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System Administration Commandslofiadm(1M)


 lofiadm - administer files available as block devices through lofi


 /usr/sbin/lofiadm -a file [device]
 /usr/sbin/lofiadm -d file | device
 /usr/sbin/lofiadm [ file | device]



lofiadm administers lofi(7D), the loopback file driver. lofi(7d) allows a file to be associated with a block device. That file can then be accessed through the block device. This is useful when the file contains an image of some filesystem (such as a floppy or CD-ROM image), because the block device can then be used with the normal system utilities for mounting, checking or repairing filesystems. See fsck(1M) and mount(1M).

Use lofiadm to add a file as a loopback device, remove such an association, or print information about the current associations.



The following options are supported:

-a file [device]
Add file as a block device.

If device is not specified, an available device is picked.

If device is specified, lofiadm attempts to assign it to file. device must be available or lofiadm will fail. The ability to specify a device is provided for use in scripts that wish to re-establish a particular set of associations.

-d file | device
Remove an association by file or device name, if the associated block device is not busy, and deallocates the block device.



The following operands are supported:

Print the block device associated with file.
Print the file name associated with the block device device.

Without arguments, print a list of the current associations. Filenames must be valid absolute pathnames.

When a file is added, it is opened for reading or writing by root. Any restrictions apply (such as restricted root access over NFS). The file is held open until the association is removed. It is not actually accessed until the block device is used, so it will never be written to if the block device is only opened read-only.


 Example 1. Mounting an Existing CD-ROM Image

You should ensure that Solaris understands the image before creating the CD. lofi allows you to mount the image and see if it works.

This example mounts an existing CD-ROM image (sparc.iso), of the Red Hat 6.0 CD which was downloaded from the Internet. It was created with the mkisofs utility from the Internet.

Use lofiadm to attach a block device to it:

# lofiadm -a /home/mike_s/RH6.0/sparc.iso

lofiadm picks the device and prints the device name to the standard output. You can run lofiadm again by issuing the following command:

# lofiadm
Block Device     File 
/dev/lofi/1      /home/mike_s/RH6.0/sparc.iso

Or, you can give it one name and ask for the other, by issuing the following command:

# lofiadm /dev/lofi/1

Use the mount command to mount the image:
# mount -F hsfs -o ro /dev/lofi/1 /mnt

Check to ensure that Solaris understands the image:

# df -k /mnt
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/lofi/1           512418  512418       0   100%    /mnt 
# ls /mnt 
./            RedHat/       doc/          ls-lR         rr_moved/ 
../           TRANS.TBL     dosutils/     ls-lR.gz      sbin@ 
.buildlog     bin@          etc@          misc/         tmp/ 
COPYING       boot/         images/       mnt/          usr@ 
README*     kernels/      modules/ 
RPM-PGP-KEY   dev@          lib@          proc/

Solaris can mount the CD-ROM image, and understand the filenames. The image was created properly, and you can now create the CD-ROM with confidence.

As a final step, unmount and detach the images:

# umount /mnt 
# lofiadm -d /dev/lofi/1 
# lofiadm 
Block Device             File

Example 2. Mounting a Floppy Image

This is similar to Example 1.

Using lofi to help you mount files that contain floppy images is helpful if a floppy disk contains a file that you need, but the machine which you're on doesn't have a floppy drive. It is also helpful if you don't want to take the time to use the dd command to copy the image to a floppy.

This is an example of getting to MDB floppy for Solaris x86:

# lofiadm -a /export/s28/MDB_s28x_wos/latest/boot.3
# mount -F pcfs /dev/lofi/1 /mnt
# ls /mnt
./            COMMENT.BAT*  RC.D/         SOLARIS.MAP*
../           IDENT*        REPLACE.BAT*  X/
# umount /mnt
# lofiadm -d /export/s28/MDB_s28x_wos/latest/boot.3
Example 3. Making a UFS Filesystem on a File

Making a UFS filesystm on a file can be useful, particularly if a test suite requires a scratch filesystem. It can be painful (or annoying) to have to re-partition a disk just for the test suite, but you don't have to. You can newfs a file with lofi

Create the file:

# mkfile 35m /export/home/test

Attach it to a block device. You also get the character device that newfs requires, so newfs that:

# lofiadm -a /export/home/test
# newfs /dev/rlofi/1
newfs: construct a new file system /dev/rlofi/1: (y/n)? y
/dev/rlofi/1:   71638 sectors in 119 cylinders of 1 tracks, 602 sectors
        35.0MB in 8 cyl groups (16 c/g, 4.70MB/g, 2240 i/g)
super-block backups (for fsck -F ufs -o b=#) at:
 32, 9664, 19296, 28928, 38560, 48192, 57824, 67456,

Note that ufs might not be able to use the entire file. Mount and use the filesystem:

# mount /dev/lofi/1 /mnt
# df -k /mnt
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/lofi/1            33455       9   30101     1%    /mnt
# ls /mnt
./           ../          lost+found/
# umount /mnt
# lofiadm -d /dev/lofi/1
Example 4. Creating a PC (FAT) File System on a Unix File

The following series of commands creates a FAT file system on a Unix file. The file is associated with a block device created by lofiadm.

# mkfile 10M /export/test/testfs
# lofiadm -a /export/test testfs
Note use of rlofi, not lofi, in following command.
# mkfs -F pcfs -o nofdisk,size=20480 /dev/rlofi/1
Construct a new FAT file system on /dev/rlofi/1: (y/n)? y
# mount -F pcfs /dev/lofi/1 /mnt
# cd /mnt
# df -k .
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/lofi/1            10142       0   10142     0%    /mnt



See environ(5) for descriptions of the following environment variables that affect the execution of lofiadm: LC_CTYPE, LC_MESSAGES and NLSPATH.



The following exit values are returned:

Successful completion.
An error occurred.



See attributes(5) for descriptions of the following attributes:




fsck(1M), mount(1M), mount_ufs(1M), attributes(5), lofi(7D), lofs(7FS)



Just as you would not directly access a disk device that has mounted file systems, you should not access a file associated with a block device except through the lofi file driver. It might also be appropriate to ensure that the file has appropriate permissions to prevent such access.

Associations are not persistant across reboots. A script can be used to re-establish them if required.

The abilities of lofiadm, and who can use them, are controlled by the permissions of /dev/lofictl. Read-access allows query operations, such as listing all the associations. Write-access is required to do any state-changing operations, like adding an association. As shipped, /dev/lofictl is owned by root, in group sys, and mode 0644, so all users can do query operations but only root can change anything. The administrator can give users write-access, allowing them to add or delete associations, but that is very likely a security hole and should probably only be given to a trusted group.

When mounting a filesystem image, take care to use appropriate mount options. In particular, the nosuid mount option might be appropriate for UFS images whose origin is unknown. Also, some options might not be useful or appropriate, like logging or forcedirectio for UFS. For compatibility purposes, a raw device is also exported along with the block device. For example, newfs(1M) requires one.

The output of lofiadm (without arguments) might change in future releases.

SunOS 5.9Go To TopLast Changed 17 Nov 1999

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.