I'm trying to unmount a backup filesystem that I don't need anymore. When I run the "umount" command, system says:

umount: /backup: target is busy

And following commands does not work and same reason (busy) returns to me:

fuser -cuk /backup
fuser -k -9 /backup
umount -f /backup
mount -o remount /backup; umount /backup


lsof |grep /backup | grep -v "backup.log"

command returns nothing already. (grep -v is because ignore backup.log files. If I'm wrong I can change.)

Why I cannot umount this filesystem and how can I do?


Commands those are I tried and outputs of them:

myserver:~ # fuser -cuk /backup
myserver:~ # fuser -k -9 /backup
myserver:~ # umount -f /backup
umount: /backup: target is busy
    (In some cases useful info about processes that
     use the device is found by lsof(8) or fuser(1).)
myserver:~ # mount -o remount /backup; umount /backup
umount: /backup: target is busy
    (In some cases useful info about processes that
     use the device is found by lsof(8) or fuser(1).)
myserver:~ #

OS Version:

myserver:~ # cat /etc/os-release
PRETTY_NAME="SUSE Linux Enterprise Server for SAP Applications 12 SP2"

And when I check the I/O with "iostat" command I see the physical disk (/dev/sdx) that mounted to this filesystem, there are reading but no writing.

Mounted list:

myserver:~ # mount | grep backup
/dev/mapper/vgbackup-lvbackup on /backup type xfs (rw,relatime,attr2,inode64,noquota)
  • yes. none of them works. How can I check respawned processes? If there is one of them, how can't I see this processes or open files? It's so weird. – Gefolge Dec 24 '18 at 10:23
  • One thing that doesn't show in lsof is mount points. So, if you have mounted something to a directory in that filesystem, or mounted a file from that FS somewhere else (mount -o loop ...) they won't show in lsof but prevent umounting. – xenoid Dec 24 '18 at 10:36
  • I cannot see anything that mounted to /backup or under of /backup at neither fstab nor df -h command. – Gefolge Dec 24 '18 at 10:52
  • my question format has been broken :) it doesn't show code blocks. I'm so lucky today. (ok that was my fault. i fixed it.) – Gefolge Dec 24 '18 at 11:08

There's this question on Linux & Unix SE: umount: device is busy. Why?

Few answers:

  1. It seems the cause for my issue was the nfs-kernel-server was exporting the directory. The nfs-kernel-server probably goes behind the normal open files and thus is not listed by lsof and fuser.

    When I stopped the nfs-kernel-server I could umount the directory.

  2. the cause for my manifestation of this problem just now was a stale loopback mount. I'd already checked the output of fuser -vm <mountpoint>/lsof +D <mountpoint>, mount and cat /proc/mounts, checked whether some old nfs-kernel-server was running, turned off quotas, attempted (but failed) a umount -f <mountpoint> and all but resigned myself to abandoning 924 days' uptime before finally checking the output of losetup and finding two stale configured-but-not-mounted loopbacks

  3. For me, the offending process was a daemon running in a chroot. Because it was in a chroot, lsof and fuser wouldn't find it.

    If you suspect you have something left running in a chroot, sudo ls -l /proc/*/root | grep chroot will find the culprit (replace "chroot" with the path to the chroot).

  4. Anonymous inodes


    These are the most elusive type of pokemon, and appear in lsof's TYPE column as a_inode (which is undocumented in the lsof man page).

    They won't appear in lsof +f -- /dev/<device>, so you'll need to:

    lsof | grep a_inode

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