Score:1

Ubuntu

"Invalid cross-device link" hard for directories on the same filesystem

Bill

11/7/23, 7:43 PM

I know hard links can't cross filesystems, but trying to link files via bind mounts that physically live on the same filesystem fails as well. I detailed things below to visualize it better, but the TLDR of my question is why is ln treating the mounted directories as though they live separately?

Basically, copying files into a share folder would be best-served with hardlinks so I'm not duplicating space:


mymedia/
├─ share/
│  ├─ pics/
│  │  ├─ pic2.tif
│  ├─ vids/
│  │  ├─ vid1.mov
├─ homevid/
│  ├─ vid1.mov
│  ├─ vid2.mov
│  ├─ vid3.mov
├─ homepic/
│  ├─ pic1.tif
│  ├─ pic2.tif
├─ training/

mymedia/share is on one drive (Media1), whereas homepic is on Media2 and homevid on Media3. The two folders in share are mounted from Media2/Media3. This is from fstab:

/dev/disk/by-uuid/UUID_1 /mnt/Media1 auto 0 0  
/dev/disk/by-uuid/UUID_2 /mnt/Media2 auto 0 0  
/dev/disk/by-uuid/UUID_3 /mnt/Media3 auto 0 0  
/mnt/Media1 /mnt/mymedia none bind 
/mnt/Media2/homepic /mnt/mymedia/homepic none bind
/mnt/Media2/share /mnt/mymedia/share/pics none bind
/mnt/Media3/homevid /mnt/mymedia/homevid none bind
/mnt/Media3/share /mnt/mymedia/share/vids none bind

I can create the link while using the "real" path, like so: ln /mnt/Media2/homepic/pic2.tif /mnt/Media2/share/, and see the new file in both directories; stat confirms the inode is the same for the files, as well as same device:

Path	Device
/mnt/Media2/homepic	831h/2097d
/mnt/Media2/share	831h/2097d
/mnt/mymedia/homepic	831h/2097d
/mnt/mymedia/share/pics	831h/2097d
/mnt/mymedia/training	821h/2081d

Unfortunately, using the bind mounts would be way better for my workflow (this fails): ln /mnt/mymedia/homepic/pic1.tif /mnt/mymedia/share/pics/pic2.tif

What am I missing?

1740

0 + 10

command-line

partitioning

hard-link

Hi-Angel

11/7/23, 10:55 PM

You seem to have error in your fstab: you bind-mount both `Media2` and `Media3` to the same directory `/mnt/mymedia/share/pics`. If I understood correctly, these are different devices. Even if not, it doesn't make sense to have them bind-mounted to the same dir. And I guess that leads to the `ln` error you're seeing.

Bill

11/9/23, 12:48 PM

Thanks for pointing that out; that was a transcription error on my part and I edited the post. The `vids` and `pics` folders in `mymedia/share` each live on Media3/2. Maybe I still have an error though that I'm not catching, unless it has something to do with the parent (`mymedia/share`) living on Media1?

mook765

11/9/23, 1:10 PM

`/dev/sda1 /mnt/Media1 /mnt/mymedia none bind` doesn't look like a valid fstab line. `/dev/sdb1 /mnt/Media2 none bind` is not a bind mount, your are mounting a device here, same for `/dev/sdc1 /mnt/Media3 none bind`. Device names like `/dev/sda1` should be avoided, use UUID or file-system labels to identify correct partitions.

Hi-Angel

11/9/23, 3:44 PM

Can you please confirm if `df /mnt/mymedia/homepic/pic1.tif /mnt/mymedia/share/pics/` *(that is, `df` command over the parameters that make `ln` fail, except the second one is a dir, not a filename which wasn't created)* shows the same device for both arguments?

Bill

11/10/23, 12:41 AM

@Hi-Angel: it returns that they're on the same device: ```lang-bash $ df /mnt/mymedia/homepic/pic1.tif /mnt/mymedia/share/pics/ Filesystem 1K-blocks Used Available Use% Mounted on /dev/sdb1 13563485152 9514471848 3365377900 74% /mnt/mymedia/homepic/ /dev/sdb1 13563485152 9514471848 3365377900 74% /mnt/mymedia/share/pics/ ``` I guess I'm not sure whether to be thrilled or not! :) **EDIT:** My triple-backticks are getting garbled. Sorry!

Bill

11/10/23, 12:43 AM

@mook765 - You're right, it's not; that was another mistake of mine typing absent coffee. I updated by UUID and remounted. This should look more proper hopefully: ```lang-bash /dev/disk/by-uuid/UUID_1 /mnt/Media1 auto nosuid,nodev,nofail,x-gvfs-show,x-gvfs-name=Media1 0 0 /dev/disk/by-uuid/UUID_2 /mnt/Media2 auto nosuid,nodev,nofail,x-gvfs-show,x-gvfs-name=Media2 0 0 /mnt/Media1 /mnt/mymedia none bind /mnt/Media2/share /mnt/mymedia/share/pics none bind /mnt/Media2/homepic /mnt/mymedia/homepic none bind``` **EDIT:** My triple-backticks are getting garbled. Sorry!

mook765

11/10/23, 2:31 AM

The fstab you provide here is still a mess, take a look at the third line: `/mnt/mymedia/share none bind ` is not a valid fstab line. Also now I don't see drive `Media1` mounted anywhere anymore.

Hi-Angel

11/10/23, 6:00 AM

Apparently, [it is a deliberate feature](https://unix.stackexchange.com/a/380033/59928). The answer there refers to [this discussion](https://lists.archive.carbon60.com/linux/kernel/855705#855705), I don't fully understand the reasoning in the quoted email, but apparently it is a case of "never ever break userspace" kernel rule. Reflinks just happen to not work across bind-mounts on the same device, and apparently that feature became used in apps like Podman/Docker for containerization purposes *(it's just my theory from the comment)*, so one can't "undo" that behavior.

mook765

11/10/23, 8:20 AM

https://stackoverflow.com/a/55387608

Bill

11/11/23, 6:13 PM

@mook765: The Media1 line wasn't rendering while on same line as the backticks; fixed it. if I'm reading your and @Hi-Angel's links correctly, Even though `/mnt/mymedia/share/pics` and `/mnt/Media2/share` live alongside each other, `ln` considers them different because the parent `/mnt/mymedia/share` lives on `/mnt/Media1`? Or could it (unlikely) be related to the directories living so close to `/mnt`?

Elon Musk

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EN: "Invalid cross-device link" hard for directories on the same filesystem

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