Synopsis of the Problem
You may have heard me mention that I purchased a used rack server a couple years ago to help teach myself Linux server administration. It's an HP DL-380 G3 with dual single core Zeons and 12Gb of RAM. It came with two 75Gb SCSI drives in RAID1, dedicated to the OS. Since the seller wanted more for additional internal SCSI drives, and those old server drives are limited to 120Gb anyway, I plugged in a PCI-X SATA adapter and connected 750Gb drive externally and mounted it as /home. I moved over the 2Gb USB drive I had on my Chumby (as opposed to transferring the files) and it shows up as /media/usb0. I installed Ubuntu server 10.04 (recently updated to 12.04) because CentOS didn't support the RAID controller out of the box and I had frustrated the lack of support for up to date packages on Debian Lenny on the desktop.
With 75Gb dedicated to the OS and application packages, you can imaging my surprise when after a update and upgrade, I had a report that my /boot was full. It was until I look at the output from fdisk that I remembered the Ubuntu installer created a separate partition for /boot. At the risk of oversimplifying the purpose of /boot, it is where your current and past kernel files are stored. Unless the system removes older kernels (most desktop systems seem to) the storage required for /boot will increase with every kernel upgrade.
This is the output of df before culling the kernels
Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/oriac-root 66860688 6593460 56870828 11% / udev 6072216 4 6072212 1% /dev tmpfs 2432376 516 2431860 1% /run none 5120 0 5120 0% /run/lock none 6080936 0 6080936 0% /run/shm cgroup 6080936 0 6080936 0% /sys/fs/cgroup /dev/cciss/c0d0p1 233191 224953 0 100% /boot /dev/sda1 721075720 297668900 386778220 44% /home /dev/sdb1 1921902868 429219096 1395056772 24% /media/usb0
This directory listing shows I had many old kernels in /bootabi-2.6.32-24-generic-pae
The Solution I FoundI ran across some articles that suggested I could use 'uname -r' to identify my current running kernel (3.2.0-31, the -32 apparently kernel ran out of space before it completed installing) and just delete the files with other numbers. That didn't seem prudent, and fortunately I've found what seems to be a more elegant solution on upubuntu.com .
Verify your current running kernel
Linux will often keep older kernels so that you can boot into and older version from Grub (at least on a desktop). Fedora has an environment setting to tell the OS just how many old kernels you want to maintain [installonly_limit in /etc/yum.conf]. Please leave a comment if you know of an analog in Debian/Ubuntu.
List the kernels currently installed on you system.
dpkg --list | grep linux-image
Cull all the kernels but the current oneThe next line is the key, make sure you copy and paste exactly from the shownotes. I'm not much good with regular expressions, but I can see it's trying to match all the packages starting with 'linux-image' but containing a number string different from the one returned by 'uname -r', and remove those packages. Obviously, this specific command will only work with Debian/Ubuntu systems, but you should be able to adapt it to your distro. The '-P' is my contribution, so you can see what packages you are eliminating before the change becomes final.
sudo aptitude -P purge ~ilinux-image-\[0-9\]\(\!`uname -r`\)
Make sure Grub reflects your changesFinally, the author recomends running 'sudo update-grub2' to make sure Grub reflects your current kernel status (the above command sees to do this after every operation anyway, but better safe than sorry.
It's worth noting I still don't have my -32 kernel update, so I'll let you know if the is anything required to get kernel updates get started again.
My df now shows 14% usage in /boot and a directory listing on /boot only shows the current kernel files.
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/oriac-root 66860688 5405996 58058292 9% /
udev 6072216 12 6072204 1% /dev
tmpfs 2432376 516 2431860 1% /run
none 5120 0 5120 0% /run/lock
none 6080936 0 6080936 0% /run/shm
cgroup 6080936 0 6080936 0% /sys/fs/cgroup
/dev/cciss/c0d0p1 233191 29321 191429 14% /boot
/dev/sda1 721075720 297668908 386778212 44% /home
/dev/sdb1 1921902868 429219096 1395056772 24% /media/usb0