Whether you call them USB flash disks, memory sticks, keys or drives they are a useful accessory in the world of computers. By now many people will have a collection of various devices of varying capacities. Using them with the Pi is a great way of getting some use out of them rather than letting them gather dust in a drawer.
I tend to transfer files from my Pi using FTP but occasionally it is useful to get stuff onto a USB drive. There are lots of guides already out there but I had a few issues using most of them, mainly due to permission problems. My main goal was to clarify the process by which I could mount standard FAT32 drives and allow the default Pi user read/write permissions.
So here is my procedure for using USB flash drives with the Raspberry Pi where the Pi user has permissions to use it without needing “sudo”. It works great with the shiney new Kingston 32GB DataTraveler I’ve just bought myself.
Step 1 – Plug In The Device
The first step is to plug in your USB stick. If you are using a mouse and keyboard you will need a decent USB hub at this point. (e.g. the PiHub by Pimoroni).
Step 2 – Identify The Devices Unique ID
In order to find the unique reference (UUID) for your drive run the following command in the terminal :
ls -l /dev/disk/by-uuid/
This will give you an output that should list your drive :
The line will usually refer to “/sda” and in this example it is “sda1″. My ID is “18A9-9943″. Note down yours.
You would need to repeat this step if you wanted to use a different device as the UUID would be different.
Step 3 – Create a Mount Point
A mount point is a directory that will point to the contents of your flash drive. Create a suitable folder :
sudo mkdir /media/usb
I’m using “usb” but you can give it whatever name you like. Keep it short as it saves typing later on. Now we need to make sure the Pi user owns this folder :
sudo chown -R pi:pi /media/usb
You will only need to do this step once.
Step 4 – Manually Mount The Drive
To manually mount the drive use the following command :
sudo mount /dev/sda1 /media/usb -o uid=pi,gid=pi
This will mount the drive so that the ordinary Pi user can write to it. Omitting the “-o uid=pi,gid=pi” would mean you could only write to it using “sudo”.
Now you can read, write and delete files using “/media/usb” as a destination or source without needing to use sudo.
Step 5 – Auto Mount
When you restart your Pi your mounts will be lost and you will need to repeat Step 4. If you want your USB drive to be mounted when the system starts you can edit the fstab file :
sudo nano /etc/fstab
Then add the following line at the end :
UUID=18A9-9943 /media/usb auto,users,rw,uid=pi,gid=pi 0 0
My fstab file looks like this :
Make sure you set the correct UUID. Use CTRL-X followed by Y to save and exit the nano editor.
Now reboot :
Your USB drive should be auto-mounted and available as “/media/usb”.
Step 6 – Un-mounting The Drive
You don’t need to manually un-mount if you shutdown your Pi but if you need to remove the drive at any other time you should un-mount it first. Only the user that mounted the drive can un-mount it.
If you used the fstab file to auto-mount it you will need to use :
sudo umount /media/usb
If you are paying attention you will notice the command is “umount” NOT “unmount”!
An Extra Note About File Systems
In the examples above I let the mount command automatically determine the file system of the device. This seems to work ok for me. If you need to you can manually specify the file system by adding the “-t” parameter. For example to specify a FAT32 device you would use :
sudo mount /dev/sda1 /media/usb -o uid=pi,gid=pi -t vfat
If your drive uses NTFS, EXT3 or EXT4 you will need to replace references to “vfat” with “ntfs-3g”, “ext3″ or “ext4″.
If you are using NTFS you will also need to install the following package :
sudo apt-get install ntfs-3g
This technique suits my applications but the main disadvantage is that it is specific to a known USB device given we are using the device ID. However if you created a few mount points in advance you could manually mount a new device to a spare mount point without worrying about updating the fstab file.