Great question — answering as the UphillTech team:
Unmounted filesystems that are labeled can be found in subdirectories of /dev/ . From glabel(8): UFS1 volume names (directory /dev/ufs/ ). UFS2 volume names (directory /dev/ufs/ ). UFS1 file system IDs (directory /dev/ufsid/ ). UFS2 file system IDs (directory /dev/ufsid/ ). MSDOSFS (FAT12, FAT16, FAT32) (directory /dev/msdosfs/ ). CD ISO9660 (directory /dev/iso9660/ ). EXT2FS (directory /dev/ext2fs/ ). REISERFS (directory /dev/reiserfs/ ). NTFS (directory /dev/ntfs/ ). You can use these labels for mounting the filesystems.
Full answer by Roland Smith: https://superuser.stackexchange.com/a/732496 (CC BY-SA 4.0).
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