Your company here — click to reach over 10,000 unique daily visitors

jfs_tune - Man Page

adjust tunable file system parameters on JFS


jfs_tune [options] device


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

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


-J device=external-journal

Attach the JFS external journal located on external-journal to the JFS file system on device.

The external journal must already have been created using the command. More than one file system may share the same external journal.

mkfs.jfs -J journal_dev external-journal

Attach the external journal to the file system by using the command

jfs_tune -J device=external-journal device

Instead of specifying a device name directly, external-journal can also be specified by either LABEL=label or UUID=UUID (Use jfs_tune -l device to display a journal device's volume label and UUID.)


List the contents of the JFS file system or external journal superblock that resides on device.

-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 volume-label is longer than 16 characters, jfs_tune will truncate it and print a warning.  The volume label can be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifying LABEL=volume_label instead of a block special device name like /dev/hda5.


Set the universally unique identifier (UUID) of the file system or external journal device to UUID. The format of the UUID is a series of hex digits separated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may also be one of the following:


clear the file system UUID


generate a new randomly-generated UUID


generate a new time-based UUID

The UUID may be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifying UUID=uuid instead of a block special device name like /dev/hda1.

See uuidgen(8) for more information.


Print version information and exit (regardless of any other chosen options).


Set a randomly-generated UUID for the JFS file system on the 3rd partition of the 2nd hard disk, and view the resultant superblock:

jfs_tune -l -U random /dev/hdb3

Attach an already existing external journal on a device labeled JFSLog to a JFS file system on /dev/hda8:

jfs_tune -J device=LABEL=JFSLog /dev/hda8

Reporting Bugs

If you find a bug in JFS or jfs_tune, please report it via the bug tracking system ("Report Bugs" section) of the JFS project web site:


Please send as much pertinent information as possible including any error messages resulting from running jfs_tune.

See Also

jfs_fsck(8), jfs_mkfs(8), jfs_fscklog(8), jfs_logdump(8), jfs_debugfs(8)


Barry Arndt  (barndt@us.ibm.com)

jfs_tune is maintained by IBM.

See the JFS project web site for more details:

Referenced By

jfs_debugfs(8), jfs_fsck(8), jfs_fscklog(8), jfs_logdump(8), jfs_mkfs(8).

October 28, 2002 Set JFS file system parameters.