USB drives

(This is part of a larger series on finding your footing on Arch Linux.)

Last modified: 29 May 2022

Goal: Read from and write to external USB drives, including those with the NTFS file system.

References:

• Wiki: USB storage devices
• Wiki: NTFS-3G
• https://wiki.archlinux.org/title/Udisks
• The man pages for lsblk, mount, umount, udisksctl, and udisks

Requirements (depending on the file systems you want to interact with):

• dosfstools
• mtools
• ntfs-3g

These packages allow read/write interaction with the file systems commonly used on USB media.

Manual everything

Well there’s a decent amount going on here. You should roughly grok what a block device is, and what partitions are. You should know what a file system is. You have to mount the USB drive’s filesystem to your computer, so the USB drive’s files are accessible on your system.

• For future reference, run lsblk and remember the output without a USDB connected

• Physically connect USB drive to computer via a USB port

• Run lsblk and identify the drive’s block device and data partition:

  $ lsblk
  

  It takes a little experience to interpret the output. The USB drive’s block device might be sdb. Identify the data partition based on the known disk size—the data partition should take up the majority of the full disk size.

• Create a mount directory inside /mnt to hold the drive’s files. You can name it whatever you want; perhaps use the manufacturer of the drive:

  sudo mkdir /mnt/seagate
  

  You only need to do this step once.

• Mount the drive’s data partition to the mount directory

  sudo mount /dev/sdb2 /mount/seagate
  

  Optionally use lsblk to check that the USB drive is mounted to the just-created mount directory.

• Interact with the files on the USB drive from the /mnt/seagate directory, reading and writing as needed. You’ll need root privileges to write.

• To eject the drive

  umount /mnt/seagate  # by specifying mount point (preferred)
  umount /dev/sdb2     # by specifying device
  
  # Power off
  echo 1 > /sys/block/DISK_NAME/device/delete
  

  From man umount, specifying the mount directory is preferred, in case the physical device is mounted to multiple directories.

  For the power off line see https://unix.stackexchange.com/a/43450 and ArchWiki: USB storage/Device not shutting down after unmounting all partitions

Using udisksctl

Ejecting with udisks2

This package allows you to disconnect power from an e.g. USB drive, which makes for safer ejecting.

Reference:

• man udisksctl and man udisks

• Install the udisks2 package

• Mount drive with umount as above.

• Eject with

  udisksctl unmount -b /dev/sdb2
  

  where the -b flag specifies that /dev/sdb2 refers to a block device. Note that a device partition, e.g. sdb2, is used. Only the device itself, e.g. sdb, is used below with power-off.

• Power off with

  udisksctl power-off -b /dev/sdb
  

  Again, note that udisksctl unmount uses the device’s data partition (e.g. /dev/sdb2) while udisksctl power-off uses the device itself (e.g. /dev/sdb).

File systems

The mount command should detect the USB drive’s file system and use the appropriate library if needed. See e.g. https://wiki.archlinux.org/title/NTFS-3G: the mount command should know to use the ntfs file system after an installation of ntfs-3g.

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