在升级系统前，强烈建议您进行一次完整的备份，或者至少备份您不愿意丢失的数据和配置信息。升级工具和流程是非常可靠的，但升级过程中的硬件错误会对您的系统造成严重损害。

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.

升级过程本身不会修改 /home 下的任何内容。但某些程序(比如部分 Mozilla 套件，以及 GNOME 和 KDE 桌面环境)会在新版本的程序第一次启动时用新的默认值来覆盖现有的用户设置。做为一种预防措施，您也许想备份用户目录下的隐藏文件和目录(“dotfiles”)。该备份有助于您恢复或者重建原有设置。另外，您可能还需要把该事项通知给用户。

任何软件包安装操作都必须以超级用户权限执行，您可以以 root 身份登录，或使用 su 或者 sudo 来获取必要的访问权限。

升级需要几个前提条件，您应当在实际升级前检查它们。

提前通知所有用户您正在计划的任何升级将是明智的决定，但是通过 ssh 连接访问您系统的用户可能在升级过程中不会注意到什么东西，而且应该可以继续正常工作。

如果您希望采取更多的预防措施，请在升级前备份或者卸载 /home 分区。

You will have to do a kernel upgrade when upgrading to squeeze, so a reboot will be necessary.

During the upgrade process, there might be services associated with packages that will be include in the upgrade. If this is the case, these services might be stopped while the packages that are going to be upgraded are being replaced and configured. During this time, these services will not be available.

The precise downtime for these service will vary depending on the number of packages being upgraded in the system, and it also includes the time the system administrator answers the configuration questions from different package upgrades (if any). Notice that if the upgrade process is left unattended and the system requests input throughout the upgrade there is a high possibility of services being unavailable^[4] for a significant period of time.

If the system being upgraded provides critical services for your users or network^[5], you can reduce the downtime if you do a minimal system upgrade, as described in 第 4.4.4 节 “最小系统升级”, followed by a kernel upgrade and reboot (see 第 4.4.5 节 “Upgrading the kernel and udev”), and then upgrade the packages associated with your critical services. Upgrade these packages prior to doing the full upgrade described in 第 4.4.6 节 “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.

由于 lenny 和 squeeze 的内核在驱动、硬件探测与命名以及设备文件的命名和排序等方面有着诸多变化，在更新后您可能会在重启系统时遇到很大的问题。本章和发行注记的下一章记录了很多已知的潜在问题。

由于这个原因，当您的系统重启失败(或对于远程管理系统来说，无法从网络唤醒)时，请确保您能够将其恢复。

如果您通过 ssh 远程连接进行升级，则强烈建议您采取必要的预防措施以便通过远程串行终端来访问该服务器。因为在升级内核并重启后，某些设备可能会被改名(如在第 4.6.2 节 “设备枚举的顺序”中所描述的情况)，而您将不得不通过本地控制台修复系统配置。还有，如果系统在升级过程中意外重启您可能需要使用本地控制台进行修复。

很明显首先应尝试的就是以您原来的内核重启。然而，由于本文档其它地方所描述的各种各样的问题，并不保证可以成功重启。

如果重启失败了，您需要采取替代方案来启动您的系统以便访问和修复它。其中一种选择是使用特制的急救盘或者 Linux live CD。以这些介质引导后，您应该可以挂载您的根文件系统并 chroot 到它里面来检查并修复问题。

我们推荐的另一种选择是使用 squeeze Debian 安装程序的拯救模式。使用安装程序的优点是，您可以从众多安装方式中选择最适合您情况的一种。更多信息请查询安装手册第 8 章的“修复损坏的系统”一节以及 Debian 安装程序常见问题。

发行版升级应该从本机的文本模式虚拟控制台(或者直连串行终端)，或者通过 ssh 远程连接进行。

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

为了在远程升级时获得额外的可靠性保障，我们建议您在由 screen 程序生成的虚拟控制台中执行升级过程。它能进行可靠的重新连接并确保，即使远程连接失败，升级过程也不会被打断。

	重要
	您不应该在您要升级的机器上使用 telnet、rlogin、rsh 之类的东西，或者从 xdm、gdm、kdm 之类管理的 X 会话中升级。因为那些服务中的任意一个在升级中都有可能被中止，进而导致出现一个不可访问的，只升级了一半的系统。

Due to bug #512951, the splashy package needs to be purged prior to the upgrade.

