免责声明
本教程在 Debian 7.8 (Wheezy) 中测试通过，但由于服务器 / VPS 的不同，不保证此教程在所有服务器 / VPS 中都能正常运行。
因此，请先做完整的备份或者服务器快照！
准备阶段
我测试的是 ikoula 的 5 欧独立服务器，CPU 是 ATOM 520
root@imlonghao:~# cat /etc/debian_version
7.8
如果你不是 Debian 7.8 的，请参照下文升级到这个版本（部分被省略）
root@imlonghao:~# apt-get update
Hit http://ftp.debian.ikoula.com wheezy Release.gpg
Hit http://ftp.debian.ikoula.com wheezy Release
Hit http://ftp.debian.ikoula.com wheezy/main Sources
Hit http://ftp.debian.ikoula.com wheezy/contrib Sources
Hit http://ftp.debian.ikoula.com wheezy/non-free Sources
Hit http://ftp.debian.ikoula.com wheezy/main amd64 Packages
[...]
Reading package lists... Done
root@imlonghao:~# apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
升级过程会更新我们系统的内核，因此，如果你对内核有要求的话请谨慎！
这是升级前的内核
root@imlonghao:~# uname -a
Linux imlonghao 3.2.0-4-amd64 #1 SMP Debian 3.2.65-1+deb7u2 x86_64 GNU/Linux
这是升级前的 sources.list
root@imlonghao:~# cat /etc/apt/sources.list
deb http://ftp.debian.ikoula.com/debian/ wheezy main contrib non-free
deb-src http://ftp.debian.ikoula.com/debian/ wheezy main contrib non-free
deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free
# wheezy-updates, previously known as 'volatile'
deb http://ftp.fr.debian.org/debian/ wheezy-updates main
deb-src http://ftp.fr.debian.org/debian/ wheezy-updates main
我们需要将 sources.list中的 wheezy 替换为 jessie ，运行下面语句
root@imlonghao:~# sed -i "s/wheezy/jessie/g" /etc/apt/sources.list
root@imlonghao:~# cat /etc/apt/sources.list
deb http://ftp.debian.ikoula.com/debian/ jessie main contrib non-free
deb-src http://ftp.debian.ikoula.com/debian/ jessie main contrib non-free
deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free
# jessie-updates, previously known as 'volatile'
deb http://ftp.fr.debian.org/debian/ jessie-updates main
deb-src http://ftp.fr.debian.org/debian/ jessie-updates main
##开始升级
更新源
root@imlonghao:~# apt-get update
Get:1 http://ftp.debian.ikoula.com jessie Release.gpg [2,390 B]
Get:2 http://ftp.debian.ikoula.com jessie Release [126 kB]
Get:3 http://ftp.debian.ikoula.com jessie/main Sources [7,065 kB]
Get:4 http://security.debian.org jessie/updates Release.gpg [1,571 B]
Get:5 http://security.debian.org jessie/updates Release [61.5 kB]
[...]
Fetched 20.1 MB in 9s (2,208 kB/s)
Reading package lists... Done
开始更新，这里可能会比较耗时，不过我的 Atom 服务器用时也不长。
如果你的服务器丢包严重，建议使用 screen
root@imlonghao:~# apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be REMOVED:
[...]
The following NEW packages will be installed:
[...]
The following packages have been kept back:
[...]
The following packages will be upgraded:
[...]
322 upgraded, 197 newly installed, 3 to remove and 1 not upgraded.
Need to get 221 MB of archives.
After this operation, 387 MB of additional disk space will be used.
Do you want to continue [Y/n]?
更新完后，reboot 重启系统
更新完毕
重启系统后，我们就可以看到我们现在已经成功更新到 Debian8.0 了，而内核也有了升级。
root@imlonghao:~# cat /etc/debian_version
8.0
root@imlonghao:~# uname -a
Linux imlonghao 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt9-3~deb8u1 (2015-04-24) x86_64 GNU/Linux