> On Mar 8, 2016, at 7:29 AM, Patrick <[email protected]> wrote:
>
> On Fri, Mar 4, 2016 at 9:09 PM, 张云 <[email protected] <mailto:[email protected]>>
> wrote:
> First your must know exactly how linux boot (not at source code level).
>
> Most recent linux distributions boot as
>
> grub —> kernel —> initramfs’ /init executable
>
> All the userspace affair is started by initramfs’ /init. Kernel no longer
> join the boot process.
>
> >From you description, I think you were blocked by the initramfs concept.
> >Initramfs is the first root filesystem and reside in memeory.
> It’s loaded by grub, and the kernel automatically mount it, execute the
> /init. The /init executable can do some extra initialisation
> and switch to the real root filesystem on disk.
> for detail /Documentaion/filesystems/ramfs-rootfs-initramfs
>
> Hope that would be useful to your.
>
> Thanks for the response. I was able to get a minimal boot using the files in
> the mini.iso image from Ubuntu. I just copied the kernel and the ramdisk
> image from that iso, and these have given me enough to start learning some
> things. It is still just dropping me into the prompt for the ramdisk image,
> so the kernel hasn't yet made the switch over to root filesystem on a drive,
> but this is at least enough to get me started.
>
> One thing I noticed that confused me was the result of the commands pasted
> below. It looks like the partition table on the disk image might be getting
> messed up. But, interestingly enough, it still seems to allow me to use the
> image for booting. In spite of this, fdisk is giving me strange output when I
> ask it to print out the partition tables after I build a file system on the
> disk image using mkfs. When I look at the disk image using gparted, on the
> other hand, it actually looks OK.
>
> It looks like I might be using mkfs incorrectly. Can anyone see anything
> obvious that I am doing wrong?
>
> ==============
>
> dd if=/dev/zero of=./disk.img bs=1M count=1000
> sudo losetup /dev/loop0 ./disk.img
> sudo fdisk /dev/loop0
> (commands in fdisk)
> > n (new partition)
> > p (primary partition)
> > 1 (partition number)
> > (default start and end for partition)
> > t (change type of partition)
> > b (change type of partition to FAT32)
> > a (set boot flag)
> > 1 (set boot flag for first partition)
> > w (write changes)
> fdisk -lu /dev/loop0
> Disk /dev/loop0
> : 1048 MB, 1048576000 bytes
> 123 heads, 59 sectors/track, 282 cylinders, total 2048000 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: 0x7b9351bf
>
> Device Boot Start End Blocks Id System
> /dev/loop0p1 * 2048 2047999 1022976 b W95 FAT32
>
The problem is caused by the command below
> mkfs -t vfat /dev/loop0
/dev/loop0 is the whole disk, and /dev/loop0p1 is the partition.
The command make a file system on the disk, thus overrides the disk’s partition
table.
I guess that it is the partition on which you want to make a filesystem.
The right command is
mkfs -t ext2 /dev/loop0p1
We prefer ext2,3,4 to fat32 on linux.
> fdisk -lu /dev/loop0
> Disk /dev/loop0: 1048 MB, 1048576000 bytes
> 255 heads, 63 sectors/track, 127 cylinders, total 2048000 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
>
> ==============
>
> Thanks,
> Patrick
>
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