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  • Thanks ! How do I determine a given path is virtual ? In this case, /sys/devices/... ? Commented Dec 8, 2021 at 15:28
  • I think, in general, you can't, because there's a potentially infinite amount of file systems, and there's no clear distinction what is a "virtual" and a "normal" file system (is overlayfs virtual? What about tmpfs? How is a bind mount counted?…). But if you want to know on a "normal" system, you just check what mount a path is under, and check whether the file system there is among the "well-known" "regular storage" file systems (ext2/3/4, xfs, btrfs, reiserfs, zfs, vfat, exfat, ntfs, hfs, nfs, cifs, squashfs, iso9669, …). Commented Dec 8, 2021 at 15:47
  • generally, even more, your question is "how can I make sure I can create a file on a file system": and guess what, you can't create a file on a read-only file system, even if it's 100% backed by a storage device, and you can't create a file on a file system where you don't have permission to do so, or on a network filesystem if the server doesn't feel like it today, and you can't create a file on a file system that's full, and you can't create a file on a file system if SELinux decides that you're a rogue process, and … so, "virtual" is really not your problem. Just check whether you can. Commented Dec 8, 2021 at 15:49
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    @Veverke you need to determine what the closest mount point is, and then the corresponding file system type, and look it up in /proc/filesystems. If the relevant line in /proc/filesystems says nodev, then it is a virtual file system. Some virtual file systems do allow arbitrary storage (e.g. tmpfs and network file systems) but most don’t. Commented Dec 8, 2021 at 15:55
  • Let me rephrase that slightly; nodev means it doesn’t have a local backing device, so it’s either a network file system, a RAM-base file system, or some sort of virtual file system. Commented Dec 8, 2021 at 18:31