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很多同学都是在自己的机器上安装双系统，也就是说用来装linux的空间不会很多。在装的过程中都喜欢把boot挂单独挂分区，一般设置100M，
可随着linux升级，往往会攒下好几个内核，某一天系统会提示你升级失败，空间不足了。。。
更改boot分区大大小不晓得可不可以做到，貌似linux下还没有无损分区的概念。
既然已经知道是boot空间不足了，那首先我们看看里面都有神马东西！！
expired@expired:~$ ls /boot
abi-2.6.35-25-generic memtest86+.bin
abi-2.6.35-27-generic memtest86+_multiboot.bin
abi-2.6.35-28-generic System.map-2.6.35-25-generic
config-2.6.35-25-generic System.map-2.6.35-27-generic
config-2.6.35-27-generic System.map-2.6.35-28-generic
config-2.6.35-28-generic vmcoreinfo-2.6.35-25-generic
grub vmcoreinfo-2.6.35-27-generic
initrd.img-2.6.35-25-generic vmcoreinfo-2.6.35-28-generic
initrd.img-2.6.35-27-generic vmlinuz-2.6.35-25-generic
initrd.img-2.6.35-28-generic vmlinuz-2.6.35-27-generic
lost+found vmlinuz-2.6.35-28-generic
我们可以看到都是一些内核启动文件，很明显有些是我们不需要的，其实以上都还是我已经卸载了俩比较老的内核的情况了，没商量，不需要的就当垃圾处理掉。
首先请用uname -a看下自己当前启动的是哪个内核。
expired@expired:~$ uname -a
Linux expired 2.6.35-28-generic #49-Ubuntu SMP Tue Mar 1 14:39:03 UTC 2011 x86_64 GNU/Linux
从中可以看到我此刻启动的是2.6.35-28-generic，再用dpkg命令看下你的机器上都有哪些内核文件。
expired@expired:~$ dpkg --get-selections |grep linux-image
linux-image-2.6.35-22-generic deinstall
linux-image-2.6.35-24-generic deinstall
linux-image-2.6.35-25-generic install
linux-image-2.6.35-27-generic install
linux-image-2.6.35-28-generic install
linux-image-generic install
不少，理论上除正在用的都可以删除，但刚升级的东西可能不稳定，为保险起见，保留1-2个之前版本吧。
运行apt-get remove命令卸载不需要的内核。
expired@expired:~$ sudo apt-get remove linux-image-2.6.35-25-generic
The following packages will be REMOVED:
linux-image-2.6.35-25-generic
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 139MB disk space will be freed.
Do you want to continue [Y/n]? y
出现以上提示问是否继续，按y或者直接回车继续。完成后会有如下提示：
DKMS: uninstall Completed.
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 2.6.35-25-generic /boot/vmlinuz-2.6.35-25-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 2.6.35-25-generic /boot/vmlinuz-2.6.35-25-generic
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.35-28-generic
Found initrd image: /boot/initrd.img-2.6.35-28-generic
Found linux image: /boot/vmlinuz-2.6.35-27-generic
Found initrd image: /boot/initrd.img-2.6.35-27-generic
Found memtest86+ image: /memtest86+.bin
Found Windows 7 (loader) on /dev/sda1
Found Windows Vista (loader) on /dev/sda4
done
现在的ubuntu会自动重建启动菜单grub.cfg，所以就一步到位了。卸载完后可以用df命令看下boot分区的空间使用情况。
expired@expired:~$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda9 19223252 9429624 8817144 52% /
/dev/sda7 93207 53279 35116 61% /boot
ok，已经腾出35m空间了，现在可以运行sudo apt-get upgrade升级了。
再用dpkg看下还剩什么东西。
expired@expired:~$ dpkg --get-selections | grep linux-image
linux-image-2.6.35-25-generic deinstall
linux-image-2.6.35-27-generic install
linux-image-2.6.35-28-generic install
linux-image-generic install
linux-image-2.6.35-25-generic 显示deinstall，表示已经删除，也许你觉得留着这个也不好看，那就试试下面的命令：
expired@expired:~$sudo dpkg -P linux-image-2.6.35-25-generic
(Reading database ... 286964 files and directories currently installed.)
Removing linux-image-2.6.35-25-generic ...
Purging configuration files for linux-image-2.6.35-25-generic ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 2.6.35-25-generic /boot/vmlinuz-2.6.35-25-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 2.6.35-25-generic /boot/vmlinuz-2.6.35-25-generic
呵呵，其实打一开始就可以用purge这个参数一步到位地卸载，即：expired@expired:~$sudo apt-get purge linux-image-3.2.0-26-generic
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
linux-image-3.2.0-26-generic*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 0 B of additional disk space will be used.
Do you want to continue [Y/n]? y
(Reading database ... 286964 files and directories currently installed.)
Removing linux-image-3.2.0-26-generic ...
Purging configuration files for linux-image-3.2.0-26-generic ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.2.0-26-generic /boot/vmlinuz-3.2.0-26-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 3.2.0-26-generic /boot/vmlinuz-3.2.0-26-generic
因为之前已经remove过了，所以只留下个配置在数据库记录中，再purge时无空间释放。
0 B of additional disk space will be used
再次看下运行后的结果expired@expired:~$ dpkg --get-selections | grep linux-image
linux-image-3.2.0-32-generic install
linux-image-generic install
expired@expired:~$ dpkg -l | grep linux-image
ii linux-image-3.2.0-32-generic 3.2.0-32.51 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
ii linux-image-generic 3.2.0.32.35 Generic Linux kernel image
ok，刚才的残留已经删除了。