	# apt-get purge splashy

在某些情况下，使用 apt-get 代替 aptitude 安装软件包时，可能会让 aptitude 认为包“未被使用”，并安排它被移除。一般来说，在正式升级前您应该确保系统是最新且“干净的”。

有鉴于此，您应该复查包管理器 aptitude 中是否有未决操作。如果包管理器中有软件包被安排为移除或更新，那么这可能对升级过程有负面影响。注意，要更正这一错误只可能是，您的 sources.list 仍然指向 lenny 而非 stable 或是 squeeze。参看第 A.2 节 “检查您的 sources list”。

要执行复查的话，您必须以“图形模式”运行 aptitude 并按下 g (“Go”)。如果显示有任何未决操作，您都应该复查它们，然后要么修复，要么执行建议的操作。如果没有建议的操作，会有一条信息 “没有软件包需要安装、删除或者升级”出现。

如果已经设置 APT 从一个非 stable(如 testing)版安装特定软件包，您可能必须改变 APT pinning 设置(保存在 /etc/apt/preferences 中)以允许升级至新的 stable 版中的包。更多有关 APT pinning 的信息可以在 apt_preferences(5) 中找到。

不管用什么方法升级，我们都建议您先检查所有软件包的状态，并验证所有包都处于可升级状态。以下命令会显示任何半安装或是配置失败的包，还有那些有任何错误状态的包。

# dpkg --audit

您也可以用 dselect、aptitude 来审查系统中的所有包的状态，也可以用如下的命令来审查

# dpkg -l | pager

或是

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

在升级前移除所有的 hold 状态是很有必要的。如果有任何对升级而言有重大影响的包处于 hold 状态，升级会失败。

注意 aptitude 使用一种与 apt-get 及 dselect 不同的方法来注册 hold 状态的包。您可以用以下命令来确认 aptitude 中处于 hold 状态的包。

# aptitude search "~ahold" | grep "^.h"

如果您想检查 apt-get 中哪些包设置了 hold 状态，可以用

# dpkg --get-selections | grep hold

如果您在本地更改并重新编译了一个包，且并未重命名，或是在版本号中放入新的纪元号，您就必须将它设为 hold 状态，以防止它被升级。

The “hold” package state for apt-get can be changed using:

# echo package_name hold | dpkg --set-selections

Replace hold with install to unset the “hold” state.

如果有任何需要修复的东西，您最好确保 sources.list 仍然指向 lenny ，就像第 A.2 节 “检查您的 sources list”中所说的那样。

如果您已经把 proposed-updates 区加入您的 /etc/apt/sources.list 文件，那么您应当在升级前移除它，这样可以降低冲突发生的概率。

如果有任何非 Debian 的软件包安装在您的系统中，您应该意识到它们可能会在升级期间因为依赖性冲突而被移除。如果这些包是通过在 /etc/apt/source.list 中添加一个额外的软件源而安装的，您应该检查那个软件源是否也提供 squeeze 下编译好的包，并同时像您的 Debian 软件源那样更改相应的源。

某些用户可能有非官方的 backported “较新的” 包版本存在于他们安装的 Debian lenny 系统中。升级期间那样的包是最可能引起问题的，因为它们可能会导致文件冲突^[7]。第 4.5 节 “升级期间可能遇到的问题”已经有一些关于如何处理将会出现的文件冲突的信息了。

默认配置用于从主 Debian 网络服务器上安装，但您可能希望修改 /etc/apt/sources.list 以使用其它的镜像，离您最近的网络镜像是一种更好的选择。

Debian HTTP 或 FTP 镜像地址能在 http://www.debian.org/distrib/ftplist 找到(参看“ Debian 镜像列表”一节)。HTTP 镜像通常比 FTP 镜像快。

例如，假设离您最近的 Debian 镜像是 http://mirrors.kernel.org。当用网络浏览器或是 FTP 程序检查那个镜像时，您会注意到主目录被组织成了如下情况：

http://mirrors.kernel.org/debian/dists/squeeze/main/binary-i386/...
http://mirrors.kernel.org/debian/dists/squeeze/contrib/binary-i386/...

