FAQs (XUELK)

Info Box Applies to SBC Lynx

Introduction

This page collects Frequently Asked Questions (FAQs) regarding AXEL ULite and SBC Lynx Embedded Linux Kit (XUELK).

Q: How to enable USB storage auto-mount/unmount?

A: USB storage auto-mount can be enabled by adding specific udev rules. The following example has been tested with this file system: https://mirror.dave.eu/lynx/xuelk-1.1.0/xuelk-1.1.0_lynx-image-networking-sbc-lynx.tar.bz2, and makes use of two files.

The first one is called automount.rules. It contains the additional rules, and it has to be copied in /etc/udev/rules.d/. It looks like this:

root@sbc-lynx:~# cat /etc/udev/rules.d/automount.rules
# There are a number of modifiers that are allowed to be used in some
# of the different fields. They provide the following subsitutions:
#
# %n the "kernel number" of the device.
#    For example, 'sda3' has a "kernel number" of '3'
# %e the smallest number for that name which does not matches an existing node
# %k the kernel name for the device
# %M the kernel major number for the device
# %m the kernel minor number for the device
# %b the bus id for the device
# %c the string returned by the PROGRAM
# %s{filename} the content of a sysfs attribute
# %% the '%' char itself
#

# Media automounting
SUBSYSTEM=="block", ACTION=="add"    RUN+="/etc/udev/scripts/mount.sh"
SUBSYSTEM=="block", ACTION=="remove" RUN+="/etc/udev/scripts/mount.sh"

The second file is a script that can be copied in /etc/udev/scripts/. It looks like this:

root@sbc-lynx:~# cat /etc/udev/scripts/mount.sh
#!/bin/sh
#
# Called from udev
#
# Attempt to mount any added block devices and umount any removed devices


MOUNT="/bin/mount"
PMOUNT="/usr/bin/pmount"
UMOUNT="/bin/umount"
for line in `grep -v ^# /etc/udev/mount.blacklist`
do
        if [ ` expr match "$DEVNAME" "$line" ` -gt 0 ];
        then
                logger "udev/mount.sh" "[$DEVNAME] is blacklisted, ignoring"
                exit 0
        fi
done

automount() {
        name="`basename "$DEVNAME"`"

        ! test -d "/media/$name" && mkdir -p "/media/$name"
        # Silent util-linux's version of mounting auto
        if [ "x`readlink $MOUNT`" = "x/bin/mount.util-linux" ] ;
        then
                MOUNT="$MOUNT -o silent"
        fi

        if ! $MOUNT -t auto $DEVNAME "/media/$name"
        then
                #logger "mount.sh/automount" "$MOUNT -t auto $DEVNAME \"/run/media/$name\" failed!"
                rm_dir "/media/$name"
        else
                logger "mount.sh/automount" "Auto-mount of [/media/$name] successful"
                touch "/tmp/.automount-$name"
        fi
}

rm_dir() {
        # We do not want to rm -r populated directories
        if test "`find "$1" | wc -l | tr -d " "`" -lt 2 -a -d "$1"
        then
                ! test -z "$1" && rm -r "$1"
        else
                logger "mount.sh/automount" "Not removing non-empty directory [$1]"
        fi
}

if [ "$ACTION" = "add" ] && [ -n "$DEVNAME" ] && [ -n "$ID_FS_TYPE" ]; then
        if [ -x "$PMOUNT" ]; then
                $PMOUNT $DEVNAME 2> /dev/null
        elif [ -x $MOUNT ]; then
                $MOUNT $DEVNAME 2> /dev/null
        fi

        # If the device isn't mounted at this point, it isn't
        # configured in fstab (note the root filesystem can show up as
        # /dev/root in /proc/mounts, so check the device number too)
        if expr $MAJOR "*" 256 + $MINOR != `stat -c %d /`; then
                grep -q "^$DEVNAME " /proc/mounts || automount
        fi
fi



if [ "$ACTION" = "remove" ] && [ -x "$UMOUNT" ] && [ -n "$DEVNAME" ]; then
        for mnt in `cat /proc/mounts | grep "$DEVNAME" | cut -f 2 -d " " `
        do
                $UMOUNT $mnt
        done

        # Remove empty directories from auto-mounter
        name="`basename "$DEVNAME"`"
        test -e "/tmp/.automount-$name" && rm_dir "/media/$name"
fi

After creating these two files, restart udev to make the changes take effect:

udevadm control --reload-rules

The following console dump shows the process of auto-mounting/auto-unmounting of a FAT32 partition, stored on a USB flash drive.

root@sbc-lynx:~# [  611.238221] usb 1-1: new high-speed USB device number 3 using ci_hdrc
[  611.406307] usb-storage 1-1:1.0: USB Mass Storage device detected
[  611.424566] scsi1 : usb-storage 1-1:1.0
[  612.431396] scsi 1:0:0:0: Direct-Access     Generic  FIash Disk       8.07 PQ: 0 ANSI: 2
[  612.456387] sd 1:0:0:0: [sda] 15663104 512-byte logical blocks: (8.01 GB/7.46 GiB)
[  612.474787] sd 1:0:0:0: [sda] Write Protect is off
[  612.485226] sd 1:0:0:0: [sda] No Caching mode page found
[  612.491238] sd 1:0:0:0: [sda] Assuming drive cache: write through
[  612.504934] sd 1:0:0:0: [sda] No Caching mode page found
[  612.511000] sd 1:0:0:0: [sda] Assuming drive cache: write through
[  612.577162]  sda: sda1
[  612.591581] sd 1:0:0:0: [sda] No Caching mode page found
[  612.596934] sd 1:0:0:0: [sda] Assuming drive cache: write through
[  612.606655] sd 1:0:0:0: [sda] Attached SCSI removable disk
[  613.219100] FAT-fs (sda1): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.

root@sbc-lynx:~# mount
rootfs on / type rootfs (rw)
192.168.0.13:/opt/nfsroot/lynx/xuelk-1.1.0-networking on / type nfs (rw,relatime,vers=3,rsize=4096,wsize=4096,namlen=255,hard,nolock,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=192.168.0.13,mountvers=3,mountproto=tcp,local_lock=all,addr=192.168.0.13)
devtmpfs on /dev type devtmpfs (rw,relatime,size=220568k,nr_inodes=55142,mode=755)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /var/volatile type tmpfs (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620)
/dev/sda1 on /media/sda1 type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
...
root@sbc-lynx:~# [  631.627230] usb 1-1: USB disconnect, device number 3
root@sbc-lynx:~# mount
rootfs on / type rootfs (rw)
192.168.0.13:/opt/nfsroot/lynx/xuelk-1.1.0-networking on / type nfs (rw,relatime,vers=3,rsize=4096,wsize=4096,namlen=255,hard,nolock,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=192.168.0.13,mountvers=3,mountproto=tcp,local_lock=all,addr=192.168.0.13)
devtmpfs on /dev type devtmpfs (rw,relatime,size=220568k,nr_inodes=55142,mode=755)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /var/volatile type tmpfs (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620)
root@sbc-lynx:~# ls -la /media/
drwxr-xr-x    7 root     root          4096 Mar  1  2017 .
drwxr-xr-x   17 root     root          4096 Feb 28  2017 ..
drwxr-xr-x    2 root     root          4096 Dec 13 15:55 mmcblk0p1
drwxr-xr-x    2 root     root          4096 Feb  2 16:02 mmcblk0p2