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I'm curious if someone could explain to me what causes the odd scenario where we have a duplicate mount that appears cyclical on Centos 7 when binding a nfs directory?

In our hosting environment we chroot our users and in order to provide case specific access to some users we bind mount into external nfs directory.

If we mount multiple times we always end up with two seemingly identical mounts to the target with the only difference being one appears to be cyclical pointing to itself(?).

Both are active and show the same content and it doesn't appear to be a "ghost" directory.

Info to replicate:

fstab entries:

www:/protected /protected nfs defaults,_netdev,rw,mountproto=tcp 0 0
/protected/dir1 /$accthome/dir1 none defaults,bind,x-systemd.requires=/protected 0 0

df output looks good pre and post mounting with a single entry

www:/protected/dir1    504G 104G 375G  22% /$accthome/dir1

findmnt and mount both show a single entry

├─/protected/dir1           www:/$accthome/dir1    nfs

and

www:/protected/dir1 on $accthome/dir1 type nfs

Run mount -a again and I end up with still a single df entry but duplicates in the findmnt and mount output. The only difference being in findmnt it looks to be a submount of the initial mount?

├─/protected/dir1                    www:/$accthome/dir1    nfs
│ └─/protected/dir1                  www:/$accthome/dir1    nfs 

and

www:/protected/dir1 on $accthome/dir1 type nfs
www:/protected/dir1 on $accthome/dir1 type nfs

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