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dm-verity: don't make read-only-rootfs sound like a requirement

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Adding to your local.conf right out of the gate:

  EXTRA_IMAGE_FEATURES = "read-only-rootfs"

while you are trying to sort out other things can be just another
complication to an already steep learning curve.

For example, I found simply enabling this with systemd caused:

  systemd[1]: Failed to fork off sandboxing environment for executing generators: Protocol error
  [!!!!!!] Failed to start up manager.
  systemd[1]: Freezing execution.

While I'd like to get to the root cause of that, it doesn't change that
things boot fine w/o adding to EXTRA_IMAGE_FEATURES, even though the
rootfs is still read-only courtesy of dm-verity.

Reword things so as to make it clear it isn't strictly a hard requirement
and hence can be delayed as people work through their implementation.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
This commit is contained in:
Paul Gortmaker
2023-05-10 11:04:40 -04:00
committed by Armin Kuster
parent 2c8c86f97e
commit 1cb3f6988a
1 changed files with 9 additions and 2 deletions
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11
docs/dm-verity.txt
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@@ -53,11 +53,18 @@ conf/local.conf and conf/bblayers.conf from the oe-init-build-env
Firstly, you need the meta-security layer to conf/bblayers.conf along with
the dependencies it has -- see the top level meta-security README for that.
Next, assuming you'll be using dm-verity for validation of your rootfs,
you'll need to enable read-only rootfs support in your local.conf with:
Note that if you are using dm-verity for your rootfs, then it enforces a
read-only mount right at the kernel level, so be prepared for issues such
as failed creation of temporary files and similar.
Yocto does support additional checks and changes via setting:
EXTRA_IMAGE_FEATURES = "read-only-rootfs"
...but since read-only is enforced at the kernel level already, using
this feature isn't a hard requirement. It may be best to delay/defer
making use of this until after you've established basic booting.
For more details, see the associated documentation:
https://docs.yoctoproject.org/dev/dev-manual/read-only-rootfs.html