap/runtime/uprobes

Note that "<prefix>" is the install prefix for systemtap, and that this manual build of uprobes.ko will only need to be done once.

Due to the way ftrace works when modifying the code during startup, the NMI watchdog causes too much noise and ftrace can not find a quiet period to instrument the code. Consequently, machines with more than 512 cpus will encounter issues with the NMI watchdog. Such issues will return error messages similar to "BUG: NMI Watchdog detected LOCKUP" and have either 'ftrace_modify_code' or 'ipi_handler' in the backtrace. To work around this issue, disable nmi_watchdog using the command:

nmi_watchdog=0

Under some circumstances, a kernel panic on installation or boot may occur if the "Interrupt Remapping" feature is enabled in the BIOS. To work around this issue, disable interrupt remapping in the BIOS.

The kernel will panic when booting the kdump kernel on a s390 system with an initramfs that contains an odd number of bytes. To work around this this issue, generate an initramfs with sufficient padding such that it contains an even number of bytes.

Creating many 'cpu' control groups (cgroups) on a system with a large number of CPUs will slow down the machine when the control groups feature is enabled. To work around this issue, disable control groups.

Under certain circumstances, the Linux kernel makes an erroneous assumption about where to reserve memory for the kdump kernel on large-memory POWER systems. Consequently, a newly installed POWER system may return the following message during the initial post installation bootup:

returning from prom_init
 Kernel panic - not syncing: ERROR: Failed to allocate 0x4000 bytes below 0x10000000.
 Rebooting in 180 seconds..

Complete the following steps to work around this issue. Note, however, that this work around disables the kdump feature.

On 64-bit POWER systems the EHEA NIC driver will fail when attempting to dump a vmcore via NFS. To work around this issue, utilize other kdump facilities, for example dumping to the local filesystem, or dumping over SSH.

A BIOS emulated floppy disk might cause the installation or kernel boot process to hang. To avoid this, disable emulated floppy disk support in the BIOS.

The preferred method to enable nmi_watchdog on 32-bit x86 systems is to use either nmi_watchdog=2 or nmi_watchdog=lapic parameters. The parameter nmi_watchdog=1 is not supported.

The module loading operation of certain crypto libraries will not be successful. Consequently, the modules required for in-kernel crypto cannot be loaded. In-kernel crypto cannot be used with Red Hat Enterprise Linux 6 until this issue is resolved.

A BIOS issue on some platforms incorrectly indicates that the system busmastering flag must be checked before entering the deep C state. Consequently, some systems might spend a significantly lower percentage of time in deep C states (C3 and lower) in Red Hat Enterprise Linux 6 compared to Red Hat Enterprise Linux 5.5. Updated the BIOS on affected systems will resolve this issue.

IMA in Red Hat Enterprise Linux 6.0 GA is enabled by loading an IMA policy. However, future updates will require the boot parameter "ima=on" in addition to loading an IMA policy to enable IMA. This change reduces overhead on systems not using IMA.

cURL is a tool for getting files from FTP, HTTP, Gopher, Telnet, and Dict servers, using any of the supported protocols. The cURL API, and consequently, the python bindings for cURL, do not provide textual messages for errors. Therefore, all applications that use the python bindings for cURL will return errors in formats such as:

 Pycurl Error 6 - ""

instead of more useful messages such as:

 Pycurl Error 6 - "Could not resolve hostname: blah.example.com"

cURL error codes can be manually interpreted by reading the /usr/include/curl/curl.h file.

Due to a deficiency in java-1.6.0-ibm-plugin for AMD64 and Intel 64, IBM Java 6 Web Start cannot open JNLP files. This affects file management tools and WWW browsers. To work around this open JNLP files using the command:

/usr/lib/jvm/jre-1.6.0-ibm.x86_64/bin/javaws file.jnpl

Note that 32-bit packages are not affected by this issue.

Under some circumstances on the PPC64 architecture, Ruby does not save the context correctly when switching threads. Consequently, when a thread is restored it has a stale value which might return a architecture fault.

Under some circumstances, libdfp encounters an issue converting some values from string to DFP with the conversion command strtod32. The strtod64 and strtod128 commands do work correctly.

When enabled, fingerprint authentication is the default authentication method to unlock a workstation, even if the fingerprint reader device is not accessible. However, after a 30 second wait, password authentication will become available.

ATI RN50/ES1000 graphics devices have limited Video RAM (VRAM) and are restricted to an 8-bit color depth for the text console. Consequently, the graphical boot screen is unavailable on systems using these graphics devices.

