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I have noticed the following option in the kernel: CONFIG_DEVTMPFS

Device Drivers -> Generic Driver Options -> Maintain devtmpfs to mount at /dev

And I see that it is enabled by default in the Debian distribution kernel 3.2.0-4-amd64

I am trying to understand what difference this option brings. Without this option, /dev is mounted as tmpfs , with this option, it is mounted as devtmpfs. Other than that, I don't see any difference.

The help did not clarify it for me either:

This creates a tmpfs/ramfs filesystem instance early at bootup. In this filesystem, the kernel driver core maintains device nodes with their default names and permissions for all registered devices with an assigned major/minor number.

It provides a fully functional /dev directory, where usually udev runs on top, managing permissions and adding meaningful symlinks.

In very limited environments, it may provide a sufficient functional /dev without any further help. It also allows simple rescue systems, and reliably handles dynamic major/minor numbers.

Could somebody please explain the difference between using CONFIG_DEVTMPFS vs the standard /dev?

1 Answer 1

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devtmpfs is a file system with automated device nodes populated by the kernel. This means you don't have to have udev running nor to create a static /dev layout with additional, unneeded and not present device nodes. Instead the kernel populates the appropriate information based on the known devices.

On the other hand the standard /dev handling requires either udev, an additional daemon running or to statically create device nodes on /dev.

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    Does it really mean, I don't need udev? The help says It provides a fully functional /dev directory, where usually udev runs on top, managing permissions and adding meaningful symlinks. If kernel populates /dev, what is there left to do for udev ?
    – user1968963
    Jun 2, 2013 at 9:23
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    In most circumstances you need udev. Directly from your quote, udev handles managing permissions and adding meaningful symlinks as well as running external scripts, notifying desktop environments etc.
    – Ulrich Dangel
    Jun 2, 2013 at 9:30
  • So does that mean it's better to use devtmpfs instead of tmpfs for /dev?
    – CMCDragonkai
    Jun 5, 2014 at 9:11
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    @CMCDragonkai yes, but your distribution should take care of that anyway
    – Ulrich Dangel
    Jun 18, 2014 at 12:41

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