USB storage devices

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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.

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, no need to open a console.

Otherwise see sections below.

Auto-mounting with udev

See Udev:Auto mounting USB devices

Manual mounting

Note: Before you decide that your Arch Linux does not mount your USB device, be sure to check all available ports. Since some might not share the same controller, and will then not be able to mount 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 | egrep "sd[a-z]"
  • running
# fdisk -l

lists all available partition tables.

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 (ie /dev/sda).

To find the current UUIDs execute:

# 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

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


# mount -U UUID /mnt/usbstick

If mount does not recognized 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:

$ sudo 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 merge this three line to the end of your /etc/rc.local:

echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
echo madvise > /sys/kernel/mm/transparent_hugepage/defrag
echo 0 > /sys/kernel/mm/transparent_hugepage/khugepaged/defrag

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

vm.dirty_background_bytes = 4194304
vm.dirty_bytes = 4194304

And reboot. This also reduces the freezes of the KDE's panel.