Automount under mdev; looking for testers
 

More beta-testing, and some "shiney" for mdev users... yes, we now
have automount. I have no problem with manually mounting usb
drives/keys/cameras/etc, but some people insist on automount. I've
worked out how to implement automounting under mdev. I've got it
working on a machine at home, but we should have more testing before
posting this in the Gentoo mdev wiki.

There are a few preliminary setup steps required first. Everything
except part 4) b) is done as root. 4) b) is done by each regular user
that needs to unmount USB-plugable devices.

1) If you haven't already done so, install programs "pmount" and "sudo"
emerge pmount sudo


2) Create directory /media (It *MUST* be "/media").


3) Regular user accounts that need to access FAT-formatted USB keys need
to be added to group "plugdev".


4) a) In /etc/sudoers.d create a file (if it doesn't exist). To the file
add a line like...

USERID HOSTNAME = (root) NOPASSWD: /bin/umount /media/*

Replace "USERID" and "HOSTNAME" with the actual regular userid and the
actual hostname. If you have 2 or more users that need to automount USB
devices, add a separate line for each one.

4) b) Yanking out a USB key or external drive, after writing, without
unmounting it first, "is not a good thing". Since the USB device is
automounted by root, a regular user needs to use sudo to unmount it.
That's why we installed sudo. E.g...
sudo /bin/umount /media/sdb1

To make things easy for lazy typists, create a 2-line executable
script "~/bin/um" in the regular user's home bin directory like so...

#/bin/bash
sudo /bin/umount /media/${1}

It can be executed as "um sdb1" to unmount /media/sdb1


5) In case something goes drastically wrong, you should have a bootable
CD or USB stick handy, to recover with.


When running with mdev instead of udev under Gentoo, device setup is
controlled by /etc/mdev.conf. There is a brief intro to the syntax at
http://git.busybox.net/busybox/plain/docs/mdev.txt

We will make one change to /etc/mdev.conf and add a script to /lib/mdev/

1) Make a backup copy of /etc/mdev.conf

cp /etc/mdev.conf /etc/mdev.conf.000

If stuff goes terribly wrong, you can boot from recovery media and
revert to the previous version, i.e.

cp /etc/mdev.conf.000 /etc/mdev.conf


2) Change a line in /etc/mdev.conf from
sd[a-z].* root:disk 660 */lib/mdev/usbdisk_link

to

sd[a-z].* root:disk 660 */lib/mdev/usbdisk_automount


3) Take the file "usbdisk_automount" (listedbelow) and copy it to
/lib/mdev/usbdisk_automount and remember to set it executable, e.g.

chmod 744 /lib/mdev/usbdisk_automount

Automounting should work now; rebooting is not required. Plug in USB
keys/hard-drives/card-readers/direct-connection-to-cameras and play
around with them.

NOTES
=====

1) Sorry, pmount is hard-coded to mount in /media, e.g. /media/sdb1, and
similar. If you want it mounting elsewhere, please submit patches to
upstream.

2) If you connect a device (key or hard drive) formatted with a posix
filesystem (ext2/3/4, reiserfs, btrfs, etc) file permissions will apply
as usual. I.e. a regular user won't be able to modify/delete files
owned by other users (including root). The various FAT variants do not
support posix file permissions. pmount arbitrarily assigns user:root
and group:plugdev to all files+directories on FAT-based filesystems. By
using the "--umask 007" option in pmount, all files on FAT-based devices
can be read+written by root and members of the plugdev group.

3) For the beta testing, I've enabled debug logging to a temporary log
file /dev/shm/mdevlog.txt

4) Does anyone have a USB key or memory card that has the pathological
setup where the entire stick is a FAT partition, without a partition
table? If so, can you please let me know if automounting works with it?
If not please...

