The new Linux kernel version provides different drivers for some PATA (IDE) controllers. The names of some hard disk, CD-ROM, and tape devices may change.

It is now recommended to identify disk devices in configuration files by label or UUID (unique identifier) rather than by device name, which will work with both old and new kernel versions. Upon upgrading to the squeeze version of the Debian kernel packages, the linux-base package will offer to do this conversion for you in the config files for most of the filesystem-related packages on the system, including the various bootloaders included in Debian. If you choose not to update the system configuration automatically, or if you are not using the Debian kernel packages, you must update device IDs yourself before the next system reboot to ensure the system remains bootable.

The following only applies to users who want to let the grub-pc bootloader load the kernel directly off a RAID device created with mdadm 3.x and default values, or when the metadata version is explicitly set using -e. Specifically, this includes all arrays created during or after the installation of Debian squeeze. Arrays created with older mdadm versions, and RAIDs created with the command-line option -e 0.9 are not affected.

Versions of grub-pc older than 1.98+20100720-1 will not be able to boot directly off a RAID with the 1.x metadata formats (the new default is 1.2). To ensure a bootable system, please make sure to use grub-pc 1.98+20100720-1 or later, which is provided by Debian squeeze. An unbootable system may be rescued with Super Grub2 Disk or grml.

If you installed Xen on lenny, the default kernel booted by GRUB Legacy was the one providing a Xen hypervisor and dom0 support. This behavior has changed with GRUB 2 in squeeze: the non-Xen kernel will boot by default. If you need Xen and expect to boot with it by default, there are configuration hints at http://wiki.debian.org/Xen#Installationandconfiguration.

Upgrades from lenny will not automatically install Xen version 4.0. You should install the xen-linux-system-2.6-xen-amd64 or xen-linux-system-2.6-xen-686 package to ensure the Xen hypervisor and suitable dom0 kernel are installed, and to make future upgrades easier.

Squeeze's 2.6.32 Xen kernel uses pvops instead of the forward-ported Xenlinux patch. This means that on squeeze your domU won't be able to use (for example) sda1 as a device name for its hard drive, since this naming scheme is not available under pvops. Instead you should use (as a corresponding example) xvda1, which is compatible with both old and new Xen kernels.

Some Berkeley Database version 7 files created with libdb3 cannot be read by newer libdb versions (see bug #521860). As a workaround, the files can be recreated with db4.8_load, from the db4.8-util package.

If you have previously added a local diversion for /bin/sh, or modified the /bin/sh symlink to point to somewhere other than /bin/bash, then you may encounter problems when upgrading the dash or bash packages. Note that this includes changes made by allowing other packages (for example mksh) to become the default system shell by taking over /bin/sh.

If you encounter any such issues, please remove the local diversion and ensure that the symlinks for both /bin/sh and its manual page point to the files provided by the bash package and then dpkg-reconfigure --force dash.

    dpkg-divert --remove /bin/sh
    dpkg-divert --remove /usr/share/man/man1/sh.1.gz
    
    ln -sf bash /bin/sh
    ln -sf bash.1.gz /usr/share/man/man1/sh.1.gz
  

The default setting for the acpi_enforce_resources parameter in the Linux kernel has changed to be “strict” by default. This can lead some legacy sensor drivers to be denied access to the sensors' hardware. One workaround is to append “acpi_enforce_resources=lax” to the kernel command line.

KDE 3 Desktop Environment is no longer supported in Debian 6.0. It will be automatically replaced by the new 4.4 series on upgrade. As this is a major change, users should take some precautions in order to ensure as smooth of an upgrade process as possible.

	Important
	It is discouraged to upgrade while there is an active KDE 3 session on the system. Otherwise, the process might render the running session dysfunctional with the possibility of data loss.

Upon the first login on the upgraded system, existing users will be prompted with the Debian-KDE guided migration procedure called kaboom which will assist in the process of migrating the user's personal data and optionally backing up old KDE configuration. For more information, visit the Kaboom homepage.

