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Overlayfs mounts silently ignore bind mounts from the lowerdir #3543

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Lindenk opened this issue Apr 23, 2025 · 3 comments
Open

Overlayfs mounts silently ignore bind mounts from the lowerdir #3543

Lindenk opened this issue Apr 23, 2025 · 3 comments

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@Lindenk
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Lindenk commented Apr 23, 2025

It looks like if a directory is has bind mounted children, they are silently ignored when the directory is used as a lowerdir in an overlayfs mount

Here's a minimal example:

mkdir a b b/z c d workdir
touch a/1 b/2 c/3
mount -o bind a b/z
mount -t overlay overlay -o lowerdir=b,upperdir=c,workdir=workdir d
ls d # returns "2 3 z" as expected
ls d/z # empty instead of "1" as expected. It isn't reading from "a"
@Lindenk Lindenk changed the title Overlayfs mounts silently ignore bind mounts from the lowerdir Overlayfs mounts silently ignores bind mounts from the lowerdir Apr 23, 2025
@Lindenk Lindenk changed the title Overlayfs mounts silently ignores bind mounts from the lowerdir Overlayfs mounts silently ignore bind mounts from the lowerdir Apr 23, 2025
@echoechoin
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echoechoin commented Apr 24, 2025 •
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reference:
https://unix.stackexchange.com/questions/547232/how-to-mount-overlayfs-where-lower-has-child-mounts
https://superuser.com/questions/1849769/overlayfs-hide-lower-overlay

@karelzak
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I have doubts that this is a mount(8) issue; you need to discuss it with Linux kernel developers. mount(8) just sends the options to the kernel and does not interpret them.

@RushingAlien
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overlayfs just doesn't share submounts of a lowerdir, this is behaviour from the kernel.

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@karelzak @Lindenk @echoechoin @RushingAlien