Re: /mnt usage

[David Wright <deblis@lionunicorn.co.uk>]

On Mon 15 Jan 2024 at 21:41:15 (-0800), David Christensen wrote:
> On 1/15/24 20:05, David Wright wrote:
> > And I've never created any mount point under /mnt. For a one time
> > copy, /mnt is handy; always there, I don't have to mkdir at all.
> 
> What about when you have an portable backup drive that you connect
> once a week?  And the drive is encrypted?  And your backup system
> wants to know where?

I plug it in, udev springs into action, and mount points for all
the partitions are created under /media with appropriate names.

The lookup "table" is a set of files under /etc/udev/rules.d/my-mountpoints
where each filename is any string that will only be seen from the new
device or partition, and its content is the name for the mountpoint.
For a partition, the string can be any of:

  # ID_FS_LABEL              for my conventional drives, USB sticks, SD cards, etc
  # ID_FS_UUID               for FAT and encrypted partitions, but try to make this a legacy option
  # ID_SERIAL_SHORT          for DVD drives, NTFS, and certain other formats
  # ID_PART_ENTRY_NAME       for encrypted partitions on GPT
  # (basename of) DEVNAME    for unrecognised sticks, cards, etc
  # ID_SERIAL                for DVD drives, NTFS, and certain other formats
  # quit after any success.¹

When udev sees a device, a string matching:

  # properties are, in order:
  # ID_SERIAL_SHORT
  # ID_SERIAL
  # quit after any success.

will create a device (typically cdromN, where N depends on which
device) if inserting a data CD or DVD, but also create a symlink
(by stripping off N).

There are currently 59 entries to select from, and the setup is
very flexible. For example, I have a dead USB stick with the
serial number A400000000000215 that creates a "mountpoint" called
"/media/. PLAY CD". If you place a Red Book CD into one particular
PC and insert that stick, the CD drawer closes and the CD plays.
The player has a 3.5mm socket connected to a HiFi system.
The PC just has to be running for this trick to work, because
a @reboot root cron job is watching /media with inotifywait.
No one has to be logged in, or /home even unlocked.
Pull the stick out and the CD drawer opens again.

> What about when you need multiple temporary mount points?

I can only think of one or two occasions when I use /mnt at all:
the obvious case, a "foreign"/brand-new stick; but also when
I install a new system, I use /mnt for a USB stick that runs
a huge initial install/configure script, which includes
bootstrapping the setup I've just described above.

In your parlance, my accessories are all pets, not cattle.

¹ comments from the rules script.

Cheers,
David.