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My HDD mountpoint was at /mnt/old, now I changed it to /mnt/new

So for seamless transition now /mnt/old is a symlink to /mnt/new.

Gradually I want all the programs to use the new mountpoint. How can I monitor what programs access the old path (currently symlink)?

fanotify doesn't work, it resolves the final path, so monitors /mnt/new.

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  • fanotify_mark(2) tells about a flag FAN_MARK_DONT_FOLLOW to not follow symlinks. Maybe the tool you are using could benefit from this?
    – A.B
    Jul 18, 2021 at 10:49
  • seems like it doesn't register any events then (working with /mnt/old, if I specify /mnt/old/ then it's like before)
    – asd
    Jul 18, 2021 at 11:04
  • Does it work if you make /mnt/old a bind mount instead of a symlink to /mnt/new? Or export /mnt/new via nfs and mount it from the same machine on /mnt/old? (I'm not able to test any of those right now)
    – user313992
    Jul 18, 2021 at 14:50

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You can use one of Brendan Gregg's perf-tools, namely opensnoop, which is an ftrace script to monitor for files of a given name (a regular expression) being opened. For an ls command you would get output something like

$ sudo opensnoop /mnt/old
COMM             PID      FD FILE
ls               9263    0x3 /mnt/old

There are many other remarkable performance analysis tools based on Linux perf and ftrace in the set.

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