43.2 Kernel Versions

Debian provides a very simple approach to upgrading (or downgrading) kernels. Kernels are simply packaged as Debian packages and installed in the usual way (see Section ??).

Note that Debian treats kernel versions as different packages. Thus, installing kernel-image-2.4.9-1-686-smp installs a different package to kernel-image-2.4.6-1-686-smp. You can have multiple kernels installed at any time, however only one kernel is ever chosen at boot time (and you can have the choice, although a default will be chosen each boot). The advantage of this is that you can be confident to install a new (perhaps experimental) version of a kernel and reboot into that version, but always be assured that you can go back to a previous version if there are problems with the newer version. Old versions hang around until you explicitly remove them.

It should also be noted that within specific package versions (e.g., kernel-image-2.4.9-1-686-smp) there are also normal Debian package versions (e.g., 2.6.9-2). Potentially, you may be installing an update of a currently running kernel, as in updating kernel-image-2.4.9-1-686-smp from version 2.6.9-1 to 2.6.9-2. Some complications can arise when installing an update of the current version of a kernel. A message may appear indicating that you are upgrading the current kernel and the modules will be overwritten. As the message will indicate, you should reboot your computer as soon as possible, since these modules are probably currently being used by the kernel!

43.2.1 2.6.9-1-686-smp

Installed 12 November 2004 as package kernel-image-2.6.9-1-686-smp. Digital camera USB connection and USB Flash drive fail to be recognised as previously: Plug in the camera and dmesg gives:

  usb 1-1: new full speed USB device using address 5
  ubb: device 5 capacity nsec 246017 bsize 512
  ubb: was not changed
   /dev/ub/b: p1

With kernel-image-2.6.7-1-686-smp dmesg reported:

  usb 1-1: new full speed USB device using address 4
  scsi4 : SCSI emulation for USB Mass Storage devices
    Vendor:  hp       Model: photosmart 320    Rev: 100
    Type:   Direct-Access                      ANSI SCSI revision: 02
  SCSI device sdc: 246017 512-byte hdwr sectors (126 MB)
  sdc: assuming Write Enabled
  sdc: assuming drive cache: write through
   /dev/scsi/host4/bus0/target0/lun0: p1
  Attached scsi removable disk sdc at scsi4, channel 0, id 0, lun 0
  USB Mass Storage device found at 4

and the device was mounted as /dev/sdc1. After moving to udev (see Section 54.7) things started working as expected.

43.2.2 2.6

The 2.6 kernel has improved scheduling.



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