Linux Which process is causing device busy when doing umount

Question

Linux  Which process is causing  device busy  when doing umount

User · Accepted Answer

Look at the lsof command  list open files  -- it can tell you which processes are holding what open   Sometimes it s tricky but often something as simple as sudo lsof   grep  your device name here  could do it for you

User · Answer

Open files  Processes with open files are the usual culprits  Display them   lsof  f --  lt mountpoint or device gt    There is an advantage to using   dev  lt device gt  rather than  mountpoint  a mountpoint will disappear after an umount -l  or it may be hidden by an overlaid mount   fuser can also be used  but to my mind lsof has a more useful output  However fuser is useful when it comes to killing the processes causing your dramas so you can get on with your life   List files on  lt mountpoint gt   see caveat above    fuser -vmM  lt mountpoint gt    Interactively kill only processes with files open for writing   fuser -vmMkiw  lt mountpoint gt    After remounting read-only  mount -o remount ro  lt mountpoint gt    it is safe r  to kill all remaining processes   fuser -vmMk  lt mountpoint gt    Mountpoints  The culprit can be the kernel itself  Another filesystem mounted on the filesystem you are trying to umount will cause grief  Check with   mount   grep  lt mountpoint gt     For loopback mounts  also check the output of   losetup -la   Anonymous inodes  Linux   Anonymous inodes can be created by    Temporary files  open with O TMPFILE  inotify watches  eventfd   eventpoll   timerfd    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  lt device gt   so you ll need to   lsof   grep a inode   For killing processes holding anonymous inodes  see  List current inotify watches  pathname  PID

User · Answer

Filesystems mounted on the filesystem you re trying to unmount can cause the target is busy error in addition to any files that are in use   For example when you mount -o bind  dev  mnt yourmount dev in order to use chroot there    To find which file systems are mounted on the filesystem run the following   mount   grep   mnt yourmount    To find which files are in use the advice already suggested by others here   lsof   grep   mnt yourmount

User · Answer

If you still can not unmount or remount your device after stopping all services and processes with open files  then there may be a swap file or swap partition keeping your device busy  This will not show up with fuser or lsof  Turn off swapping with   sudo swapoff -a   You could check beforehand and show a summary of any swap partitions or swap files with   swapon -s   or   cat  proc swaps   As an alternative to using the command sudo swapoff -a  you might also be able to disable the swap by stopping a service or systemd unit  For example   sudo systemctl stop dphys-swapfile   or   sudo systemctl stop var-swap swap   In my case  turning off swap was necessary  in addition to stopping any services and processes with files open for writing  so that I could remount my root partition as read only in order to run fsck on my root partition without rebooting  This was necessary on a Raspberry Pi running Raspbian Jessie

User · Answer

lsof and fuser didn t give me anything either   After a process of renaming all possible directories to  old and rebooting the system every time after I made changes I found one particular directory  relating to postfix  that was responsible   It turned out that I had once made a symlink from  var spool postfix to  disk2 pers mail postfix varspool in order to minimise disk writes on an SDCARD-based root filesystem  Sheeva Plug    With this symlink  even after stopping the postfix and dovecot services  both ps aux as well as netstat -tuanp didn t show anything related  I was not able to unmount  disk2 pers   When I removed the symlink and updated the postfix and dovecot config files to point directly to the new dirs on  disk2 pers  I was able to successfully stop the services and unmount the directory   Next time I will look more closely at the output of   ls -lR  var   grep  l   grep disk2   The above command will recursively list all symbolic links in a directory tree  here starting at  var  and filter out those names that point to a specific target mount point  here disk2

User · Answer

Just in case    sometimes happens that you are calling umount from the terminal  and your current directory belongs to the mounted filesystem

User · Answer

Check for open loop devices mapped to a file on the filesystem with  losetup -a   They wont show up with either lsof or fuser

User · Answer

lsof  f --  mountpoint    as lists the processes using files on the mount mounted at  mountpoint  Particularly useful for finding which process es  are using a mounted USB stick or CD DVD

User · Answer

That s exactly why the  fuser -m  mount point  exists   BTW  I don t think  fuser  or  lsof  will indicate when a resource is held by kernel module  although I don t usually have that issue

User · Answer

Also check  etc exports   If you are exporting paths within the mountpoint via NFS  it will give this error when trying to unmount and nothing will show up in fuser or lsof

User · Answer

lsof and fuser are indeed two ways to find the process that keeps a certain file open  If you just want umount to succeed  you should investigate its -f and -l options

User · Answer

You should use the fuser command   Eg  fuser  dev cdrom will return the pid s  of the process using  dev cdrom   If you are trying to unmount  you can kill theses process using the -k switch  see man fuser

[linux] Linux: Which process is causing "device busy" when doing umount?

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