Chapter 4. Upgrades from Debian 9 (stretch)

Table of Contents

4.1. Preparing for the upgrade
4.1.1. Back up any data or configuration information
4.1.2. Inform users in advance
4.1.3. Prepare for downtime on services
4.1.4. Prepare for recovery
4.1.5. Prepare a safe environment for the upgrade
4.1.6. Verify network interface name support
4.2. Checking APT configuration status
4.2.1. The proposed-updates section
4.2.2. Unofficial sources
4.2.3. Disabling APT pinning
4.2.4. Checking packages status
4.3. Preparing APT source-list files
4.3.1. Adding APT Internet sources
4.3.2. Adding APT sources for a local mirror
4.3.3. Adding APT sources from optical media
4.4. Upgrading packages
4.4.1. Recording the session
4.4.2. Updating the package list
4.4.3. Make sure you have sufficient space for the upgrade
4.4.4. Minimal system upgrade
4.4.5. Upgrading the system
4.5. Possible issues during upgrade
4.5.1. Dist-upgrade fails with Could not perform immediate configuration
4.5.2. Expected removals
4.5.3. Conflicts or Pre-Depends loops
4.5.4. File conflicts
4.5.5. Configuration changes
4.5.6. Change of session to console
4.6. Upgrading your kernel and related packages
4.6.1. Installing a kernel metapackage
4.7. Preparing for the next release
4.7.1. Purging removed packages
4.8. Obsolete packages
4.8.1. Transitional dummy packages

4.1. Preparing for the upgrade

We suggest that before upgrading you also read the information in Chapter 5, Issues to be aware of for buster. That chapter covers potential issues which are not directly related to the upgrade process but could still be important to know about before you begin.

4.1.1. Back up any data or configuration information

Before upgrading your system, it is strongly recommended that you make a full backup, or at least back up any data or configuration information you can't afford to lose. The upgrade tools and process are quite reliable, but a hardware failure in the middle of an upgrade could result in a severely damaged system.

The main things you'll want to back up are the contents of /etc, /var/lib/dpkg, /var/lib/apt/extended_states and the output of dpkg --get-selections "*" (the quotes are important). If you use aptitude to manage packages on your system, you will also want to back up /var/lib/aptitude/pkgstates.

The upgrade process itself does not modify anything in the /home directory. However, some applications (e.g. parts of the Mozilla suite, and the GNOME and KDE desktop environments) are known to overwrite existing user settings with new defaults when a new version of the application is first started by a user. As a precaution, you may want to make a backup of the hidden files and directories (dotfiles) in users' home directories. This backup may help to restore or recreate the old settings. You may also want to inform users about this.

Any package installation operation must be run with superuser privileges, so either log in as root or use su or sudo to gain the necessary access rights.

The upgrade has a few preconditions; you should check them before actually executing the upgrade.

4.1.2. Inform users in advance

It's wise to inform all users in advance of any upgrades you're planning, although users accessing your system via an ssh connection should notice little during the upgrade, and should be able to continue working.

If you wish to take extra precautions, back up or unmount the /home partition before upgrading.

You will have to do a kernel upgrade when upgrading to buster, so a reboot will be necessary. Typically, this will be done after the upgrade is finished.

4.1.3. Prepare for downtime on services

There might be services that are offered by the system which are associated with packages that will be included in the upgrade. If this is the case, please note that, during the upgrade, these services will be stopped while their associated packages are being replaced and configured. During this time, these services will not be available.

The precise downtime for these services will vary depending on the number of packages being upgraded in the system, and it also includes the time the system administrator spends answering any configuration questions from package upgrades. Notice that if the upgrade process is left unattended and the system requests input during the upgrade there is a high possibility of services being unavailable[1] for a significant period of time.

If the system being upgraded provides critical services for your users or the network[2], you can reduce the downtime if you do a minimal system upgrade, as described in Section 4.4.4, “Minimal system upgrade”, followed by a kernel upgrade and reboot, and then upgrade the packages associated with your critical services. Upgrade these packages prior to doing the full upgrade described in Section 4.4.5, “Upgrading the system”. This way you can ensure that these critical services are running and available through the full upgrade process, and their downtime is reduced.

