Automatically mount removable media
From ArmadeusWiki
When using USB key or MMC/SD in a final application, it could be useful if these media were automatically mount when inserted by the user. We will explain you how to implement this behaviour in this tutorial.
Default case (mdev)
- If you are using default armadeus rootfs, hotplugging is handled by an application called mdev. This can be easily checked with:
# cat /proc/sys/kernel/hotplug /sbin/mdev
- It means that each time Linux kernel detect a new device it will call /sbin/mdev program with specific parameters.
- You can configure mdev with its config file: /etc/mdev.conf. To add automatic mount of USB and SD/MMC devices you can apply the following changes (- -> remove line, + -> add line) in the configuration file:
# Block devices
-sd[a-z].* 0:6 660
-mmcblk[0-9].* 0:6 660
+sd[a-z] 0:6 660
+mmcblk[0-9] 0:6 660
+sd[a-z][0-9] 0:6 660 */lib/mdev/automounter.sh
+mmcblk[0-9]p[0-9] 0:6 660 */lib/mdev/automounter.sh
- this way mdev will call a script named /lib/mdev/automount.sh each time a USB drive or an MMC/SD (with a recognized partition table) is plugged in.
- create directory /lib/mdev
# mkdir /lib/mdev
- then we will have to write what this script is going to do. So take your favorite editor and fill /lib/mdev/automounter.sh with:
# vi /lib/mdev/automounter.sh
#!/bin/sh
destdir=/media
my_umount()
{
if grep -qs "^/dev/$1 " /proc/mounts ; then
umount "${destdir}/$1";
fi
[ -d "${destdir}/$1" ] && rmdir "${destdir}/$1"
}
my_mount()
{
mkdir -p "${destdir}/$1" || exit 1
if ! mount -t auto -o sync "/dev/$1" "${destdir}/$1"; then
# failed to mount, clean up mountpoint
rmdir "${destdir}/$1"
exit 1
fi
}
case "${ACTION}" in
add|"")
my_umount ${MDEV}
my_mount ${MDEV}
;;
remove)
my_umount ${MDEV}
;;
esac
# chmod a+x /lib/mdev/automounter.sh
- As we now use /media to create dynamic mount points we will move it from FLASH to RAM by using a tmpfs mount. Take your favorite editor again and edit /etc/fstab file to add it the following line:
...
usbfs /proc/bus/usb usbfs defaults 0 0
+tmpfs /media tmpfs defaults 0 0
- Then, reboot and everything should now work :-). For example when plugging a MMC/SD you will get:
# mmc0: host does not support reading read-only switch. assuming write-enable. mmc0: new SD card at address 0002 mmcblk0: mmc0:0002 SD 1.87 GiB mmcblk0: p1 # ls -al /media/ total 32 drwxrwxrwt 3 root root 60 Jan 1 00:27 . drwxrwxr-x 18 root root 1248 Feb 6 2012 .. drwxrwxrwx 7 root root 16384 Jan 1 00:00 mmcblk0p1 # mount ... /dev/mmcblk0p1 on /media/mmcblk0p1 type vfat (rw,sync,fmask=0000,dmask=0000,allow_utime=0022,codepage=cp437,iocharset=iso8859-1)
- Don't forget that if you want to remove your device, you will have to manually umount it before. Example for a MMC/SD:
# umount /media/mmcblk0p1
Other cases
- well... in that cases I suppose you know what you're doing !:-)
- if using udev instead of mdev for example, then you will have to activate corresponding Buildroot packages (eg usbmount)
