[gentoo-user] Automount under mdev; looking for testers

["Walter Dnes" <waltdnes@waltdnes.org>]

  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>