- the former had stayed around for many months with maintainer
claiming that everything works fine
- the latter had stayed, period.
- - the devfs maintainer/author disappeared and stoped maintaining
+ - the devfs maintainer/author disappeared and stopped maintaining
the code.
Q: But udev will not automatically load a driver if a /dev node is opened
hardware in memory, then use something else to manage your modules
(scripts, modules.conf, etc.) This is not a task for udev.
+Q: But I love that feature of devfs, please?
+A: The devfs approach caused a lot of spurious modprobe attempts as
+ programs probed to see if devices were present or not. Every probe
+ attempt created a process to run modprobe, almost all of which were
+ spurious.
+
Q: I really like the devfs naming scheme, will udev do that?
A: Yes, udev can create /dev nodes using the devfs naming policy. A
configuration file needs to be created to map the kernel default names
- to the devfs names. See the initial udev.conf.devfs file in the udev
+ to the devfs names. See the initial udev.rules.devfs file in the udev
release. It is the start of such a configuration file. If there are
any things missing, please let the udev authors know.
Q: Will udev support symlinks?
A: Yes, It now does. Multiple symlinks per device node too.
-Q: How will udev support changes to device permissions?
-A: On shutdown, udev will save the state of existing device permissions to
- its database, and then used the on the next boot time.
-
Q: How will udev handle the /dev filesystem?
A: /dev can be a ramfs, or a backing filesystem. udev does not care what
kind of filesystem it runs on.
A: udev will be placed in initramfs and run for every device that is found.
Work to get this implemented is still underway.
+Q: Can I use udev to automount a USB device when I connect it?
+A: Technically, yes, but udev is not intended for this. Projects that do
+ automount hotplugged storage devices are:
+ * Usb-mount http://users.actrix.co.nz/michael/usbmount.html
+ * devlabel http://linux.dell.com/projects.shtml#devlabel
+
+ Alternatively, it is easy to add the following to fstab:
+ /udev/pendrive /pendrive vfat user,noauto 0 0
+
+ This means that users can access the device with:
+ $ mount /pendrive
+ And don't have to be root but will get full permissions on /pendrive.
+ This works even without udev if /udev/pendrive is replaced by /dev/sda1
+
+Q: Are there any security issues that I should be aware of?
+A: When using dynamic device numbers, a given pair of major/minor numbers may
+ point to different hardware over time. If a user has permission to access a
+ specific device node directly and is able to create hard links to this node,
+ he or she can do so to create a copy of the device node. When the device is
+ unplugged and udev removes the device node, the user's copy remains.
+ If the device node is later recreated with different permissions the hard
+ link can still be used to access the device using the old permissions.
+ (The same problem exists when using PAM to change permissions on login.)
+
+ The simplest solution is to prevent the creation of hard links by putting
+ /dev in a separate filesystem (tmpfs, ramfs, ...).
+
Q: I have other questions about udev, where do I ask them?
A: The linux-hotplug-devel mailing list is the proper place for it. The
address for it is linux-hotplug-devel@lists.sourceforge.net