* unplug the device
* delete the file /dev/shm/mdevlog.txt
* plug the device in
* wait a few seconds and unplug it
* email me the contents of /dev/shm/mdevlog.txt

5) usbdisk_automount begins below

#!/bin/bash
#
# At bootup, "mdev -s" is called. It does not pass any environmental
# variables other than MDEV. If no ACTION variable is passed, exit
# the script.
if [ "X${ACTION}" == "X" ] ; then exit 0 ; fi
#
# Execute only if the device already exists; otherwise exit
if [ ! -b ${MDEV} ] ; then exit 0 ; fi
#
# Also only execute for partitions, not the underlying disks.
if [ "X${DEVTYPE}" != "Xpartition" ] ; then exit 0 ; fi

# Debug data dump.
exec 3>> /dev/shm/mdevlog.txt
echo "=============== * ${SEQNUM}" >&3
/usr/bin/printenv >&3
exec 3>&-

#
# The "add" action.
if [ "X${ACTION}" == "Xadd" ] ; then
#
# Create the directory in /media
mkdir -p /media/${MDEV}
#
# Mount the directory in /media
pmount --umask 007 --noatime /dev/${MDEV}
#
# The "remove" action.
elif [ "X${ACTION}" == "Xremove" ] ; then
#
# Unmount the directory in /media
umount /media/${MDEV}
#
# Delete the directory in /media
rm -rf /media/${MDEV}
fi


--
Walter Dnes <waltdnes@waltdnes.org>

Automount under mdev; looking for testers
 

On May 29, 2012 5:23 AM, "Walter Dnes" <waltdnes@waltdnes.org> wrote:

>

> *More beta-testing, and some "shiney" for mdev users... yes, we now

> have automount. *I have no problem with manually mounting usb

> drives/keys/cameras/etc, but some people insist on automount. *I've

> worked out how to implement automounting under mdev. *I've got it

> working on a machine at home, but we should have more testing before

> posting this in the Gentoo mdev wiki.

>

> *There are a few preliminary setup steps required first. *Everything

> except part 4) b) is done as root. *4) b) is done by each regular user

> that needs to unmount USB-plugable devices.

>

> 1) If you haven't already done so, install programs "pmount" and "sudo"

> emerge pmount sudo

>

>

> 2) Create directory /media (It *MUST* be "/media").

>

>

> 3) Regular user accounts that need to access FAT-formatted USB keys need

> to be added to group "plugdev".

>

>

> 4) a) In /etc/sudoers.d create a file (if it doesn't exist). *To the file

> add a line like...

>

> USERID *HOSTNAME = (root) NOPASSWD: /bin/umount /media/*

>

> Replace "USERID" and "HOSTNAME" with the actual regular userid and the

> actual hostname. *If you have 2 or more users that need to automount USB

> devices, add a separate line for each one.

>

> 4) b) Yanking out a USB key or external drive, after writing, without

> unmounting it first, "is not a good thing". *Since the USB device is

> automounted by root, a regular user needs to use sudo to unmount it.

> That's why we installed sudo. *E.g...

> sudo /bin/umount /media/sdb1

>

> To make things easy for lazy typists, create a 2-line executable

> script "~/bin/um" in the regular user's home bin directory like so...

>

> #/bin/bash

> sudo /bin/umount /media/${1}

>

> It can be executed as "um sdb1" to unmount /media/sdb1

>

>

> 5) In case something goes drastically wrong, you should have a bootable

> CD or USB stick handy, to recover with.

>

>

> *When running with mdev instead of udev under Gentoo, device setup is

> controlled by /etc/mdev.conf. *There is a brief intro to the syntax at

> http://git.busybox.net/busybox/plain/docs/mdev.txt

>

> *We will make one change to /etc/mdev.conf and add a script to /lib/mdev/

>

> 1) Make a backup copy of /etc/mdev.conf

>

> cp /etc/mdev.conf /etc/mdev.conf.000

>

> *If stuff goes terribly wrong, you can boot from recovery media and

> revert to the previous version, i.e.

>

> cp /etc/mdev.conf.000 /etc/mdev.conf

>

>

> 2) Change a line in /etc/mdev.conf from

> sd[a-z].* * * * root:disk 660 */lib/mdev/usbdisk_link

>

> to

>

> sd[a-z].* * * * root:disk 660 */lib/mdev/usbdisk_automount

>

>

> 3) Take the file "usbdisk_automount" (listedbelow) and copy it to

> /lib/mdev/usbdisk_automount and remember to set it executable, e.g.

