Difference between revisions of "USB storage devices"

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(Add missing double quote to script)
(Auto-mounting with udev and systemd: Added compatability for larger USB hard drives, and MMC devices.)
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{{bc|<nowiki>
 
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# ignore sda*
 
# ignore sda*
KERNEL!="sd[b-z]*", GOTO="end"
+
KERNEL!="sd[b-z]*", GOTO="USB"
 +
# Also allow SD cards
 +
KERNEL!="mmcblk[0-9]p[0-9]", GOTO="MMC"
  
# run the script
+
# USB: run the script
ACTION=="add", ENV{ID_BUS}=="usb", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service"
+
LABEL="USB"
 +
ACTION=="add", ENV{ID_BUS}=="usb", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"
 +
ACTION=="add", ENV{ID_BUS}=="ata", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"
 +
 
 +
LABEL="MMC"
 +
ACTION=="add", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"
  
 
# exit
 
# exit

Revision as of 09:06, 16 July 2013

This document describes how to use the popular USB memory sticks with Linux. However, it is also valid for other devices such as digital cameras that act as if they were just a USB storage device.

Mounting USB devices

If you have an up-to-date system with the standard Arch kernel and a modern Desktop environment your device should just show up on your desktop, with no need to open a console.

Otherwise see sections below.

Auto-mounting with udev

See Udev:Auto mounting USB devices.

A lightweight solution to automount drives using udev, for single-user systems, is the following: create a file named /etc/udev/rules.d/automount.rules with the following content:

# ignore sda*
KERNEL!="sd[b-z]*", GOTO="end"

# run the script
ACTION=="add", ENV{ID_BUS}=="usb", ENV{DEVTYPE}=="partition", RUN+="domount %N"

# exit
LABEL="end"

and a file (executable by root) named /usr/lib/udev/domount with (set the variables on top to the correct values):

#!/bin/sh

#edit the following variables to suit your needs
MYUID=1000              # your user uid
MYGID=100               # your user gid
MYLOGIN=al              # your login
TERM=lxterminal         # your terminal emulator
MYSHELL=zsh             # your shell
export DISPLAY=:0       # your X display


TMPFILE=/run/automount.$RANDOM
DIR=$(grep -v '#' /etc/fstab | grep $* | awk '{print $2;}')
if [ -z "$DIR" ]; then
    LABEL=$(lsblk -no LABEL $*)
    if [ -z "$LABEL" ]; then
        UUID=$(lsblk -no UUID $*)
        if [ -z "$UUID" ]; then
            DIR=/run/media/"unknown"
        else
            DIR=/run/media/"$UUID"
        fi
    else
        DIR=/run/media/"$LABEL"
    fi
fi
mkdir -p $DIR

cat > $TMPFILE << EOF
#!/bin/sh
echo "$* was mounted on $DIR. "
cd $DIR
$MYSHELL
EOF
chmod a+x $TMPFILE

/bin/mount -o uid=$MYUID,gid=$MYGID $* $DIR
su $MYLOGIN -c "$TERM -t 'Terminal - $* mounted on $DIR' -e $TMPFILE"
/bin/umount $DIR

sleep 1; rm -f $TMPFILE

When a drive is inserted, it will be mounted, and a Terminal will pop-up. To umount the device, simply press Control+D in the terminal window. The mountpoint is looked for in /etc/fstab or, if absent, generated from the label of the partition.

If the terminal doesn't appear as expected, that may because wrong options are used. For example, in XFCE4, we use "Terminal -T title -e script-file instead"

Auto-mounting with udev and systemd

The above solution does not work, since the RUN directive is for only short processes, and udev enforces this; Scripts will be killed shortly after starting. Instead, the following solution based on the previous one uses systemd, udev and screen to create a more elegant solution.

First, we create a systemd service template (/etc/systemd/system/automount@.service):

[Unit]
Description=Automount removable storage

[Service]
Type=forking
ExecStart=/usr/lib/udev/domount %I

We also create a udev rule in /etc/udev/rules.d/automount.rules very similar to the previous solution.

