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How do I get a list of:

  • Pathnames currently being watched by inotify, and
  • PID of the process watching

I ask because I have found that syncthing's inotify watches were preventing my disk from being unmounted.

As can be seen below, nothing appears in lsof or fuser listings.

I guessed well with syncthing... How do I remove the guesswork in future if a disk won't unmount due to inotify?

# umount /media/backup umount: /media/backup: target is busy. # lsof +f -- /media/backup/ # echo $? 1 # fuser -vmM /media/backup/ USER PID ACCESS COMMAND /media/backup: root kernel mount /media/backup # systemctl stop syncthing@ravi # umount /media/backup # echo $? 0
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    Relevant: Who's consuming my inotify resources? Commented Aug 18, 2017 at 8:08
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    From my reading of that, it's possible to know which processes have inotify watches, but not what they are watching. I hope to be wrong! Commented Aug 18, 2017 at 8:11
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    That’s my impression too. Either way, once this question is answered it would be worth updating How do I find out which processes are preventing unmounting of a device? Commented Aug 18, 2017 at 8:23
  • @StephenKitt I've done that here, trying to collate all the relevant infomation into a single answer. Let me know if I've missed anything. Commented Aug 20, 2017 at 12:13

2 Answers 2

Reset to default
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Maybe the fdinfo for the fd of the watch can be useful:

$ readlink /proc/$(pgrep inotify)/fd/3 anon_inode:inotify $ cat /proc/$(pgrep inotify)/fdinfo/3 pos: 0 flags: 00 mnt_id: 11 inotify wd:1 ino:357a sdev:700000 mask:fff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7a35000000000000

The sdev seems to be the major:minor device number combination, as seen in the output of lsblk, for example:

$ lsblk | grep 7 loop0 7:0 0 80.5M 1 loop /snap/core/2462

(I was indeed monitoring /snap/core/2462.)

For my /dev/sda1 which is 8:1, the output looked like so:

pos: 0 flags: 00 mnt_id: 11 inotify wd:1 ino:aae1b sdev:800001 mask:fff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:1bae0a0038e16969

This should be sufficient to find out what's blocking unmounting, even though the specific directories or files being watched aren't listed.

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  • Great lead. Using mnt_id as an index into /proc/[pid]/mountinfo would give the mountpoint directory. How to efficiently perform this check for all processes (irrespective of name)? Commented Aug 18, 2017 at 8:50
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    man proc(5) says sdev: The ID of the device where the target file resides (in hexadecimal). It also explains mnt_id and the mountinfo file. Commented Aug 18, 2017 at 8:59
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(WIP Answer)

Thanks to muru's answer for the kickstart.

Using the information in /proc/[pid]/fdinfo/[fd#]:

Possibly lsof: list only files of a particular type with a_inode.

Too slow as a shell script with all the greping. Perhaps system call interface to /proc information.

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