要让 apt 使用这个镜像，您将此行添加至 sources.list 文件：

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

注意明显加上去的‘dists’，这个发行版名字后的参数用于将路径扩展成多个目录。

添加新源后，在 sources.list 中通过在以前存在的 “deb” 行前加上一个井号(#)来禁用它们。

您可能希望通过修改 /etc/apt/sources.list 来使用一个本地磁盘上的镜像(也许是通过 NFS 挂载的)，来代替 HTTP 或 FTP 软件源镜像。

例如，假设您的镜像位于 /var/ftp/devian/ 下，并且有如下的主目录：

/var/ftp/debian/dists/squeeze/main/binary-i386/...
/var/ftp/debian/dists/squeeze/contrib/binary-i386/...

要让 apt 使用它，需要把这一行添加至 sources.list 文件：

deb file:/var/ftp/debian squeeze main contrib

注意明显加上去的‘dists’，这个发行版名字后的参数用于将路径扩展成多个目录。

添加新源后，在 sources.list 中通过在以前存在的 “deb” 行前加上一个井号(#)来禁用它们。

如果您只想用 CD 安装，在 /etc/apt/sources.list 中的 “deb” 行前放上井号(#)注释掉它们。

确保在 /etc/fstab 中有一行允许您挂载 CD-ROM 于 /cdrom 挂载点(apt-cdrom 必须指定挂载点为 /cdrom )。例如，假设 /dev/hdc 就是您的 CD-ROM，/etc/fstab 中应该带有一行：

/dev/hdc /cdrom auto defaults,noauto,ro 0 0

注意在第四段 defaults,noauto,ro 之间必须无空格。

要验证设置是否有效，插入一片 CD，尝试运行

# mount /cdrom    # 挂载 CD 至挂载点
# ls -alF /cdrom  # 显示 CD 的根目录
# umount /cdrom   # 卸载 CD

下一步，运行：

# apt-cdrom add

每片您所拥有的 Debian 二进制 CD-ROM 都要这么做，以便将每片 CD 的数据添加至 APT 的数据库。

强烈推荐您使用 /usr/bin/script 程序来记录升级会话中的交互信息。这样如果有问题了，您就有一份问题报告。而且需要的话，您也可以在错误报告中提供额外信息。要开始记录，输入：

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

或是类似命令。不要将输出文件放在临时目录下，如 /tmp 或 /var/tmp (这些目录下的文件可能会在升级或重启时被删除)

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-squeeze.script to view the file.

在完成升级后，您可以在提示符下输入 exit 停止 script。

如果已经对 script 使用了 -t 选项，您就可以用 scriptplay 程序来回放整个过程：

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

首先，需要获取新发行版的可用包列表。执行：

# apt-get update

You have to make sure before upgrading your system that you have sufficient hard disk space when you start the full system upgrade described in 第 4.4.6 节 “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 might be difficult to recover from.

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

# apt-get -o APT::Get::Trivial-Only=true dist-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.

	注意
	由于下一节将要谈到的问题，在即将开始更新前执行这条命令可能会给出一个错误。如果那样的话，您需要等至已经如第 4.4.4 节 “最小系统升级”所述的那样做过最小系统升级并且升级过内核，这样您才可以运行这条命令来预估所需的磁盘空间。

If you do not have enough space for the upgrade, apt-get 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:

注意为了安全地移除软件包，建议您换回 lenny 的 sources.list，就像第 A.2 节 “检查您的 sources list”中描述的那样。

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 第 4.4.6 节 “Upgrading the system”.

To do this first, run:

# apt-get upgrade

这会升级那些不需要删除或安装其它任何包的软件。

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 constrains.

The udev version in squeeze requires a kernel of version 2.6.26 or newer with the CONFIG_SYSFS_DEPRECATED option disabled and the CONFIG_INOTIFY_USER and CONFIG_SIGNALFD options enabled. Because the standard Debian kernels in lenny (version 2.6.26) have CONFIG_SYSFS_DEPRECATED enabled, and the udev version in lenny will not provide all the functionality expected by the latest kernels, special care must be taken when upgrading to avoid putting your system in an unbootable state.

Booting the 2.6.26 kernel from lenny with the udev from squeeze may result in a failure to correctly assign names to network devices, and will also fail to apply certain additional permissions to block devices (such as access by the disk group). The software itself will appear to be working, but some rules (for example, network-based rules) will not be loaded properly. It is therefore strongly recommended that you upgrade the kernel on its own at this point, to ensure a compatible kernel is available before upgrading udev.

