Подскажите документацию по командам troff

Все ссылки в Google фиолетовые. Везде написано что это, команд нигде нет.
Фрагмент:
\fBfsck\fP normally does not check whether the device actually exists before calling a filesystem specific checker. Therefore non\-existing devices may cause the system to enter filesystem repair mode during boot if the filesystem specific checker returns a fatal error. The \fI/etc/fstab\fP mount option \fBnofail\fP may be used to have \fBfsck\fP skip non\-existing devices. \fBfsck\fP also skips non\-existing devices that have the special filesystem type \fBauto\fP.
.RE
.sp
\fB\-C\fP \fIfd\fP
.RS 4
Display completion/progress bars for those filesystem checkers (currently only for ext[234]) which support them. \fBfsck\fP will manage the filesystem checkers so that only one of them will display a progress bar at a time. GUI front\-ends may specify a file descriptor \fIfd\fP, in which case the progress bar information will be sent to that file descriptor.
.RE
.sp
\fB\-M\fP