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.Dd February 17, 2003
.Dt FSRESIZE 8
.Sh NAME
.Nm fsresize
.Nd resize an on-disk filesystem
.Sh SYNOPSIS
.Nm
.Ar filesystem
.Ar newsize
.Sh DESCRIPTION
.Nm
resizes a filesystem on disk.
.Ar filesystem
is the name of the disk device where the filesystem resides;
.Ar newsize
is the desired new filesystem size, in sectors.  (Sectors are almost
always 512 bytes, and
.Nm
assumes this.  It will not work correctly for filesystems with other
sector sizes.)
.Nm
can both grow and shrink filesystems.  When growing, the disk device
must of course be large enough to contain the new filesystem;
.Nm
simply extends the filesystem data structures into the new space.  When
shrinking,
.Nm
has to copy anything that currently resides in the space being shrunk
away; there must be enough space free on the filesystem for this to
succeed.  If there isn't,
.Nm
will complain and exit; when this happens, it attempts to always leave
the filesystem in a consistent state, but it is probably a good idea to
check the filesystem with
.Xr fsck 8 .
.Pp
When
.Nm
is applied to a consistent filesystem, it should always produce a
consistent filesystem; if the filesystem is not consistent to start
with,
.Nm
may misbehave, anything from dumping core to completely curdling the
data.  It's probably wise to
.Xr fsck 8
the filesystem before and after, just to be safe.
.Sh WARNING
.\" Remove this when (if) fsck gets fixed.
There is a bug somewhere in fsck; it does not check certain data
structures enough.  A past version of this program had a bug that
produced corrupted rotation layout summary tables, which would panic
the kernel.  This bug is believed fixed, and there are currently no
known bugs in the program.  However, you should be aware that just
because fsck is happy with the filesystem does not mean it is intact.
.Sh EXAMPLES
.Li fsresize /dev/rsd1e 29574
.Sh SEE ALSO
.Xr fs 5 ,
.Xr newfs 8 ,
.Xr fsck 8
.Sh AUTHOR
.Li der Mouse <mouse@rodents.montreal.qc.ca>
A big bug-finding kudos goes to John Kohl for finding the bug referred
to in the WARNING section above.
.Sh BUGS
Can fail to shrink a filesystem when there actually is enough space,
because it does not distinguish between a block allocated as a block
and a block fully occupied by two or more frags.  This is unlikely to
occur in practice; except for pathological cases, it can happen only
when the new size is extremely close to the minimum possible.
.Pp
Has no intelligence whatever when it comes to allocating blocks to copy
data into when shrinking.