.TH jfs_tune 8 "October 28, 2002" " " "Set JFS file system parameters."

.SH NAME
.B jfs_tune
\- adjust tunable file system parameters on JFS

.SH SYNOPSIS
.B jfs_tune
[options]
.I device

.SH DESCRIPTION
.PP
.B jfs_tune
adjusts tunable parameters on a Linux JFS file system or external journal.
.B jfs_tune
must be run as root.

.PP
.I device
is the special file name corresponding to the actual device
.RI (e.g. " /dev/hdb1" )
on which a JFS file system or JFS external journal has been created.

.SH OPTIONS

.TP
.BI "\-J device="external-journal
Attach the JFS external journal located on
.I external-journal
to the JFS file system on
.IR device .
.IP
The external journal must already have been created using the command.
More than one file system may share the same external journal.
.IP
.B mkfs.jfs -J journal_dev
.I external-journal
.IP
Attach the external journal to the file system by using the command
.IP
.BI "jfs_tune -J device="external-journal
.I device
.IP
Instead of specifying a device name directly,
.I external-journal
can also be specified by either
.BI LABEL= label
or
.BI UUID= UUID
(Use
.BI "jfs_tune -l "device
to display a journal device's volume label and UUID.)

.TP
.B \-l
List the contents of the JFS file system or external journal superblock
that resides on
.IR device .

.TP
.BI \-L " volume-label"
Set the volume label of the JFS file system or external journal.
JFS labels can be at most 16 characters long; if
.I volume-label
is longer than 16 characters,
.B jfs_tune
will truncate it and print a warning.  The volume label can be used
by
.BR mount (8),
.BR fsck (8),
and
.BR /etc/fstab (5)
(and possibly others) by specifying
.BI LABEL= volume_label
instead of a block special device name like
.BR /dev/hda5 .

.TP
.BI \-U " UUID"
Set the universally unique identifier (UUID) of the file system or
external journal device to
.IR UUID .
The format of the UUID is a series of hex digits separated by hyphens,
like this:
"c1b9d5a2-f162-11cf-9ece-0020afc76f16".
The
.I UUID
parameter may also be one of the following:
.RS 1.2i
.TP
.I clear
clear the file system UUID
.TP
.I random
generate a new randomly-generated UUID
.TP
.I time
generate a new time-based UUID
.RE
.IP
The UUID may be used by
.BR mount (8),
.BR fsck (8),
and
.BR /etc/fstab (5)
(and possibly others) by specifying
.BI UUID= uuid
instead of a block special device name like
.BR /dev/hda1 .
.IP
See
.BR uuidgen (8)
for more information.

.TP
.BI \-V
Print version information and exit (regardless of any other chosen options).

.SH EXAMPLES
.LP
Set a randomly-generated UUID for the JFS file system on the 3rd
partition of the 2nd hard disk, and view the resultant superblock:
.IP
.B jfs_tune -l -U random /dev/hdb3
.IP

.LP
Attach an already existing external journal on a device labeled JFSLog
to a JFS file system on /dev/hda8:
.IP
.B jfs_tune -J device=LABEL=JFSLog /dev/hda8
.IP

.SH "REPORTING BUGS"
.PP
If you find a bug in
.B JFS
or
.BR jfs_tune ,
please report it via the bug tracking system ("Report Bugs" section) of the JFS project web site:
.nf
http://jfs.sourceforge.net/
.fi
.PP
Please send as much pertinent information as possible including any error messages resulting from running
.BR jfs_tune .

.SH SEE ALSO
.BR jfs_fsck (8) ,
.BR jfs_mkfs (8) ,
.BR jfs_fscklog (8) ,
.BR jfs_logdump (8) ,
.BR jfs_debugfs (8)


.SH AUTHOR
.nf
Barry Arndt  (barndt@us.ibm.com)

.fi
.B jfs_tune
is maintained by IBM.
.nf
See the JFS project web site for more details:
http://jfs.sourceforge.net/
.fi