>

> chmod 744 /lib/mdev/usbdisk_automount

>

> Automounting should work now; rebooting is not required. *Plug in USB

> keys/hard-drives/card-readers/direct-connection-to-cameras and play

> around with them.

>

> NOTES

> =====

>

> 1) Sorry, pmount is hard-coded to mount in /media, e.g. /media/sdb1, and

> similar. *If you want it mounting elsewhere, please submit patches to

> upstream.

>

> 2) If you connect a device (key or hard drive) formatted with a posix

> filesystem (ext2/3/4, reiserfs, btrfs, etc) file permissions will apply

> as usual. *I.e. a regular user won't be able to modify/delete files

> owned by other users (including root). *The various FAT variants do not

> support posix file permissions. *pmount arbitrarily assigns user:root

> and group:plugdev to all files+directories on FAT-based filesystems. *By

> using the "--umask 007" option in pmount, all files on FAT-based devices

> can be read+written by root and members of the plugdev group.

>

> 3) For the beta testing, I've enabled debug logging to a temporary log

> file /dev/shm/mdevlog.txt

>

> 4) Does anyone have a USB key or memory card that has the pathological

> setup where the entire stick is a FAT partition, without a partition

> table? *If so, can you please let me know if automounting works with it?

> If not please...

>

> * unplug the device

> * delete the file /dev/shm/mdevlog.txt

> * plug the device in

> * wait a few seconds and unplug it

> * email me the contents of /dev/shm/mdevlog.txt

>

> 5) usbdisk_automount begins below

>

> #!/bin/bash

> #

> # At bootup, "mdev -s" is called. *It does not pass any environmental

> # variables other than MDEV. *If no ACTION variable is passed, exit

> # the script.

> if [ "X${ACTION}" == "X" ] ; then exit 0 ; fi

> #

> # Execute only if the device already exists; otherwise exit

> if [ ! -b ${MDEV} ] ; then exit 0 ; fi

> #

> # Also only execute for partitions, not the underlying disks.

> if [ "X${DEVTYPE}" != "Xpartition" ] ; then exit 0 ; fi

>

> # Debug data dump.

> exec 3>> /dev/shm/mdevlog.txt

> echo "=============== * ${SEQNUM}" >&3

> /usr/bin/printenv >&3

> exec 3>&-

>

> #

> # The "add" action.

> if [ "X${ACTION}" == "Xadd" ] ; then

> #

> # Create the directory in /media

> * mkdir -p /media/${MDEV}

> #

> # Mount the directory in /media

> * pmount --umask 007 --noatime /dev/${MDEV}

> #

> # The "remove" action.

> elif [ "X${ACTION}" == "Xremove" ] ; then

> #

> # Unmount the directory in /media

> * umount /media/${MDEV}

> #

> # Delete the directory in /media

> * rm -rf /media/${MDEV}

> fi

>

>


A quick question : for automounting to work, do you need to do sysctl -w kernel.hotplug=/sbin/mdev , or is it optional?


Rgds,

Automount under mdev; looking for testers
 

On Tue, May 29, 2012 at 09:13:24AM +0700, Pandu Poluan wrote

> A quick question : for automounting to work, do you need to do sysctl -w
> kernel.hotplug=/sbin/mdev , or is it optional?

Thanks, I'll have to document that. In .config, I think you need
"CONFIG_HOTPLUG=y". I don't know if the kernel can even be built
without it. What output do you get from the command

cat /proc/sys/kernel/hotplug

I get...

/sbin/mdev

That's what you need. *IF THAT IS NOT THE CASE FOR YOU* the docs at
http://git.busybox.net/busybox/plain/docs/mdev.txt give 2 options...

1) If you have a proc file system (yes we do), the way to do it is

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


2) For embedded systems without a proc filesystem, you can

sysctl -w kernel.hotplug=/sbin/mdev


Option 2 would probably also work for Gentoo, but the proc filesystem
makes things a lot easier.


In my case hotplug support was enabled and /sbin/mdev was already
listed in /proc/sys/kernel/hotplug. Google turns up a lot of
documentation for mdev on stripped down embedded systems. Trying to
apply it to a desktop PC is breaking new ground.

--
Walter Dnes <waltdnes@waltdnes.org>