.CD "fsck, fsck1 \(en perform file system consistency check"
.SX "fsck\fR [\fB\(enaclmrs\fR]\fR [\fIdevice\fR] ..."
.FL "\(ena" "Automatically repair inconsistencies"
.FL "\(enc" "Check and list only the specified i-nodes
.FL "\(enl" "List the files and directories in the filesytem
.FL "\(enr" "Prompt user for repairs if inconsistencies are found
.FL "\(ens" "List the superblock of the file system"
.EX "fsck /dev/hd4" "Check file system on \fI/dev/hd4\fR"
.EX "fsck \(ena /dev/at0" "Automatically fix errors on \fI/dev/at0\fR"
.EX "fsck \(enl /dev/fd0" "List the contents of \fI/dev/fd0\fR"
.EX "fsck \(enc 2 3 /dev/hd3" "Check and list \fI/dev/hd3\fR i-nodes 2 & 3"
.PP
\fIFsck\fR performs consistency checks on the file systems which reside 
on the specified devices.
\fIFsck1\fR is an alternate version for use on obsolete V1 file systems.
When either the \fB\(ena\fR or \fB\(enr\fR flags are given, the file system
will be repaired if errors are found.
Before running \fIfsck\fR on a mounted file system, it must first be unmounted.
Trying to repair a mounted file system is dangerous and should not be 
attempted.
.PP
To repair the root file system (which cannot be unmounted), first 
hit the F1 key to find the pid of the \fI/etc/update\fR process.
Then become superuser and send \fIupdate\fR signal 9 using \fIkill\fR.
After doing this, hit F1 again to verify that \fI/etc/update\fR has vanished.
Next run \fIfsck\fR and then immediately reboot
the computer, WITHOUT doing a \fIsync\fR.
.PP
This is the only situation in which you can (in fact, must) reboot without
doing a \fIsync\fR.
Rebooting is needed because \fIfsck\fR repairs the disk but does not affect
the (possibly incorrect) information held in memory.
Doing a \fIsync\fR would force the (possibly incorrect) information from
memory back onto the disk, thus ruining the work done by \fIfsck\fR.
By rebooting immediately, memory is reloaded with correct information from the
disk.
It is necessary to kill \fI/etc/update\fR before repairing the root file system
to prevent it from issuing \fIsync\fR calls while \fIfsck\fR is running.
Because \fI/etc/update\fR only affects mounted file systems (and the root),
when repairing a nonroot file system, unmounting it is sufficient; it is not
necessary to kill \fI/etc/update\fR.



.SP 1