4.1.4. Prepare for recovery

Although Debian tries to ensure that your system stays bootable at all times, there is always a chance that you may experience problems rebooting your system after the upgrade. Known potential issues are documented in this and the next chapters of these Release Notes.

For this reason it makes sense to ensure that you will be able to recover if your system should fail to reboot or, for remotely managed systems, fail to bring up networking.

If you are upgrading remotely via an ssh link it is recommended that you take the necessary precautions to be able to access the server through a remote serial terminal. There is a chance that, after upgrading the kernel and rebooting, you will have to fix the system configuration through a local console. Also, if the system is rebooted accidentally in the middle of an upgrade there is a chance you will need to recover using a local console.

For emergency recovery we generally recommend using the rescue mode of the buster Debian Installer. The advantage of using the installer is that you can choose between its many methods to find one that best suits your situation. For more information, please consult the section Recovering a Broken System in chapter 8 of the Installation Guide and the Debian Installer FAQ.

If that fails, you will need an alternative way to boot your system so you can access and repair it. One option is to use a special rescue image or a Linux live CD. After booting from that, you should be able to mount your root file system and chroot into it to investigate and fix the problem.

4.1.4.1. Debug shell during boot using initrd

The initramfs-tools package includes a debug shell[3] in the initrds it generates. If for example the initrd is unable to mount your root file system, you will be dropped into this debug shell which has basic commands available to help trace the problem and possibly fix it.

Basic things to check are: presence of correct device files in /dev; what modules are loaded (cat /proc/modules); output of dmesg for errors loading drivers. The output of dmesg will also show what device files have been assigned to which disks; you should check that against the output of echo $ROOT to make sure that the root file system is on the expected device.

If you do manage to fix the problem, typing exit will quit the debug shell and continue the boot process at the point it failed. Of course you will also need to fix the underlying problem and regenerate the initrd so the next boot won't fail again.

4.1.4.2. Debug shell during boot using systemd

If the boot fails under systemd, it is possible to obtain a debug root shell by changing the kernel command line. If the basic boot succeeds, but some services fail to start, it may be useful to add systemd.unit=rescue.target to the kernel parameters.

Otherwise, the kernel parameter systemd.unit=emergency.target will provide you with a root shell at the earliest possible point. However, this is done before mounting the root file system with read-write permissions. You will have to do that manually with:

# mount -o remount,rw /
      

More information on debugging a broken boot under systemd can be found in the Diagnosing Boot Problems article.

4.1.5. Prepare a safe environment for the upgrade

[Important]Important

If you are using some VPN services (such as tinc) consider that they might not be available throughout the upgrade process. Please see Section 4.1.3, “Prepare for downtime on services”.

In order to gain extra safety margin when upgrading remotely, we suggest that you run upgrade processes in the virtual console provided by the screen program, which enables safe reconnection and ensures the upgrade process is not interrupted even if the remote connection process temporarily fails.

4.1.6. Verify network interface name support

Systems upgraded from older releases that still use network interfaces with names like eth0 or wlan0 are at risk of losing networking once they switch to buster; see Section 5.1.5, “Migrating from legacy network interface names” for migration instructions.

4.2. Checking APT configuration status

The upgrade process described in this chapter has been designed for pure Debian stable systems. If your APT configuration mentions additional sources besides stretch, or if you have installed packages from other releases or from third parties, then to ensure a reliable upgrade process you may wish to begin by removing these complicating factors.

The main configuration file that APT uses to decide what sources it should download packages from is /etc/apt/sources.list, but it can also use files in the /etc/apt/sources.list.d/ directory - for details see sources.list(5). If your system is using multiple source-list files then you will need to ensure they stay consistent.

Below there are two methods for finding installed packages that did not come from Debian, using either aptitude or apt-forktracer. Please note that neither of them are 100% accurate (e.g. the aptitude example will list packages that were once provided by Debian but no longer are, such as old kernel packages).

