There is a problem with a USB 3 port on a desktop running Debian.
Until recently, a backup of the system had been regularly performed to
a portable hard drive plugged into the USB 3 port. The drive had been kept permanently plugged into the port and was only mounted when a backup is required.
Then one day the drive could not be mounted. Instead a message of the type 'can't find UUID=' was received. Use of commands such as lsusb,
fdisk -l, lsblk, blkid showed that the kernel does not recognise the hard drive. Use of dmesg suggested that the drive itself might have a hardware problem.
A new portable hard drive and a new flash drive were, in turn, plugged into the USB 3 port, but fdisk -l, lsblk and lsusb outputs suggest that
neither of these devices are recognised by the kernel when in that port.
Someone suggested that the desktop should be unplugged completely
(I.e. at the mains), left for a few minutes and then rebooted.
However, given the uncertainty of the cause of the problem with the port, I am reluctant to shut down the desktop and reboot in case the reboot fails.