'\" t
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.\" Copyright 2013 Darik Horn <dajhorn@vanadac.com>. All rights reserved.
.\"
.TH zhack 1 "2013 MAR 16" "ZFS on Linux" "User Commands"

.SH NAME
zhack \- 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
.LP
.BI "zhack [\-c " "cachefile" "] [\-d " "dir" "] <" "subcommand" "> [" "arguments" "]"
.SH OPTIONS
.HP
.BI "\-c" " cachefile"
.IP
Read the \fIpool\fR configuration from the \fIcachefile\fR, which is
/etc/zfs/zpool.cache by default.
.HP
.BI "\-d" " dir"
.IP
Search for \fIpool\fR members in the \fIdir\fR path. Can be specified
more than once.
.SH SUBCOMMANDS
.LP
.BI "feature stat " "pool"
.IP
List feature flags.
.LP
.BI "feature enable [\-d " "description" "] [\-r] " "pool guid"
.IP
Add a new feature to \fIpool\fR that is uniquely identified by
\fIguid\fR, which is specified in the same form as a zfs(8) user
property.
.IP
The \fIdescription\fR is a short human readable explanation of the new
feature.
.IP
The \fB\-r\fR switch indicates that \fIpool\fR can be safely opened
in read-only mode by a system that does not have the \fIguid\fR
feature.
.LP
.BI "feature ref [\-d|\-m] " "pool guid"
.IP
Increment the reference count of the \fIguid\fR feature in \fIpool\fR.
.IP
The \fB\-d\fR switch decrements the reference count of the \fIguid\fR
feature in \fIpool\fR.
.IP
The \fB\-m\fR switch indicates that the \fIguid\fR feature is now
required to read the pool MOS.
.SH EXAMPLES
.LP
.nf
# 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.
.LP
# zhack feature enable -d 'Predict future disk failures.' \\
    tank com.example:clairvoyance
.LP
# zhack feature ref tank com.example:clairvoyance
.SH AUTHORS
This man page was written by Darik Horn <dajhorn@vanadac.com>.
.SH SEE ALSO
.BR zfs (8),
.BR zpool-features (5),
.BR ztest (1)