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.\" Copyright 2013 Darik Horn <dajhorn@vanadac.com>. All rights reserved.
.\"
.\" lint-ok: WARNING: sections out of conventional order: Sh SYNOPSIS
.\"
.Dd May 26, 2021
.Dt ZHACK 1
.Os
.
.Sh NAME
.Nm zhack
.Nd libzpool debugging tool
.Sh DESCRIPTION
This utility pokes configuration changes directly into a ZFS pool,
which is dangerous and can cause data corruption.
.Sh SYNOPSIS
.Bl -tag -width Ds
.It Xo
.Nm zhack
.Cm feature stat
.Ar pool
.Xc
List feature flags.
.
.It Xo
.Nm zhack
.Cm feature enable
.Op Fl d Ar description
.Op Fl r
.Ar pool
.Ar guid
.Xc
Add a new feature to
.Ar pool
that is uniquely identified by
.Ar guid ,
which is specified in the same form as a
.Xr zfs 8
user property.
.Pp
The
.Ar description
is a short human readable explanation of the new feature.
.Pp
The
.Fl r
flag indicates that
.Ar pool
can be safely opened in read-only mode by a system that does not understand the
.Ar guid
feature.
.
.It Xo
.Nm zhack
.Cm feature ref
.Op Fl d Ns | Ns Fl m
.Ar pool
.Ar guid
.Xc
Increment the reference count of the
.Ar guid
feature in
.Ar pool .
.Pp
The
.Fl d
flag decrements the reference count of the
.Ar guid
feature in
.Ar pool
instead.
.Pp
The
.Fl m
flag indicates that the
.Ar guid
feature is now required to read the pool MOS.
.El
.
.Sh GLOBAL OPTIONS
The following can be passed to all
.Nm
invocations before any subcommand:
.Bl -tag -width "-d dir"
.It Fl c Ar cachefile
Read
.Ar pool
configuration from the
.Ar cachefile ,
which is
.Pa /etc/zfs/zpool.cache
by default.
.It Fl d Ar dir
Search for
.Ar pool
members in
.Ar dir .
Can be specified more than once.
.El
.
.Sh EXAMPLES
.Bd -literal
# zhack feature stat tank
for_read_obj:
	org.illumos:lz4_compress = 0
for_write_obj:
	com.delphix:async_destroy = 0
	com.delphix:empty_bpobj = 0
descriptions_obj:
	com.delphix:async_destroy = Destroy filesystems asynchronously.
	com.delphix:empty_bpobj = Snapshots use less space.
	org.illumos:lz4_compress = LZ4 compression algorithm support.

# zhack feature enable -d 'Predict future disk failures.' \\
    tank com.example:clairvoyance

# zhack feature ref tank com.example:clairvoyance
.Ed
.
.Sh SEE ALSO
.Xr ztest 1 ,
.Xr zpool-features 7 ,
.Xr zfs 8