.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_tuneadjusts tunable parameters on a Linux JFS file system or external journal..B jfs_tunemust be run as root..PP.I deviceis 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.B Only supported on JFS versions (1.0.18 or later) that support external journal.Attach the JFS external journal located on.I external-journalto the JFS file system on.IR device ..IPCurrently, you may only attach a single JFS file system device to a singleJFS external journal (i.e. each JFS file system using an external journalmust have a unique external journal)..IPThe external journal must already have been created using the command.IP.B mkfs.jfs -J journal_dev.I external-journal.IPAttach the external journal to the file system by using the command.IP.BI "jfs_tune -J device="external-journal.I device.IPInstead of specifying a device name directly,.I external-journalcan also be specified by either.BI LABEL= labelor.BI UUID= UUID(Use.BI "jfs_tune -l "deviceto display a journal device's volume label and UUID.).TP.B \-lList the contents of the JFS file system or external journal superblockthat 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-labelis longer than 16 characters,.B jfs_tunewill truncate it and print a warning.  The volume label can be usedby.BR mount (8),.BR fsck (8),and.BR /etc/fstab (5)(and possibly others) by specifying.BI LABEL= volume_labelinstead of a block special device name like.BR /dev/hda5 ..TP.BI \-U " UUID"Set the universally unique identifier (UUID) of the file system orexternal 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 UUIDparameter may also be one of the following:.RS 1.2i.TP.I clearclear the file system UUID.TP.I randomgenerate a new randomly-generated UUID.TP.I timegenerate a new time-based UUID.RE.IPThe UUID may be used by.BR mount (8),.BR fsck (8),and.BR /etc/fstab (5)(and possibly others) by specifying.BI UUID= uuidinstead of a block special device name like.BR /dev/hda1 ..IPSee.BR uuidgen (8)for more information..TP.BI \-VPrint version information and exit (regardless of any other chosen options)..SH EXAMPLES.LPSet a randomly-generated UUID for the JFS file system on the 3rdpartition of the 2nd hard disk, and view the resultant superblock:.IP.B jfs_tune -l -U random /dev/hdb3.IP.LPAttach an already existing external journal on a device labeled JFSLogto a JFS file system on /dev/hda8:.IP.B jfs_tune -J device=LABEL=JFSLog /dev/hda8.IP.SH "REPORTING BUGS".PPIf you find a bug in.B JFSor.BR jfs_tune ,please report it via the bug tracking system ("Report Bugs" section) of the JFS project web site:.nfhttp://jfs.sourceforge.net/.fi.PPPlease 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.nfBarry Arndt  (barndt@us.ibm.com).fi.B jfs_tuneis maintained by IBM..nfSee the JFS project web site for more details:http://jfs.sourceforge.net/.fi