$ aptitude search '~i(!~ODebian)'
$ apt-forktracer | sort
  

Direct upgrades from Debian releases older than 9 (stretch) are not supported. Please follow the instructions in the Release Notes for Debian 9 to upgrade to Debian 9 first.

This procedure also assumes your system has been updated to the latest point release of stretch. If you have not done this or are unsure, follow the instructions in Section A.1, “Upgrading your stretch system”.

You should also make sure the package database is ready before proceeding with the upgrade. If you are a user of another package manager like aptitude or synaptic, review any pending actions. A package scheduled for installation or removal might interfere with the upgrade procedure. Note that correcting this is only possible if your APT source-list files still point to stretch and not to stable or buster; see Section A.2, “Checking your APT source-list files”.

It is a good idea to remove obsolete packages from your system before upgrading.

4.2.1. The proposed-updates section

If you have listed the proposed-updates section in your APT source-list files, you should remove it before attempting to upgrade your system. This is a precaution to reduce the likelihood of conflicts.

4.2.2. Unofficial sources

If you have any non-Debian packages on your system, you should be aware that these may be removed during the upgrade because of conflicting dependencies. If these packages were installed by adding an extra package archive in your APT source-list files, you should check if that archive also offers packages compiled for buster and change the source item accordingly at the same time as your source items for Debian packages.

Some users may have unofficial backported newer versions of packages that are in Debian installed on their stretch system. Such packages are most likely to cause problems during an upgrade as they may result in file conflicts[4]. Section 4.5, “Possible issues during upgrade” has some information on how to deal with file conflicts if they should occur.

4.2.3. Disabling APT pinning

If you have configured APT to install certain packages from a distribution other than stable (e.g. from testing), you may have to change your APT pinning configuration (stored in /etc/apt/preferences and /etc/apt/preferences.d/) to allow the upgrade of packages to the versions in the new stable release. Further information on APT pinning can be found in apt_preferences(5).

4.2.4. Checking packages status

Regardless of the method used for upgrading, it is recommended that you check the status of all packages first, and verify that all packages are in an upgradable state. The following command will show any packages which have a status of Half-Installed or Failed-Config, and those with any error status.

# dpkg --audit
    

You could also inspect the state of all packages on your system using aptitude or with commands such as

# dpkg -l | pager
    

or

# dpkg --get-selections "*" > ~/curr-pkgs.txt
    

It is desirable to remove any holds before upgrading. If any package that is essential for the upgrade is on hold, the upgrade will fail.

Note that aptitude uses a different method for registering packages that are on hold than apt and dselect. You can identify packages on hold for aptitude with

# aptitude search "~ahold" 
    

If you want to check which packages you had on hold for apt, you should use

# dpkg --get-selections | grep 'hold$'
    

If you changed and recompiled a package locally, and didn't rename it or put an epoch in the version, you must put it on hold to prevent it from being upgraded.

The hold package state for apt can be changed using:

# echo package_name hold | dpkg --set-selections
    

Replace hold with install to unset the hold state.

If there is anything you need to fix, it is best to make sure your APT source-list files still refer to stretch as explained in Section A.2, “Checking your APT source-list files”.

4.3. Preparing APT source-list files

Before starting the upgrade you must reconfigure APT's source-list files (/etc/apt/sources.list and files under /etc/apt/sources.list.d/).

APT will consider all packages that can be found via any configured archive, and install the package with the highest version number, giving priority to the first entry in the files. Thus, if you have multiple mirror locations, list first the ones on local hard disks, then CD-ROMs, and then remote mirrors.

A release can often be referred to both by its codename (e.g. stretch, buster) and by its status name (i.e. oldstable, stable, testing, unstable). Referring to a release by its codename has the advantage that you will never be surprised by a new release and for this reason is the approach taken here. It does of course mean that you will have to watch out for release announcements yourself. If you use the status name instead, you will just see loads of updates for packages available as soon as a release has happened.

