Openwrt for x86 - part 2
This section requires knowledge of bash. Please get a professional to help if you are unsure.
These commands find an unused loop device and attach it to the image file.
fdisk is used to manipulate the disk partition table.
To see the existing partitions, type “p” at the fdisk prompt.
Now delete the root partition and create a new one that covers all available space.
Another thing worth noting: kpartx and fdisk use different naming conventions. kpartx uses “/dev/mapper/device_name”, for example ”/dev/mapper/loop3p1″. fdisk uses “/dev/device_name”, such as “/dev/loop3p1″. This is because kpartx works with the device mapper.
Now run “fsck” to check the file system before resizing it. In fact, some file systems can’t be resized until they are checked.
Finally, resize the root file system.
The root partition of the official x86 OpenWrt image is not very big, about 50 MiB. Many find it too small after installing a few add-on packages. Here I will cover the steps to expand it. The resultant image can be used in a live USB (see Easy Live USB for x86 OpenWRT) or copied to a hard disk.
Procedure Outline
All commands below are run in Bash.
- Get an uncompressed disk image.
- Pad image to desired size
- Attach the image file to a loop device
- Edit image partition table to enlarge the root partition
- Resize the file system in root partition
- Detach the image from the loop device.
Uncompress Image File
Use whichever method you like to download an image file from OpenWrt (http://downloads.openwrt.org) and uncompress it using gzip. For example, these two commands download and uncompress the 10.03.1-rc6 disk image.bash$ wget --quiet http://downloads.openwrt.org/backfire/10.03.1-rc6/x86_generic/openwrt-x86-generic-combined-ext2.img.gz bash$ gunzip openwrt-x86-generic-combined-ext2.img.gzAlternative, you can just copy an image file from a live USB flash drive. This will save you the trouble of restoring custom configurations.
Pad Disk Image
The next step is to use “dd” to increase the size of the disk image.bash$ dd if=/dev/zero bs=1M count=50 >> openwrt-x86-generic-combined-ext2.imgThis command appends 50 MiB of zeros to the end of the disk image: “if=/dev/zero” tells dd to copy data from /dev/zero; “bs=1M” sets the block size to 1 MiB (1024*1024 bytes); “count=50” tells dd to copy 50 blocks.
Attach to Loop Device
Note: All commands from this point to the end need to be run by a user with root privilege.These commands find an unused loop device and attach it to the image file.
bash$ loop_dev=`losetup -f` bash$ echo $loop_dev /dev/loop3 bash$ losetup $loop_dev openwrt-x86-generic-combined-ext2.imgThe first command uses “losetup -f” to find an unused device and stores the result in the shell variable loop_dev. The “echo” command shows the device found. Finally “losetup” attaches the device to the disk image.
Edit Partition Table
To expand a disk partition, it needs to be deleted first. A new, larger partition is then created to take its place. This new partition must start from the same sector as the old to prevent loss of data.fdisk is used to manipulate the disk partition table.
bash$ fdisk -u=sectors -c=dos $loop_devThe -u option asks fdisk to list partitions in sectors. The -c option tells fdisk to operate in DOS compatibility mode. $loop_dev is the loop device attached to the image file.
To see the existing partitions, type “p” at the fdisk prompt.
Command (m for help): p
Disk /dev/loop3: 107 MB, 107437568 bytes
16 heads, 63 sectors/track, 208 cylinders, total 209839 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/loop3p1 * 63 9071 4504+ 83 Linux
/dev/loop3p2 9135 107855 49360+ 83 Linux
fdisk shows /dev/loop3 has 209839 sectors. It also lists two partitions. The first one, /dev/loop3p1, is a small boot partition. The second, /dev/loop3p2, is the root partition. The root partition starts from sector 9135. Make a note of this number.Now delete the root partition and create a new one that covers all available space.
Command (m for help): d
Partition number (1-4): 2
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4, default 2): 2
First sector (9072-209838, default 9072): 9135
Last sector, +sectors or +size{K,M,G} (9135-209838, default 209838): 209838
Command (m for help): w
The partition table has been altered!
The “d” command asks fdisk to delete a partition, and “2” selects the
second partition for deletion. The “n” command asks fdisk to create a
new partition. “p” specifies a primary partition, and “2” selects the
second primary partition. The first sector of this partition is sector
9135, same as the deleted partition. Its last sector is sector 209838,
the default choice. This is also the last sector on /dev/loop3.
Finally, the “w” command writes the new partition table through
/dev/loop3 to the disk image.
Resize Root File System
The following commands will expand the root file system to the size of the root partition.bash$ kpartx -a $loop_dev /dev/mapper/loop3p1: mknod for loop3p1 failed: File existsThe “kpartx -a” command creates device nodes for the partitions in the disk image. The output of “kpartx –a” (“mknod for loop3p1 failed”) seems to be a bug in my system. As far as I can tell, the creation and deletion of loop3p1 occur normally.
Another thing worth noting: kpartx and fdisk use different naming conventions. kpartx uses “/dev/mapper/device_name”, for example ”/dev/mapper/loop3p1″. fdisk uses “/dev/device_name”, such as “/dev/loop3p1″. This is because kpartx works with the device mapper.
Now run “fsck” to check the file system before resizing it. In fact, some file systems can’t be resized until they are checked.
bash$ fsck -f /dev/mapper/loop3p2 fsck from util-linux 2.19.1 e2fsck 1.41.14 (22-Dec-2010) Filesystem did not have a UUID; generating one. Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/mapper/loop3p2: ***** FILE SYSTEM WAS MODIFIED ***** /dev/mapper/loop3p2: 957/6000 files (0.2% non-contiguous), 8173/49152 blocksThe “-f” option forces a run even when the file system seems clean.
Finally, resize the root file system.
bash$ resize2fs /dev/mapper/loop3p2 resize2fs 1.41.14 (22-Dec-2010) Resizing the filesystem on /dev/mapper/loop3p2 to 100352 (1k) blocks. The filesystem on /dev/mapper/loop3p2 is now 100352 blocks long. bash$ kpartx -d $loop_devAfter resizing, “kpartx -d” reverses the changes made by “kpartx -a”.
Detach From Loop Device
The final step is to detach the image file from the loop device.bash$ losetup –d $loop_dev That’s it. The disk image is now ready to be used in a live USB or copied to a hard disk.
From: http://macbruins.wordpress.com
After creating my OpenWRT live USB (Easy Live USB for x86 OpenWRT), I wanted to use it on an older PC but ran into a problem: its BIOS does not support booting from USB. I had two choices. One was to boot up Linux from CD then switching to USB drive. The other was to get a CD bootloader that can read USB drives. Not wanting to do more work, I went searching and found Plop Boot Manager. It is very impress. Compact but full of features. It handles multiboot. It works with many bootloaders. It can boot OS on USB or CD without BIOS support. It even has a great GUI reminiscent of video arcade games. And it’s free. Do take a look.
But if you just want to get down to business, I have a ready-to-use CD image (plpbt_hiddenusb.iso on my SkyDrive). Just insert the CD and plug in your USB drive. Plop Boot Manager will do the rest.
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