While KDE 3 based desktop environment is no longer supported, users can still install and use some individual KDE 3 applications since the core libraries and binaries of KDE 3 (kdelibs) and Qt 3 are still available in Debian 6.0. However, please note that these applications might not be well integrated with the new environment. What's more, neither KDE 3 nor Qt 3 will be supported in any form in the next Debian release so if you are using them, you are strongly advised to port your software to the new platform.

As noted earlier, Debian 6.0 introduces a new set of KDE related metapackages:

The GNOME Display Manager (GDM), is kept at version 2.20 for systems upgraded from lenny. This version will still be maintained for the squeeze cycle but it is the last release to do so. Newly installed systems will get GDM 2.30 instead, provided by the gdm3 package. Because of incompatibilities between both versions, this upgrade is not automatic, but it is recommended to install gdm3 after the upgrade to squeeze. This should be done from the console, or with only one open GNOME session. Note that settings from GDM 2.20 will not be migrated. For a standard desktop system, however, simply installing gdm3 should be enough.

Specific permissions on devices are granted automatically to the user currently logged on physically to the system: video and audio devices, network roaming, power management, device mounting. The cdrom, floppy, audio, video, plugdev and powerdev groups are no longer useful. See the consolekit documentation for more information.

Most graphical programs requiring root permissions now rely on PolicyKit to do so, instead of gksu. The recommended way to give a user administrative rights is to add it to the sudo group.

Upon upgrading the network-manager package, interfaces configured in /etc/network/interfaces to use DHCP with no other options will be disabled in that file, and handled by NetworkManager instead. Therefore the ifup and ifdown commands will not work. These interfaces can be managed using the NetworkManager frontends instead, see the NetworkManager documentation.

Conversely, any interfaces configured in /etc/network/interfaces with more options will be ignored by NetworkManager. This applies in particular to wireless interfaces used during the installation of Debian (see bug #606268).

The cyrix, imstt, sunbw2 and vga Xorg video drivers are no longer provided. Users should switch to a generic such as vesa or fbdev instead.

The old via driver was no longer maintained, and has been replaced by the openchrome driver, which will be used automatically after the upgrade.

The nv and radeonhd drivers are still present in this release, but are deprecated. Users should consider the nouveau and radeon drivers instead, respectively.

The calcomp, citron, digitaledge, dmc, dynapro, elo2300, fpit, hyperpen, jamstudio, magellan, microtouch, mutouch, palmax, spaceorb, summa, tek4957 and ur98 X input drivers have been discontinued and are not included in this release. Users of these devices might want to switch to a suitable kernel driver and the evdev X driver. For many serial devices, the inputattach utility allows attaching them to a Linux input device which can be recognized by the evdev X driver.

Kernel drivers for Intel (starting from i830), ATI/AMD (from the original Radeon to the Radeon HD 5xxx “Evergreen” series) and for NVIDIA graphics chipsets now support native mode setting.

Support for old-style userspace mode setting is discontinued in the intel X driver, which requires a recent kernel. Users of custom kernels should make sure that their configuration includes CONFIG_DRM_I915_KMS=y.

The Xorg X server included in Debian 6.0 provides improved support for hotplugging of input devices (mice, keyboards, tablets, …). The old xserver-xorg-input-kbd and xserver-xorg-input-mouse packages are replaced by xserver-xorg-input-evdev, which requires a kernel with the CONFIG_INPUT_EVDEV option enabled. Additionally, some of the keycodes produced by this driver differ from those traditionally associated with the same keys. Users of programs like xmodmap and xbindkeys will need to adjust their configurations for the new keycodes.

Traditionally, the Ctrl+Alt+Backspace combination would kill the X server. This combination is no longer active by default, but can be re-enabled by reconfiguring the keyboard-configuration package (system-wide), or using your desktop environment's keyboard preferences application.