# ignore sda*
KERNEL!="sd[b-z]*", GOTO="USB"
# Also allow SD cards
KERNEL!="mmcblk[0-9]p[0-9]", GOTO="MMC"

# USB: run the script
LABEL="USB"
ACTION=="add", ENV{ID_BUS}=="usb", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"
ACTION=="add", ENV{ID_BUS}=="ata", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"

LABEL="MMC"
ACTION=="add", ENV{DEVTYPE}=="partition", RUN+="/usr/bin/systemctl start automount@%N.service", GOTO="end"

# exit
LABEL="end"

The juice of the solution is placed in /usr/lib/udev/domount:

#!/bin/sh

#edit the following variables to suit your needs
MYUID=1000              # your user uid
MYGID=100               # your user gid
MYLOGIN="ME"            # your login


USERSCRIPT="/usr/lib/udev/domount_user";

BASE='/media'
DIR=`basename $*`;
i=0;
while [ -d "$BASE/$DIR" ]; do
  DIR="`basename $*`.$i";
  i=$((i+1));
done

mkdir -p "$BASE/$DIR" && /bin/mount -o uid=$MYUID,gid=$MYGID "$*" "$BASE/$DIR"

if [ -z "`su $MYLOGIN -c 'screen -ls | grep AUTOMOUNT'`" ]; then
  su $MYLOGIN -c "screen -dm -S AUTOMOUNT -t $DIR $USERSCRIPT $* $BASE $DIR";
  exit;
fi
su $MYLOGIN -c "screen -S AUTOMOUNT -X screen -t $DIR $USERSCRIPT $* $BASE $DIR";

and in /usr/lib/udev/domount_user:

#!/bin/sh
DEV="$1";
BASE="$2";
DIR="$3";

echo "$DEV mounted on $BASE/$DIR"
echo "Contents:"
ls --color=auto "$BASE/$DIR"
echo -e "\n------------------------------------\nExit shell to unmount when finished.";
while true; do
  d=$HOME;
  cd $BASE/$DIR
  bash
  cd $dir;

  echo "------------------------------------"
  lsof | grep $BASE/$DIR;
  if [ $? -eq 1 ]; then
    break;
  else
    echo "------------------------------------";
    echo "The above processes will block the unmount. Please end them.";
  fi
done

sudo /bin/umount "$BASE/$DIR" && sudo rmdir "$BASE/$DIR";

To access the screen session which controls the mounted partitions, simply run

$ screen -d -r AUTOMOUNT

I would suggest putting this in a command key shortcut, for example with xbindkeys to run in a terminal.

Manual mounting

Note: Before you decide that Arch Linux does not mount your USB device, be sure to check all available ports. Some ports might not share the same controller, preventing you from mounting the device.

Getting a kernel that supports usb_storage

If you do not use a custom-made kernel, you are ready to go, for all Arch Linux stock kernels are properly configured. If you do use a custom-made kernel, ensure it is compiled with SCSI-Support, SCSI-Disk-Support and usb_storage. If you use the latest udev, you may just plug your device in and the system will automatically load all necessary kernel modules. Older releases of udev would need hotplug installed too. Otherwise, you can do the same thing manually:

# modprobe usb-storage
# modprobe sd_mod      (only for non SCSI kernels)

Identifying device

First thing one need to access storage device is it's identifier assigned by kernel.

Using device node names ( /sd* )

This is the simplest way, but assigned name depends on order of insertion. Ways to get node name:

  • search in the output of dmesg for the kernel device name, you can use grep to help you find what you are looking for:
$ dmesg | grep -E "sd[a-z]"
  • List all available partition tables:
# fdisk -l
Note: If you cannot find your device you can use lsusb to verify that it is indeed recognized by the system.
Using UUID

Every drive creates a UUID (Universally Unique Identifier), these identifiers can be used to track individual drive no matter their device node (i.e. /dev/sda).

To find the current UUIDs execute (as root):

# blkid -o list -c /dev/null
device         fs_type  label     mount point        UUID
------------------------------------------------------------------------------------------
/dev/sda1      ext2               /boot              7f4cef7e-7ee2-489a-b759-d52ba23b692c
/dev/sda2      swap               (not mounted)      a807fff3-e89f-46d0-ab17-9b7ad3efa7b5
/dev/sda3      ext4               /                  81917291-fd1a-4ffe-b95f-61c05cfba76f
/dev/sda4      ext4               /home              c4c23598-19fb-4562-892b-6fb18a09c7d3
/dev/sdb1      ext4     X2        /mnt/X1            4bf265f7-da17-4575-8758-acd40885617b
/dev/sdc1      ext4     X1        /mnt/X2            4bf265f7-da17-4575-8758-acd40885617b
/dev/sdd1      ext4     Y2        /mnt/Y2            8a976a06-3e56-476f-b73a-ea3cad41d915
/dev/sde1      ext4     Z2        /mnt/Z2            9d35eaae-983f-4eba-abc9-434ecd4da09c
/dev/sdf1      ext4     Y1        /mnt/Y1            e2ec37a9-0689-46a8-a07b-0609ce2b7ea2
/dev/sdg1      ext4     Z1        /mnt/Z1            9fa239c1-720f-42e0-8aed-39cf53a743ed
/dev/sdj1      ext4     RAPT      (not mounted)      a9ed7ecb-96ce-40fe-92fa-e07a532ed157
/dev/sdj2      swap               <swap>             20826c74-eb6d-46f8-84d8-69b933a4bf3f