Debian provides two announcement mailing lists to help you stay up to date on relevant information related to Debian releases:

4.3.1. Adding APT Internet sources

On new installations the default is for APT to be set up to use the Debian APT CDN service, which should ensure that packages are automatically downloaded from a server near you in network terms. As this is a relatively new service, older installations may have configuration that still points to one of the main Debian Internet servers or one of the mirrors. If you haven't done so yet, it is recommended to switch over to the use of the CDN service in your APT configuration.

To make use of the CDN service, add a line like this to your APT source configuration (assuming you are using main and contrib):

deb http://deb.debian.org/debian buster main contrib

After adding your new sources, disable the previously existing deb lines by placing a hash sign (#) in front of them.

However, if you get better results using a specific mirror that is close to you in network terms, this option is still available.

Debian mirror addresses can be found at https://www.debian.org/distrib/ftplist (look at the list of Debian mirrors section).

For example, suppose your closest Debian mirror is http://mirrors.kernel.org. If you inspect that mirror with a web browser, you will notice that the main directories are organized like this:

      http://mirrors.kernel.org/debian/dists/buster/main/binary-mips/...
      http://mirrors.kernel.org/debian/dists/buster/contrib/binary-mips/...
    

To configure APT to use a given mirror, add a line like this (again, assuming you are using main and contrib):

deb http://mirrors.kernel.org/debian buster main contrib

Note that the dists is added implicitly, and the arguments after the release name are used to expand the path into multiple directories.

Again, after adding your new sources, disable the previously existing archive entries.

4.3.2. Adding APT sources for a local mirror

Instead of using remote package mirrors, you may wish to modify the APT source-list files to use a mirror on a local disk (possibly mounted over NFS).

For example, your package mirror may be under /var/local/debian/, and have main directories like this:

      /var/local/debian/dists/buster/main/binary-mips/...
      /var/local/debian/dists/buster/contrib/binary-mips/...
    

To use this with apt, add this line to your sources.list file:

deb file:/var/local/debian buster main contrib

Note that the dists is added implicitly, and the arguments after the release name are used to expand the path into multiple directories.

After adding your new sources, disable the previously existing archive entries in the APT source-list files by placing a hash sign (#) in front of them.

4.3.3. Adding APT sources from optical media

If you want to use only DVDs (or CDs or Blu-ray Discs), comment out the existing entries in all the APT source-list files by placing a hash sign (#) in front of them.

Make sure there is a line in /etc/fstab that enables mounting your CD-ROM drive at the /media/cdrom mount point. For example, if /dev/sr0 is your CD-ROM drive, /etc/fstab should contain a line like:

      /dev/sr0 /media/cdrom auto noauto,ro 0 0
    

Note that there must be no spaces between the words noauto,ro in the fourth field.

To verify it works, insert a CD and try running

# mount /media/cdrom    # this will mount the CD to the mount point
# ls -alF /media/cdrom  # this should show the CD's root directory
# umount /media/cdrom   # this will unmount the CD
    

Next, run:

# apt-cdrom add
    

for each Debian Binary CD-ROM you have, to add the data about each CD to APT's database.

4.4. Upgrading packages

The recommended way to upgrade from previous Debian releases is to use the package management tool apt.

[Note]Note

apt is meant for interactive use, and should not be used in scripts. In scripts one should use apt-get, which has a stable output better suitable for parsing.

Don't forget to mount all needed partitions (notably the root and /usr partitions) read-write, with a command like:

# mount -o remount,rw /mountpoint
  

Next you should double-check that the APT source entries (in /etc/apt/sources.list and files under /etc/apt/sources.list.d/) refer either to buster or to stable. There should not be any sources entries pointing to stretch.

[Note]Note

Source lines for a CD-ROM might sometimes refer to unstable; although this may be confusing, you should not change it.

