fstyp allows the user to determine the file system type of unmounted file systems using heuristic programs.

An fstyp module for each file system type to be checked is executed; each of these modules applies an appropriate heuristic to determine whether the supplied special file is of the type for which it checks. If it is, the program prints on standard output the usual file system identifier for that type (for example, ``ufs'') and exits with a return code of 0; if none of the modules succeed, the error message unknown_fstyp (no matches) is returned and the exit status is 1. If more than one module succeeds, the error message unknown_fstyp (multiple matches) is returned and the exit status is 2.

-v

Produce verbose output. This is usually information about the file systems superblock and varies across different FSTypes. See fs_ufs(4), mkfs_ufs(1M), and tunefs(1M) for details.

See largefile(5) for the description of the behavior of fstyp when encountering files greater than or equal to 2 Gbyte ( 2³¹ bytes).

See attributes(5) for descriptions of the following attributes:

mkfs_ufs(1M), tunefs(1M), fs_ufs(4), attributes(5), largefile(5), hsfs(7FS), pcfs(7FS)

The use of heuristics implies that the result of fstyp is not guaranteed to be accurate.