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On Sat, Sep 17, 2011 at 6:27 PM, Dale <rdalek1967@×××××.com> wrote: |
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> Mark Knecht wrote: |
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> I think there are only a few that has that flag, at least that I would put |
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> in the init thingy anyway. Maybe this is something that the devs will work |
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> on if it can be done. May be a big if there. |
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> |
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> That is the guide I am trying to go by but I think I am missing something. |
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> This is the script they have posted: |
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> |
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> #!/bin/busybox sh |
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> |
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> # Mount the /proc and /sys filesystems. |
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> mount -t proc none /proc |
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> mount -t sysfs none /sys |
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> |
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> # Do your stuff here. |
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> echo "This script mounts rootfs and boots it up, nothing more!" |
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> |
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> # Mount the root filesystem. |
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> mount -o ro /dev/sda1 /mnt/root |
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> |
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> # Clean up. |
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> umount /proc |
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> umount /sys |
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> |
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> # Boot the real thing. |
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> exec switch_root /mnt/root /sbin/init |
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> |
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> That doesn't really make much sense to me. First it mounts the stuff then |
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> umounts it right after that. Huh? Is the relevant part the "mount -o ro |
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> /dev/sda1 /mnt/root" ? Then the exec switch_root part after that? The rest |
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> seems to cancel each other out. |
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> |
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> Looking forward to that light bulb moment here. ;-) |
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|
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Here's how I read it. |
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First, it mounts /proc and /sys, since just about anything is going to |
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need at least one of those. |
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|
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Second, it mounts your (desired) / filesystem at /mnt/root. |
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|
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Third, it unmounts /proc and /sys. |
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|
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Fourth, it switches out / with the filesystem it already mounted at |
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/mnt/root. This is similar (idential) to chroot. At the _same_ time, |
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it launches your init script. |
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Your init script launches and sees a / without a /proc or a /sys. The |
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/ it sees is what _was_ /mnt/root only moments before. The stuff that |
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was originally at / is no longer accessible. (Which, incidentally, is |
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why you unmount /proc and /sys; nothing would be able to get to those |
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particular mounted filesystems, since everything else gets to see the |
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world with /mnt/root/ as the /. |
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|
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Your init script (the one at /sbin/init), seeing itself in a fresh, |
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needs-to-be-booted system, mounts /proc, /sys, etc...everything the |
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init script is configured to do. |
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|
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-- |
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:wq |
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