4.4.1. Recording the session

It is strongly recommended that you use the /usr/bin/script program to record a transcript of the upgrade session. Then if a problem occurs, you will have a log of what happened, and if needed, can provide exact information in a bug report. To start the recording, type:

# script -t 2>~/upgrade-busterstep.time -a ~/upgrade-busterstep.script
    

or similar. If you have to rerun the typescript (e.g. if you have to reboot the system) use different step values to indicate which step of the upgrade you are logging. Do not put the typescript file in a temporary directory such as /tmp or /var/tmp (files in those directories may be deleted during the upgrade or during any restart).

The typescript will also allow you to review information that has scrolled off-screen. If you are at the system's console, just switch to VT2 (using Alt+F2) and, after logging in, use less -R ~root/upgrade-buster.script to view the file.

After you have completed the upgrade, you can stop script by typing exit at the prompt.

apt will also log the changed package states in /var/log/apt/history.log and the terminal output in /var/log/apt/term.log. dpkg will, in addition, log all package state changes in /var/log/dpkg.log. If you use aptitude, it will also log state changes in /var/log/aptitude.

If you have used the -t switch for script you can use the scriptreplay program to replay the whole session:

# scriptreplay ~/upgrade-busterstep.time ~/upgrade-busterstep.script
    

4.4.2. Updating the package list

First the list of available packages for the new release needs to be fetched. This is done by executing:

# apt update
    
[Note]Note

Users of apt-secure may find issues when using aptitude or apt-get. For apt-get, you can use apt-get update --allow-releaseinfo-change.

4.4.3. Make sure you have sufficient space for the upgrade

You have to make sure before upgrading your system that you will have sufficient hard disk space when you start the full system upgrade described in Section 4.4.5, “Upgrading the system”. First, any package needed for installation that is fetched from the network is stored in /var/cache/apt/archives (and the partial/ subdirectory, during download), so you must make sure you have enough space on the file system partition that holds /var/ to temporarily download the packages that will be installed in your system. After the download, you will probably need more space in other file system partitions in order to both install upgraded packages (which might contain bigger binaries or more data) and new packages that will be pulled in for the upgrade. If your system does not have sufficient space you might end up with an incomplete upgrade that is difficult to recover from.

apt can show you detailed information about the disk space needed for the installation. Before executing the upgrade, you can see this estimate by running:

# apt -o APT::Get::Trivial-Only=true full-upgrade
[ ... ]
XXX upgraded, XXX newly installed, XXX to remove and XXX not upgraded.
Need to get xx.xMB of archives. 
After this operation, AAAMB of additional disk space will be used.
    
[Note]Note

Running this command at the beginning of the upgrade process may give an error, for the reasons described in the next sections. In that case you will need to wait until you've done the minimal system upgrade as in Section 4.4.4, “Minimal system upgrade” before running this command to estimate the disk space.

If you do not have enough space for the upgrade, apt will warn you with a message like this:

E: You don't have enough free space in /var/cache/apt/archives/.
    

In this situation, make sure you free up space beforehand. You can:

  • Remove packages that have been previously downloaded for installation (at /var/cache/apt/archives). Cleaning up the package cache by running apt clean will remove all previously downloaded package files.

  • Remove forgotten packages. If you have used aptitude or apt to manually install packages in stretch it will have kept track of those packages you manually installed, and will be able to mark as redundant those packages pulled in by dependencies alone which are no longer needed due to a package being removed. They will not mark for removal packages that you manually installed. To remove automatically installed packages that are no longer used, run:

    # apt autoremove
            

    You can also use deborphan, debfoster, or cruft to find redundant packages. Do not blindly remove the packages these tools present, especially if you are using aggressive non-default options that are prone to false positives. It is highly recommended that you manually review the packages suggested for removal (i.e. their contents, sizes, and descriptions) before you remove them.

  • Remove packages that take up too much space and are not currently needed (you can always reinstall them after the upgrade). If you have popularity-contest installed, you can use popcon-largest-unused to list the packages you do not use that occupy the most space. You can find the packages that just take up the most disk space with dpigs (available in the debian-goodies package) or with wajig (running wajig size). They can also be found with aptitude. Start aptitude in full-terminal mode, select ViewsNew Flat Package List, press l and enter ~i, then press S and enter ~installsize. This will give you a handy list to work with.

