I can't unmount a disk because something's using it. How do I find what?
Aug 11, 2026
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by John Britto
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1 min read
Quick Linux Tip #21 :
Try: sudo lsof +D /mnt/backup
Info: Lists all active processes holding open files under a specific directory to identify unmount blockers.
Examples:
$ sudo lsof +D /mnt/usb
$ sudo fuser -m /var/log # List processes using filesystem
$ sudo fuser -k -SIGTERM /mnt/backup # Graceful kill first
Note: +D recurses subdirectories. fuser -k sends SIGKILL by default; always try passing -SIGTERM first to allow processes to close gracefully.
LinuxTeck.com
linuxteck@ubuntu:~$ sudo lsof +D /mnt/backup
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
bash 3456 linuxteck cwd DIR 8,1 4096 524290 /mnt/backup
vim 4567 linuxteck 4u REG 8,1 12345 524301 /mnt/backup/notes.txt
rsync 5678 root 3w REG 8,1 45678901 524325 /mnt/backup/data.tar
linuxteck@ubuntu:~$ sudo fuser -km /mnt/backup
/mnt/backup: 3456c 4567c 5678c
linuxteck@ubuntu:~$
About John Britto
John Britto Founder & Chief-Editor @LinuxTeck. A Computer Geek and Linux Intellectual having more than 20+ years of experience in Linux and Open Source technologies.
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