要进行此次内核升级，执行：

# apt-get install linux-image-2.6-flavor

参看第 4.6.1 节 “安装内核元数据包”来帮助您决定应该安装哪个修订号的内核包。

Users of the grub bootloader should make sure that update-grub is run as part of the kernel upgrade, or run it manually.

Immediately after upgrading the kernel, you should also install the new udev to minimize the risk of other incompatibilities caused by using the old udev with a new kernel ^[8]. You can do this by running:

# apt-get install udev

Once you have upgraded both the kernel and udev the system should be rebooted.

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

# apt-get dist-upgrade

	注意
	The upgrade process for other releases recommended the use of aptitude for the upgrade. This tool is not recommended for upgrades from lenny to squeeze.

这将对系统进行一次全面的升级，比如：安装所有包的最新可用版本，解决不同发行版的包之间所有潜在的依赖性变动。如有必要，它会安装一些新包(通常是新库，或是重命名的包)，并删除任何有冲突的过时包。

当从一套 CD-ROM (或 DVD)升级时，您会在升级期间的某几个地方被要求插入指定的 CD 盘片。您可能不得不多次插入相同的盘片，这是因为互相依赖的包已经被分散到整个 CD 套件中去了。

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-get -f install package.

Support for cryptoloop has been dropped from the Linux kernel packages included in Debian 6.0. Existing installations using cryptoloop need to be transitioned to dm-crypt before the upgrade.

The upgrade process to squeeze might ask for removal of packages in 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.

Some common packages that are expected to be removed include: autofs (replaced by autofs5), dhcp3 (replaced by isc-dhcp), madwifi-source, python-setuptools and python2.4 (replaced by python2.6). For more information about packages obsoleted in squeeze, see 第 4.10 节 “过时的包”.

如果使用 aptitude, apt-get 或 dpkg 操作时出现错误

E: Dynamic MMap ran out of room

默认的缓存区空间不足。您可以通过删除或注释掉 /etc/apt/sources.list 中不需要的行，或通过增加缓存大小来解决这个问题。缓存大小能通过在 /etc/apt/apt.conf 中设置 APT::Cache-Limit 来增加。下面的命令会为它设置一个足够升级值：

# echo 'APT::Cache-Limit "12500000";' >> /etc/apt/apt.conf

这里假设您还未在那个文件中对该变量进行过设置。

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-get 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-get 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-get or

# dpkg --remove package_name

来消除某些引起问题的包，或是

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

在极端情况下，您可能不得不像以下命令一样强制重新安装某个包

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

如果您从“纯粹的” lenny 系统升级就不会出现文件冲突，但如果您装有非官方的 backport 包就可能出现冲突。文件冲突会导致类似以下这样的错误：

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>

您可以尝试用错误信息中的最后一行提示，强制删除包来解决文件冲突：

# dpkg -r --force-depends package_name

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

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.

如果您不确定该做什么，那就记下包或文件的名称，并稍后排出它们的顺序。您可以通过在 script 命令记录的输出文件中搜索来查看升级期间显示在屏幕上的信息。

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 will happen in desktop systems when gdm is restarted.

To recover the console where the upgrade was running you will have to use Ctrl+Alt+F1 to switch back to the virtual terminal 1 if in the graphical startup screen or use Alt+F1 if in the local text-mode console. Replace F1 with the function key with the same number of 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.

In most cases, packages should upgrade smoothly between lenny and squeeze. There are a small number of cases where some intervention may be required, either before or during the upgrade; these are detailed below on a per-package basis.

当您从 lenny 全面升级至 squeeze 时，强烈推荐您安装新的 linux-image-2.6-* 元数据包。此包可能由 dist-upgrade 自动安装了。您可以验证此步，执行：

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

如果您没有看到任何输出，那么您需要手工安装一个新的 linux-image 包。要查看可用的 linux-image-2.6 的元数据包列表，执行：

# apt-cache search linux-image-2.6- | 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 '2.6.26-2-686', it is recommended that you install linux-image-2.6-686. You may also use apt-cache to see a long description of each package in order to help choose the best one available. For example:

# apt-cache show linux-image-2.6-686

You should then use apt-get 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.

