A question about fsck and the -t option

Ronald F. Guilmette rfg at tristatelogic.com
Wed Apr 2 08:43:26 UTC 2014

If fsck is invoked upon a /dev device node which is a hard disk
partition containing a valid file system, and if this invocation
of fcsk _does not_ include any -t or -T options, then does fsck
make any sort of attempt to automagically determine or intuit what
sort of file system exists upon and within the given partition?

Previous to today, I had always believed that either (a) fsck looked
at the magic number in the first word of the partition in order to
automagically determine the file system type or else (b) that fsck,
on FreeBSD at least, defaulted (in the absence of any explicit -t or
-T options) to assuming that the file system type was ufs.  But as of
this moment it appears to me that neither of these assumptions were or
are true, and that in the absence of all -t and/or -T options, fsck on
FreeBSD simply throws up its hands and says "Could not determine
filesystem type".

Is this the intended outcome in such cases?

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