  • Remove translations and localization files from the system if they are not needed. You can install the localepurge package and configure it so that only a few selected locales are kept in the system. This will reduce the disk space consumed at /usr/share/locale.

  • Temporarily move to another system, or permanently remove, system logs residing under /var/log/.

  • Use a temporary /var/cache/apt/archives: You can use a temporary cache directory from another filesystem (USB storage device, temporary hard disk, filesystem already in use, ...).

    [Note]Note

    Do not use an NFS mount as the network connection could be interrupted during the upgrade.

    For example, if you have a USB drive mounted on /media/usbkey:

    1. remove the packages that have been previously downloaded for installation:

      # apt clean
                      

    2. copy the directory /var/cache/apt/archives to the USB drive:

      # cp -ax /var/cache/apt/archives /media/usbkey/
                      

    3. mount the temporary cache directory on the current one:

      # mount --bind /media/usbkey/archives /var/cache/apt/archives
                      

    4. after the upgrade, restore the original /var/cache/apt/archives directory:

      # umount /media/usbkey/archives
                      

    5. remove the remaining /media/usbkey/archives.

    You can create the temporary cache directory on whatever filesystem is mounted on your system.

  • Do a minimal upgrade of the system (see Section 4.4.4, “Minimal system upgrade”) or partial upgrades of the system followed by a full upgrade. This will make it possible to upgrade the system partially, and allow you to clean the package cache before the full upgrade.

Note that in order to safely remove packages, it is advisable to switch your APT source-list files back to stretch as described in Section A.2, “Checking your APT source-list files”.

4.4.4. Minimal system upgrade

In some cases, doing the full upgrade (as described below) directly might remove large numbers of packages that you will want to keep. We therefore recommend a two-part upgrade process: first a minimal upgrade to overcome these conflicts, then a full upgrade as described in Section 4.4.5, “Upgrading the system”.

To do this, first run:

# apt-get upgrade
    

This has the effect of upgrading those packages which can be upgraded without requiring any other packages to be removed or installed.

The minimal system upgrade can also be useful when the system is tight on space and a full upgrade cannot be run due to space constraints.

If the apt-listchanges package is installed, it will (in its default configuration) show important information about upgraded packages in a pager after downloading the packages. Press q after reading to exit the pager and continue the upgrade.

4.4.5. Upgrading the system

Once you have taken the previous steps, you are now ready to continue with the main part of the upgrade. Execute:

# apt full-upgrade
    

This will perform a complete upgrade of the system, installing the newest available versions of all packages, and resolving all possible dependency changes between packages in different releases. If necessary, it will install some new packages (usually new library versions, or renamed packages), and remove any conflicting obsoleted packages.

When upgrading from a set of CDs/DVDs/BDs, you will probably be asked to insert specific discs at several points during the upgrade. You might have to insert the same disc multiple times; this is due to inter-related packages that have been spread out over the discs.

New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version (displayed as held back). This can be resolved by either using aptitude to choose these packages for installation or by trying apt install package.

4.5. Possible issues during upgrade

The following sections describe known issues that might appear during an upgrade to buster.

4.5.1. Dist-upgrade fails with Could not perform immediate configuration

In some cases the apt full-upgrade step can fail after downloading packages with:

E: Could not perform immediate configuration on 'package'.  Please see man 5 apt.conf under APT::Immediate-Configure for details.
      

If that happens, running apt full-upgrade -o APT::Immediate-Configure=0 instead should allow the upgrade to proceed.

Another possible workaround for this problem is to temporarily add both stretch and buster sources to your APT source-list files and run apt update.

4.5.2. Expected removals

The upgrade process to buster might ask for the removal of packages on the system. The precise list of packages will vary depending on the set of packages that you have installed. These release notes give general advice on these removals, but if in doubt, it is recommended that you examine the package removals proposed by each method before proceeding. For more information about packages obsoleted in buster, see Section 4.8, “Obsolete packages”.