On the GNOME desktop, the CD/DVD burning utility brasero conflicts with the automounting feature in Nautilus. Consequently, the following error message will be displayed when brasero attempts to verify the checksum of the disc:

Error while burning: You do not have the required permissions to use this drive

In most cases, the data is still written to the disc.

The system-config-users tool cannot always detect if a home directory can be created correctly. Consequently, system-config-users might fail silently when attempting to create a home directory on some file systems (e.g. home directories located beneath an autofs mount-point). Typically, when this issue is encountered, the user account itself is created, but the creation of the home directory fails. To create a user with an auto-mounted home directory, create the home directory manually before creating the user in system-config-users.

Evolution's IMAP backend only refreshes folder contents under the following circumstances: when the user switches into or out of a folder, when the auto-refresh period expires, or when the user manually refreshes a folder (i.e. using the menu item Folder > Refresh). Consequently, when replying to a message in the Sent folder, the new message does not immediately appear in the Sent folder. To see the message, force a refresh using one of the methods describe above.

Not all languages have predefined default input method engines. Consequently, in some languages, ibus will not have an input method engine configured. To work around this issue, add an input method using the Input Method configuration dialog (System > Preferences > Input Method

Using the im-chooser tool, XIM cannot be disabled as the default GTK immodule. Disabling input-methods using im-chooser and restarting the desktop session will still result in GTK applications using the XIM immodule. Consequently, using the Ctrl+Shift+U key combination to the directly input of Unicode characters from their hexidecimal code will not work. To work around this issue, use im-chooser to enable ibus. Enabling ibus permits gtk-im-context-simple's Unicode input and compose sequences to be used.

The hardware mute button on Lenovo ThinkPad X200 notebooks does not work. Note, however, that the volume down and volume up buttons function correctly.

The clock applet in the GNOME panel has a default location of Boston, USA. Additional locations are added by via the applet's preferences dialog. Additionally, to change the default location, left-click the applet, hover over the desired location in the "Locations" section, and click the "Set..." button that appears.

In some multi-monitor configurations (e.g. dual monitors with both rotated), the cursor confinement code produces incorrect results. For example, the cursor may be permitted to disappear offscreen when it should not, or be prevented from entering some areas where it should be allowed to go. Currently, the only work around to this issue is to disable monitor rotation.

ATI RN50/ES1000 graphics devices have a lower number of hardware controllers than output connectors. Due to a defect in the graphical boot system, this type of configuration results in a blank display. Consequently, users of systems with these ATI graphics devices will experience prolonged (potentially up to 2 minutes or longer) blank screens during boot up and shutdown. Once the boot process completes and a login prompt is available, the display will function as expected. The prolonged blank screen can be avoided by removing "rhgb" from the list of boot parameters on the kernel command line in /etc/grub.conf

If a Russian keyboard is chosen during system installation, the login screen is configured to use Russian input for user names and passwords by default. However, pressing Left Shift and Right Shift does not cause the input to change to ASCII mode. Consequently, the user cannot log in. To work around this issue, run the following sequence, as root, post installation:

. /etc/sysconfig/keyboard; echo $LAYOUT | grep -q ",us" && gconftool-2
--direct --config-source xml:readwrite:/var/lib/gdm/.gconf --set
/apps/gdm/simple-greeter/recent-layouts --type list --list-type string $(echo
$LAYOUT | awk -F, '{ print "[" $2 "," $1 "]"; }') && echo "DONE"

For KMS drivers, the syntax is:

video=[connector:]mode

"connector", which is optional maps to the name of the connector as listed in /sys/class/drm/card0. For example:

~% ls /sys/class/drm/card0 
card0-LVDS-1  card0-VGA-1  dev  device  power  subsystem  uevent

This device has connectors named LVDS-1 and VGA-1. If no connector is specified the requested mode will apply to all connectors.

Mode strings may be of the form:

<xres>x<yres>[R][-<bpp>][@<refresh>][i][eDd]

Parts inside <> are mandatory, parts inside [] are optional. R requests the use of the CVT reduced-blanking formula, applicable for some digital displays; otherwise GTF is used. i requests an interlaced mode. e forces the output to be enabled even if it appears to be disconnected; d forces the output to be disabled. For DVI connections, D forces the use of the digital signal path instead of analog; on other connectors it has no effect. Only one of e, d, or D may be given.

Under some circumstances, the Add/Remove Software (gpk-application) graphical user interface does not display Supplementary groups or packages the Supplementary group is chosen. To work around this, use the System>Refresh Package Lists option to refresh the package lists.