For the more adventurous there is an easy way to compile your own custom kernel on Debian GNU/Linux. Install the kernel-package tool and read the documentation in /usr/share/doc/kernel-package. Alternatively, you can also use the kernel sources, provided in the linux-source-2.6 package. You can make use of the deb-pkg target available in the sources' makefile for building a binary package. There are some differences in these two approaches, please consult the respective package's documentation.

如果有可能，把内核包的升级从主 dist-upgrade 中独立出来是有利的，这能减少出现一个临时不可引导的系统的机会。注意，这只能在最小升级(参看第 4.4.4 节 “最小系统升级”)结束后才能做。

In lenny and later, a new kernel mechanism for hardware discovery may change the order in which devices are discovered on your system on each boot, affecting the device names assigned to them. For example, if you have two network adapters that are associated with two different drivers, the devices eth0 and eth1 refer to may be swapped.

For network devices, this reordering is normally avoided by the definitions at /etc/udev/rules.d/70-persistent-net.rules for udev. Since these rules were already in place in lenny, no additional action should be required when upgrading to squeeze to get the benefit of stable network device names. Please note, however, that this udev mechanism means that a given network device name is tied to a particular piece of hardware; if you, for instance, exchange ethernet adapters in a deployed squeeze system, the new adapter will get a new interface name instead of using the existing one. To reuse an existing device name for new hardware, you will need to delete the associated entry from /etc/udev/rules.d/70-persistent-net.rules.

For storage devices, you may be able to avoid this reordering by using initramfs-tools and configuring it to load storage device driver modules in the same order they are currently loaded. However, in light of other changes to the storage subsystem of the Linux kernel as described at 第 5.1.1 节 “Migration of disk drivers from IDE to PATA subsystem”, this is usually not worth the effort and it is recommended instead to use device names that are guaranteed to be stable over time, such as the UUID aliases ^[9] in the /dev/disk/by-uuid/ directory or LVM device names in /dev/mapper/.

如果用 initramfs-tools 创建的 initrd 引导系统，在某些情况下由 udev 创建的设备文件可能对于启动脚本的执行来讲太慢了点。

这通常表现为引导失败，由于根文件系统无法挂载，您会进入调试环境。但当您回头检查时，所需的所有设备都存在于 /dev 下。只要根文件系统存在于 USB 磁盘或是 RAID上，尤其是使用了 LILO 时，就会出现这种问题。

解决此问题的方法就是用引导参数 rootdelay=9。这个超时值(秒)可能需要调整一下。

One can avoid this problem entirely by using an identifier for the root filesystem that does not change from one boot to the next. There are two possible methods for doing this - labeling the filesystem, or using the filesystem's universally unique identifier (UUID). These methods are supported in Debian since the etch release.

两种方法各有优缺点。文件系统标签可读性好，但如果您的系统中有另一个同名的文件系统时，就会带来问题。UUID 可读性较差，但极不可能出现两个互相冲突的 UUID。

以下范例中，我们假设根文件系统位于 /dev/hda6，同时再假设您的系统装有运行正常的 udev 和 ext2 或是 ext3 文件系统。

要使用文件系统标签：

要使用 UUID：

During the upgrade, you will normally have been offered the option to "chainload" GRUB 2: that is, to keep GRUB Legacy as the primary boot loader but to add an option to it to load GRUB 2 and then start your Debian GNU/Linux system from that. This allows you to verify that GRUB 2 works on your system before committing to use it permanently.

Once you have confirmed that GRUB 2 works, you should switch to using it properly: the chainloading setup is only intended to be used temporarily. You can do this by running upgrade-from-grub-legacy.

The GRUB Manual has more information on the changes between GRUB Legacy and GRUB 2, some of which may require changes to complex configurations. If you have not modified your boot loader configuration, you should not need to do anything further.

来自 lenny 的某些包在 squeeze 中已经被分为好几个包，通常这是为了改善系统的可维护性。在此情况下，为了能平滑升级，squeeze 通常提供“哑”包(即空包)，它与 lenny 中的旧包名称相同，但有依赖性，促使它们安装新包。这些“哑”包在升级成功后就会被认为是过时的包，且能够被安全地移除。

Most (but not all) dummy packages' descriptions indicate their purpose. Package descriptions for dummy packages are not uniform, however, so you might also find deborphan with the --guess-* options (e.g. --guess-dummy) useful to detect them in your system. Note that some dummy packages are not intended to be removed after an upgrade but are, instead, used to keep track of the current available version of a program over time.