4.5.3. Conflicts or Pre-Depends loops

Sometimes it's necessary to enable the APT::Force-LoopBreak option in APT to be able to temporarily remove an essential package due to a Conflicts/Pre-Depends loop. apt will alert you of this and abort the upgrade. You can work around this by specifying the option -o APT::Force-LoopBreak=1 on the apt command line.

It is possible that a system's dependency structure can be so corrupt as to require manual intervention. Usually this means using apt or

# dpkg --remove package_name
    

to eliminate some of the offending packages, or

# apt -f install
# dpkg --configure --pending
    

In extreme cases you might have to force re-installation with a command like

# dpkg --install /path/to/package_name.deb
    

4.5.4. File conflicts

File conflicts should not occur if you upgrade from a pure stretch system, but can occur if you have unofficial backports installed. A file conflict will result in an error like:

Unpacking <package-foo> (from <package-foo-file>) ...
dpkg: error processing <package-foo> (--install):
trying to overwrite `<some-file-name>',
which is also in package <package-bar>
dpkg-deb: subprocess paste killed by signal (Broken pipe)
Errors were encountered while processing:
<package-foo>
    

You can try to solve a file conflict by forcibly removing the package mentioned on the last line of the error message:

# dpkg -r --force-depends package_name
    

After fixing things up, you should be able to resume the upgrade by repeating the previously described apt commands.

4.5.5. Configuration changes

During the upgrade, you will be asked questions regarding the configuration or re-configuration of several packages. When you are asked if any file in the /etc/init.d directory, or the /etc/manpath.config file should be replaced by the package maintainer's version, it's usually necessary to answer yes to ensure system consistency. You can always revert to the old versions, since they will be saved with a .dpkg-old extension.

If you're not sure what to do, write down the name of the package or file and sort things out at a later time. You can search in the typescript file to review the information that was on the screen during the upgrade.

4.5.6. Change of session to console

If you are running the upgrade using the system's local console you might find that at some points during the upgrade the console is shifted over to a different view and you lose visibility of the upgrade process. For example, this may happen in systems with a graphical interface when the display manager is restarted.

To recover the console where the upgrade was running you will have to use Ctrl+Alt+F1 (if in the graphical startup screen) or Alt+F1 (if in the local text-mode console) to switch back to the virtual terminal 1. Replace F1 with the function key with the same number as the virtual terminal the upgrade was running in. You can also use Alt+Left Arrow or Alt+Right Arrow to switch between the different text-mode terminals.

4.6. Upgrading your kernel and related packages

This section explains how to upgrade your kernel and identifies potential issues related to this upgrade. You can either install one of the linux-image-* packages provided by Debian, or compile a customized kernel from source.

Note that a lot of information in this section is based on the assumption that you will be using one of the modular Debian kernels, together with initramfs-tools and udev. If you choose to use a custom kernel that does not require an initrd or if you use a different initrd generator, some of the information may not be relevant for you.

4.6.1. Installing a kernel metapackage

When you full-upgrade from stretch to buster, it is strongly recommended that you install a linux-image-* metapackage, if you have not done so before. These metapackages will automatically pull in a newer version of the kernel during upgrades. You can verify whether you have one installed by running:

# dpkg -l "linux-image*" | grep ^ii | grep -i meta
    

If you do not see any output, then you will either need to install a new linux-image package by hand or install a linux-image metapackage. To see a list of available linux-image metapackages, run:

# apt-cache search linux-image- | grep -i meta | grep -v transition
    

If you are unsure about which package to select, run uname -r and look for a package with a similar name. For example, if you see 4.9.0-8-amd64, it is recommended that you install linux-image-amd64. You may also use apt to see a long description of each package in order to help choose the best one available. For example:

# apt show linux-image-amd64
    

You should then use apt install to install it. Once this new kernel is installed you should reboot at the next available opportunity to get the benefits provided by the new kernel version. However, please have a look at Section 5.1.11, “Things to do post upgrade before rebooting” before performing the first reboot after the upgrade.

