我尝试单独安装mongo 2.6，但这导致其他软件包被标记为删除。我最终只是卸载了旧包并重新安装了新包，并在此处包含了该过程以供参考。
下面的一些步骤不起作用，但我已将它们及其结果作为尝试的文档包含在内。我之前已经完成了所有数据库的mongodump，所以有一个备份。
最终结果是，除了admin 数据库恢复之外，目前一切似乎都在“工作”。
01.关闭mongod
mongo
use admin
db.shutdownServer()
来自：http://docs.mongodb.org/manual/tutorial/manage-mongodb-processes/
02. 删除了mongodb-10gen 的“固定包”状态：
echo "mongodb-10gen install" | sudo dpkg --set-selections
来自：https://help.ubuntu.com/community/PinningHowto
03. 然后我尝试安装最新的mongo：
sudo apt-get install -y mongodb-org-shell
来自：http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/
04.shell版本好像更新了：
mongo --version
MongoDB shell version: 2.6.6
05.但后来我无法与mongo联系：
mongo
connecting to: test
2015-01-04T00:08:50.482+1000 warning: Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
2015-01-04T00:08:50.483+1000 Error: couldn't connect to server 127.0.0.1:27017 (127.0.0.1), connection attempt failed at src/mongo/shell/mongo.js:146
exception: connect failed
或mongod:
mongod
The program 'mongod' is currently not installed. You can install it by typing:
sudo apt-get install mongodb-server
06. 我运行以下命令查看 apt-get 安装/删除的历史记录：
less /var/log/apt/history.log
得到：
Start-Date: 2015-01-04 00:02:08
Commandline: apt-get install -y mongodb-org-shell
Install: mongodb-org-shell:amd64 (2.6.6)
Remove: mongodb-10gen:amd64 (2.4.9)
End-Date: 2015-01-04 00:02:21
07. 我跑了：
dpkg --get-selections
看到了：
mongodb-10gen deinstall
我认为“卸载”意味着它被标记为删除。
08. 我决定删除所有mongodb-10gen 包：
sudo apt-get purge mongodb-10gen
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
gir1.2-clutter-gst-2.0 gir1.2-ges-1.0 gstreamer1.0-gnonlin libav-tools
libavdevice53 libavfilter3 libavresample1 libges-1.0-0 libgoocanvas-common
libgoocanvas3 libmlt++3 libmlt-data libmlt6 libqjson0 libquicktime2
libsoprano4 melt python-dateutil python-gst-1.0 python-matplotlib
python-matplotlib-data python-mlt python-pygoocanvas python-pyparsing
python-tz python3-bs4 python3-markdown shared-desktop-ontologies
soprano-daemon wkhtmltopdf
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
mongodb-10gen*
0 to upgrade, 0 to newly install, 1 to remove and 3 not to upgrade.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Y
(Reading database ... 246460 files and directories currently installed.)
Removing mongodb-10gen (2.4.9) ...
Purging configuration files for mongodb-10gen (2.4.9) ...
dpkg: warning: while removing mongodb-10gen, directory '/var/lib/mongodb' not empty so not removed
来自：https://askubuntu.com/a/147177
09.我备份了无法删除的目录，即/var/lib/mongodb：
sudo cp -avr /var/lib/mongodb/ /home/
10. 然后将其删除。
cd /var/lib/
sudo rm -rf mongodb/
11.我搜索了是否还有mongodb-10gen 包：
dpkg --get-selections | grep "mongodb-10gen"
什么也没返回。
12. 我通过 Synaptic 包管理器安装了 2.6.6 版的 mongodb-org。
13.我检查了所有 mongodb 包的版本是否相同：
mongodump --version
mongorestore --version
mongo --version
mongod --version
mongos --version
# all returned 2.6.6
14. 然后我对每个数据库转储做了一个mongorestore，例如：
mongorestore --db dname_01 /path/to/dump/dbname_01/
mongorestore --db dname_02 /path/to/dump/dbname_02/
它似乎对所有数据库都有效，但在 admin 数据库上失败：
assertion: 17415 Cannot restore users with schema version 1 to a system with server version 2.5.4 or greater
users 数据库抛出了一些异常，例如：
Restoring to users.pending_registrations without dropping. Restored data will be inserted without raising errors; check your server log
Restoring to users.roles without dropping. Restored data will be inserted without raising errors; check your server log
Restoring to users.users without dropping. Restored data will be inserted without raising errors; check your server log
15. 我跑了db.upgradeCheckAllDBs()：
mongo
use admin
db.upgradeCheckAllDBs()
Checking database local
Checking collection local.startup_log
Checking collection local.system.indexes
Checking database dname_01
...
Checking database admin
Everything is ready for the upgrade!
true
来自：http://docs.mongodb.org/manual/release-notes/2.6-upgrade/#preparedness