问题
Linux: Which process is causing "device busy" when doing umount?
回答1:
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.
回答2:
Just in case... sometimes happens that you are calling umount from the terminal, and your current directory belongs to the mounted filesystem.
回答3:
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).
回答4:
Check for open loop devices mapped to a file on the filesystem with "losetup -a". They wont show up with either lsof or fuser.
回答5:
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.
回答6:
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.
回答7:
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.
回答8:
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..
回答9:
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).
回答10:
Open files
Processes with open files are the usual culprits. Display them:
lsof +f -- <mountpoint or device>
There is an advantage to using /dev/<device> 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 <mountpoint> (see caveat above):
fuser -vmM <mountpoint>
Interactively kill only processes with files open for writing:
fuser -vmMkiw <mountpoint>
After remounting read-only (mount -o remount,ro <mountpoint>), it is safe(r) to kill all remaining processes:
fuser -vmMk <mountpoint>
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 <mountpoint>/
For loopback mounts, also check the output of:
losetup -la
Anonymous inodes (Linux)
Anonymous inodes can be created by:
- Temporary files (
openwithO_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/<device>, so you'll need to:
lsof | grep a_inode
For killing processes holding anonymous inodes, see: List current inotify watches (pathname, PID).
回答11:
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.
回答12:
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'
来源：https://stackoverflow.com/questions/624154/linux-which-process-is-causing-device-busy-when-doing-umount