For the more adventurous there is an easy way to compile your own custom kernel on Debian. Install the kernel sources, provided in the linux-source package. You can make use of the deb-pkg target available in the sources' makefile for building a binary package. More information can be found in the Debian Linux Kernel Handbook, which can also be found as the debian-kernel-handbook package.

If possible, it is to your advantage to upgrade the kernel package separately from the main full-upgrade to reduce the chances of a temporarily non-bootable system. Note that this should only be done after the minimal upgrade process described in Section 4.4.4, “Minimal system upgrade”.

4.7. Preparing for the next release

After the upgrade there are several things you can do to prepare for the next release.

4.7.1. Purging removed packages

It is generally advisable to purge removed packages. This is especially true if these have been removed in an earlier release upgrade (e.g. from the upgrade to stretch) or they were provided by third-party vendors. In particular, old init.d scripts have been known to cause issues.

[Caution]Caution

Purging a package will generally also purge its log files, so you might want to back them up first.

The following command displays a list of all removed packages that may have configuration files left on the system (if any):

# dpkg -l | awk '/^rc/ { print $2 }'
    

The packages can be removed by using apt purge. Assuming you want to purge all of them in one go, you can use the following command:

# apt purge $(dpkg -l | awk '/^rc/ { print $2 }')
    

If you use aptitude, you can also use the following alternative to the commands above:

# aptitude search '~c'
# aptitude purge '~c'
    

4.8. Obsolete packages

Introducing lots of new packages, buster also retires and omits quite a few old packages that were in stretch. It provides no upgrade path for these obsolete packages. While nothing prevents you from continuing to use an obsolete package where desired, the Debian project will usually discontinue security support for it a year after buster's release[5], and will not normally provide other support in the meantime. Replacing them with available alternatives, if any, is recommended.

There are many reasons why packages might have been removed from the distribution: they are no longer maintained upstream; there is no longer a Debian Developer interested in maintaining the packages; the functionality they provide has been superseded by different software (or a new version); or they are no longer considered suitable for buster due to bugs in them. In the latter case, packages might still be present in the unstable distribution.

Some package management front-ends provide easy ways of finding installed packages that are no longer available from any known repository. The aptitude textual user interface lists them in the category Obsolete and Locally Created Packages, and they can be listed and purged from the commandline with:

# aptitude search '~o'
# aptitude purge '~o'
  

The Debian Bug Tracking System often provides additional information on why the package was removed. You should review both the archived bug reports for the package itself and the archived bug reports for the ftp.debian.org pseudo-package.

For a list of obsolete packages for Buster, please refer to Section 5.1.9, “Noteworthy obsolete packages”.

4.8.1. Transitional dummy packages

Some packages from stretch may have been replaced in buster by transitional dummy packages, which are empty placeholders designed to simplify upgrades. If for instance an application that was formerly a single package has been split into several, a transitional package may be provided with the same name as the old package and with appropriate dependencies to cause the new ones to be installed. After this has happened the redundant dummy package can be safely removed.

The package descriptions for transitional dummy packages usually indicate their purpose. However, they are not uniform; in particular, some dummy packages are designed to be kept installed, in order to pull in a full software suite, or track the current latest version of some program. You might also find deborphan with the --guess-* options (e.g. --guess-dummy) useful to detect transitional dummy packages on your system.



[1] If the debconf priority is set to a very high level you might prevent configuration prompts, but services that rely on default answers that are not applicable to your system will fail to start.

[2] For example: DNS or DHCP services, especially when there is no redundancy or failover. In the DHCP case end-users might be disconnected from the network if the lease time is lower than the time it takes for the upgrade process to complete.

[3] This feature can be disabled by adding the parameter panic=0 to your boot parameters.

[4] Debian's package management system normally does not allow a package to remove or replace a file owned by another package unless it has been defined to replace that package.

[5] Or for as long as there is not another release in that time frame. Typically only two stable releases are supported at any given time.