[1.16.2/mdev] "Can't open /proc/sys/kernel/hotplug"

Harald Becker ralda at gmx.de
Mon May 30 10:12:27 UTC 2011

 Hi Gilles!

> I used a sample rc.d script that I found in the archives of this list,
> but the appliance has no /proc/sys/kernel/hotplug:
> Does it matter? Could someone tell me how to set things up correctly?

Looks like your kernel has not enabled hotplug-ing. That way you are
able to use static device file creation in a more or less reliable way.
You are not forced to use mdev or any other way of dynamic device file
creation, if you carefully look at your kernel device lists and create
corresponding device files (different kernels/systems may use different
major/minor numbers). However you can use mdev (it is not wrong), but
you need to reseed your device file system manually whenever you change
the connected devices.

On system startup do "mdev -s" for an initial device file system seed
and skip the hotplug initialization. After removing devices, just delete
the corresponding device files manually. After connecting new devices,
redo "mdev -s" to update your device file system. That works on several
of my x86 systems, including USB devices.

>   start) echo "Starting mdev...";
>          echo /sbin/mdev > /proc/sys/kernel/hotplug;
>          /sbin/mdev -s;
>          ;;

1. Just comment out that hotplug setting line:

# echo /sbin/mdev > /proc/sys/kernel/hotplug

2. Restart your system

3. Do "mdev -s" as root, after adding new devices to your system (may be
you can add this to scripts preparing new devices for usage, e.g. before

... than you shall be fine, at least on newer kernels with enabled sysfs.


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