我见过Apt 想要删除 ubuntu-mate-desktop，但这个不一样。
我使用 MATE 桌面，我的 Ubuntu 是：
$ uname -a
Linux MYPC 4.2.0-36-generic #42~14.04.1-Ubuntu SMP Fri May 13 17:27:22 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/issue
Ubuntu 14.04.4 LTS \n \l
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.4 LTS
Release: 14.04
Codename: trusty
就在今天，我正在考虑进行升级：
$ sudo apt-get update
...
$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
compiz compiz-core compiz-gnome compiz-plugins compiz-plugins-default
libcompizconfig0 libdecoration0 overlay-scrollbar-gtk2:i386
The following packages will be upgraded:
apport apport-gtk libc-bin libc-dev-bin libc6 libc6:i386 libc6-dbg libc6-dev
libc6-i386 libpam-smbpass libsmbclient libwbclient0 multiarch-support
python-samba python3-apport python3-problem-report samba samba-common
samba-common-bin samba-dsdb-modules samba-libs samba-vfs-modules smbclient
23 upgraded, 0 newly installed, 0 to remove and 8 not upgraded.
Need to get 26.4 MB of archives.
After this operation, 33.8 kB of additional disk space will be used.
Do you want to continue? [Y/n] ^C
哦，我想，有些包被保留了，为什么不使用来更新它们呢dist-upgrade？
$ sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be REMOVED:
compiz-mate ubuntu-mate-desktop
The following packages will be upgraded:
apport apport-gtk compiz compiz-core compiz-gnome compiz-plugins
compiz-plugins-default libc-bin libc-dev-bin libc6 libc6:i386 libc6-dbg
libc6-dev libc6-i386 libcompizconfig0 libdecoration0 libpam-smbpass
libsmbclient libwbclient0 multiarch-support python-samba python3-apport
python3-problem-report samba samba-common samba-common-bin
samba-dsdb-modules samba-libs samba-vfs-modules smbclient
30 upgraded, 0 newly installed, 2 to remove and 0 not upgraded.
Need to get 29.7 MB of archives.
After this operation, 3,128 kB disk space will be freed.
Do you want to continue? [Y/n] ^C
B...但是等一下，我知道不是想删除ubuntu-mate-desktop，我正在使用它！那么到底是怎么回事，为什么更新要删除ubuntu-mate-desktop？我应该如何更新，以便保留ubuntu-mate-desktop？
编辑：我放手了dist-upgrade，所以ubuntu-mate-desktop被删除了；幸运的是它只是一个元包，所以重启后我仍然有 MATE 在运行，但现在我得到：
$ sudo apt-get install ubuntu-mate-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
ubuntu-mate-desktop : Depends: compiz-mate but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
为什么，哦，为什么……不能compiz-mate共存compiz-gnome？为什么一定要破坏我的系统？……