Written 1 Sep 2026. This is a how-to, not a product card. Buy links are not tagged yet.

See which leftover-box folders are already attached

After you can list disks with lsblk (and before you blame a missing USB backup), use findmnt to see which folders are already attached (mounted) so you know what is live as / or a USB path.

A disk name from lsblk is not the same as a leftover-box folder you can open. Mount means the leftover box made a disk slice show up as a folder path. Tonight you only want the map: which leftover-box paths are already live. You do not need a disk app, a format step, or a shopping cart for this look.

Skip until SSH works

If you cannot log in from the couch yet, stop. That is SSH from the couch. Mount maps do not help a login that fails.

If you only need the list of disks and USB sticks, that is see disks and USB sticks on the leftover box (lsblk). If you only need room left on a path, that is see if the leftover box still has room (df). If you only need whether a USB stick showed up as a device name, that is see if the USB backup disk showed up.

What this is

findmnt lists mounted filesystems: leftover-box folder paths already attached, plus where each one came from. In plain English: which leftover-box folders are live right now. Mount means that attachment — a disk slice showing up as a path like / or /media/…. Night one is a look. findmnt does not mount, unmount, format, or wipe anything.

Practice: see what is already attached

SSH in from the couch, then ask:

findmnt

You should see a tree or table. In plain English:

TARGET — the folder path that is live (often / for the main system).
SOURCE — which disk slice feeds that path (a name like /dev/sda1 or similar).
FSTYPE — the filesystem flavor on that slice (ext4, xfs, vfat, and so on).
OPTIONS — how it is attached (read-write, and other flags). Night one, you mostly ignore the long option string.

Point at the row whose target is /. That is the live root of the leftover-box system. A USB path, when it is attached, often shows under /media/ or /mnt/. Home-safe look only. Do not unmount or remount anything tonight.

Optional: narrow to common disk flavors:

findmnt -t ext4,xfs,btrfs,vfat,exfat,ntfs

Same idea, fewer rows — useful when the full list feels noisy. Still a look.

Optional: ask about one path only:

findmnt /

That prints how / is attached. Still no change to the disk.

Optional: after you plug in a USB for backup

Plug the stick into the leftover box. Run lsblk so you see the device name, then run findmnt again. If the stick is already attached, you will see a leftover-box target path for it. If you only see the device in lsblk and no path in findmnt, the stick is plugged in but not showing as a leftover-box folder yet — do not make mounting tonight's job. The backup job, once a path is live, is a backup of the leftover-box folder.

Useful extras, still a look

Skip mount and umount as the job. Night one is the map of what is already attached.

Skip rewriting disks, dd, shred, fdisk, parted, or format as the lesson. Those are not this note.

Skip buying a NAS because a leftover-box path looks small. Free room is leftover-box disk-space. Disk names without the mount map are leftover-box lsblk.

Skip screen, tmux, and port 22 forwarding. Keep SSH on the house network: keep the leftover box on the house network.

Skip awk, sed, and install as new pages this cycle.

What this is not

This is not leftover-box lsblk. That lists disks and USB sticks by name: see disks and USB sticks on the leftover box. It is not leftover-box disk-space (df). That shows how full a mounted path is: see if the leftover box still has room. It is not leftover-box disk, which focuses on how big the main disk already is: see how big the leftover box disk already is. It is not leftover-box USB-disk, a shorter “did the stick show up?” check: see if the USB backup disk showed up. It is not the backup copy itself: a backup of the leftover-box folder.

What next

Need the disk-name list first? See disks and USB sticks on the leftover box. Need labels, UUIDs, and filesystem types on a slice? Read leftover-box disk labels and UUIDs. Need room left on a path? See if the leftover box still has room. Stick visible and ready for a second copy? A backup of the leftover-box folder. Need how big the main disk already is? See how big the leftover box disk already is. Keep SSH on the house network: keep the leftover box on the house network. Leftover-box-awk, leftover-box-sed, and leftover-box-install stay deferred this cycle.

Skip

Skip if SSH still fails. Finish SSH from the couch first.
Skip leftover-box lsblk, leftover-box disk-space, or total disk size as tonight's job if you only came for the mount map. Those notes already exist.
Skip mount/umount as the lesson, and skip rewriting disks, dd, shred, fdisk, parted, and format.
Skip buying a NAS because a path looks small.
Skip awk/sed/install as new pages this cycle, screen, tmux, and port 22 forwarding.
Skip opening SSH to the internet. That is keep the leftover box on the house network. Do not forward port 22.

Sources

Debian: findmnt(8). Ubuntu: findmnt(8). Part of util-linux. Official pages only. For the disk-name list, see see disks and USB sticks on the leftover box. For free room, see see if the leftover box still has room. For a second copy once a USB path is live, see a backup of the leftover-box folder. For the login, see SSH from the couch.

Also on this topic

SSH from the couchType commands on the leftover box from your laptop, on the house network. Password login first. Do not open this to the internet. See disks and USB sticks on the leftover boxAfter SSH works (and before you blame a missing USB backup), list disks and USB sticks with lsblk so you see names like sda and sdb without opening a disk app. See if the leftover box still has roomAfter the house folder is working, check that the leftover box is not filling up. Photos stop copying when the disk is full. You do not need a NAS for this look. See how big the leftover box disk already isBefore you buy a tiny computer or a NAS, check how big the leftover box disk already is. See if the USB backup disk showed upBefore you trust the weekly copy, confirm the leftover box can see the USB disk. A backup of the leftover-box folderA second copy of the house folder, on a USB disk you already have, or on another leftover computer. You do not need a NAS for this. Keep the leftover box on the house networkSSH and Pi-hole belong on the house network. Skip this if you never opened the router settings. Do not forward port 22.