Or to find this information with non-root privileges, use:

$ lsblk -o name,kname,uuid
NAME                     KNAME UUID
sda                      sda   
├─sda1                   sda1  A103-2001
└─sda2                   sda2  6i2E71-zJzL-KXuG-juYv-mbNY-kROA-XsIPlm
  ├─vg0-var (dm-0)       dm-0  cebi84r5-0401-491e-a0d6-de0j3bnw867c
  ├─vg0-home (dm-1)      dm-1  cceguid6-f3mc-4d7a-a1f2-83f2mkpds3q1
  └─vg0-root (dm-2)      dm-2  973ed4rf-6611-47ed-877c-b66yhn5tgbc7
sdb                      sdb   
└─sdb1                   sdb1  j1Pr1X-b0uM-bkWZ-KNYQ-gezL-YliV-ScRufFyD
  └─vg0-home (dm-1)      dm-1  cefmkbe6-f4n8-4d7a-al32-83f259ijn6t7
sr0                      sr0   


At this point you should see a list of your system drives and a long strings of characters. These long strings are the UUIDs.

  • Now connect your USB device and wait for a few seconds . . .
  • Reexecute blkid -o list -c /dev/null

Notice a new device and UUID? That is your USB storage.

Tip: If blkid does not work as expected, You can look for the UUIDs in /dev/disk/by-uuid/:
$ ls -lF /dev/disk/by-uuid/

Mounting USB memory

You need to create the directory in which you are going to mount the device:

# mkdir /mnt/usbstick
As root

Mount the device as root with this command (do not forget to replace device_node by the path you found):

# mount device_node /mnt/usbstick

or

# mount -U UUID /mnt/usbstick

If mount does not recognize the format of the device you can try to use the -t argument, see man mount for details.

Note: If mounting your stick does not work you can try to repartition it, see Format a device.
As normal user with mount

If you want non-root users to be able to write to the USB stick, you can issue the following command:

# mount -o gid=users,fmask=113,dmask=002 /dev/sda1 /mnt/usbstick
As normal user with fstab

If you want non-root users to be able to mount a USB memory stick via fstab, add the following line to your /etc/fstab file:

/dev/sda1 /mnt/usbstick vfat user,noauto,noatime,flush 0 0

or better:

UUID=E8F1-5438 /mnt/usbstick vfat user,noauto,noatime,flush 0 0

(see description of user and other options in the main article)

Note: Where /dev/sda1 is replaced with the path to your own usbstick, see Mounting USB memory.

Now, any user can mount it with:

$ mount /mnt/usbstick

And unmount it with:

$ umount /mnt/usbstick
Poor copy performance to USB pendrive

If you experienced slow copy speed to pendrive (mainly in KDE), then append these three lines in a systemd tmpfile:

/etc/tmpfiles.d/local.conf
w /sys/kernel/mm/transparent_hugepage/enabled - - - - madvise
w /sys/kernel/mm/transparent_hugepage/defrag - - - - madvise
w /sys/kernel/mm/transparent_hugepage/khugepaged/defrag - - - - 0

And paste these at the end of your /etc/sysctl.conf:

kernel.shmmax=134217728
vm.dirty_background_bytes = 4194304
vm.dirty_bytes = 4194304

Reboot. This also reduces the freezes of the KDE's panel.

Mount to /media

If you don't like your removable drives automounting into /var/run/$USER, try creating a udev rule like this:

/etc/udev/rules.d/99-udisks2.rules
ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{UDISKS_FILESYSTEM_SHARED}="1"

I found that I had to reboot for the change to take effect, although allegedly running this should work:

$ udevadm control --reload