Written 5 Sep 2026. This is a how-to, not a product card.

Unplug the backup USB safely

Finish disk writes, unmount /mnt/backup, then yank the stick into a drawer. Fixes target is busy. You don't need a NAS.

Haven't copied the house folder yet? Start with a backup of the house folder. Stick still blank or Windows-formatted? That wipe is format a USB stick for the house backup. Prefer leaving the stick plugged in for a weekly timer? Mount it at boot with mount the backup USB automatically, and skip this note on weeks the stick stays in.

Skip if the stick stays plugged in

Some people leave the backup stick in the computer so a weekly job can find it. That is fine when nofail is in fstab and you accept that one bad day can touch both copies. This note is for the drawer habit: copy, unmount, unplug, put the stick somewhere else. Don't yank while rsync is still running.

What this is

Linux keeps writing in the background. A green activity light can lie. sync finishes those writes. umount tells the computer the stick is leaving. After that, the cable can come out. The usual mount point in these notes is /mnt/backup. If you mounted somewhere else, use that path instead.

Step 1: awake, then SSH

Power light. Fan. If it looks asleep, start with is the computer still on?. You need SSH from the couch: SSH from the couch. Connect fails? when SSH won't connect.

Step 2: make sure the copy finished

If you just ran rsync, wait until the prompt comes back. A stuck copy is not a finished backup. Confirm files landed when you care: check that the backup actually copied. Still copying, or the stick vanished mid-job? When the house backup won't run.

Step 3: see that it is mounted

Print the mount line:

findmnt /mnt/backup

A line with /mnt/backup means it is attached. No line means it is already unmounted (or never mounted). You can still run sync and unplug. Stick not listed anywhere? see if the USB backup disk showed up.

Step 4: finish writes, then unmount

Flush pending writes:

sync

Then unmount the backup folder:

sudo umount /mnt/backup

Quiet success prints nothing. Confirm it is gone:

findmnt /mnt/backup

No line is what you want. Fuller look at attached folders: see which folders are already attached. Optional finish-writes note: finish disk writes.

Step 5: if umount says target is busy

Something still has a file open on the stick. Leave that SSH window (or any cd /mnt/backup shell) sitting in another folder:

cd ~

Stop a leftover viewer if you left one open:

pkill -f '/mnt/backup' || true

Then try again:

sync && sudo umount /mnt/backup

Still busy? See who holds it:

sudo lsof +f -- /mnt/backup

Or:

sudo fuser -vm /mnt/backup

Close or kill only what you recognize from that list. Don't force-unmount the system disk. A last-resort lazy unmount (detaches when the last handle closes) is:

sudo umount -l /mnt/backup

Prefer fixing the busy handle over -l when you can. After a clean unmount, yank the stick and put it in a drawer. A problem on this computer cannot also wipe a copy that is sitting somewhere else.

Step 6: next week, mount again (or leave it auto)

Plug the same stick back in. Hand mount the way the backup note taught you, or rely on fstab if you set that up:

sudo mount /mnt/backup

Or, if you still mount by device name from lsblk:

sudo mount /dev/sdb1 /mnt/backup

Swap sdb1 for the partition on your printout. UUID mount at boot is mount the backup USB automatically. Then run the copy again, or let the weekly timer do it: back up the folder every week without remembering.

What this is not

This is not a reason to yank the cable while rsync is still printing. It is not umount of the system disk (/). It is not eject from a Windows laptop (this stick is usually ext4). It is not a NAS. It is not a substitute for confirming the copy landed. It is not forcing umount -l every time so you can ignore a busy shell.

What next

Confirm files landed: check that the backup actually copied. Pull one file back sometime: restore one file from the USB backup. Leave the stick mounted at boot: mount the backup USB automatically. Weekly copy without remembering: back up the folder every week without remembering. Prefer another old PC instead of a stick: copy the house folder to another old computer.

Skip

• Skip yanking while rsync (or any copy) is still running.
• Skip if the stick stays plugged in on purpose for a weekly timer (use auto-mount instead).
• Skip unmounting / or the system disk.
• Skip buying a NAS so a stick can unmount cleanly.
• Skip force-unmount as the first move. Leave the busy folder and try again.
• Skip cloud backup until a plain second copy exists on a stick or another old PC.