Loopback Device Support in AIX
Technote
(FAQ)
Question
This technote discusses the use of the loopback device to
mount file or disk images in AIX
Answer
Introduction
In AIX 6100-04-00-0943 (6.1 TL4) support for a loopback
device was added to AIX and VIOS (PowerVM). This device can be used as a block
device to provide access to file images.
The file image can be an ISO image, a disk image, a filesystem or a logical volume. These images can be mounted into the filesystem tree via the /usr/sbin/loopmount command.
A loopback device can be created before mounting a file image using /usr/sbin/mkdev or the loopmount command can automatically create it.
According to the AIX 6.1 manuals on Infocenter, there are some restrictions to the loopback device:
* The varyonvg command on a disk image is not supported.
* A CD ISO, and DVD UDF+ISO, and other CD/DVD images are only supported in read-only format.
* An image file can be associated with only one loopback device.
* Loopback devices are not supported in workload partitions.
Mounting a File
To mount a file on the loopback device, the loopmount command is used. In the example below the loopback device is created automatically by the command.
Remember unlike crfs the mount point directory must already exist.
# mkdir /cdmount
# loopmount -i /backup/cd_image_327874 -l loop0 -o "-V cdrfs -o ro" -m /cdmount
# df
/dev/loop0 1678304 0 100% 419576 100% /cdmount
# lsdev -C | grep loop
loop0 Available Loopback Device
# cd /dev
# ls -l loop*
brw-rw---- 1 root system 34, 0 Nov 27 06:43 loop0
During its existence the loopback device is listed in the CuAt, CuDv and CuDvDr ODM object classes.
Unmounting a File
To unmount a file mounted on the loopback device, use /usr/sbin/loopumount. If the regular /usr/sbin/umount command is used the dynamically created loopback device will not be unconfigured.
# loopumount -l loop0 -m /cdmount
Notice that since the loop0 device was created dynamically in the previous mount it will be deleted when not needed any more.
# df | grep loop
<nothing returned>
# lsdev -C | grep loop
<nothing returned>
Possible Problems and Solutions
---------------
# loopmount -i /images/IBM.iso -l loop0 -o "-V cdrfs -o ro" -m /cdmount
1320-003 loopmount: Specified loopback device is not found in ODM
Customized Database
Using the -l option assumes the loopback device already exists in /dev and the ODM classes.
If the device doesn't exist you can create it with mkdev:
# mkdev -c loopback -s node -t loopback
loop0 Available
Then use loopmount with -i and -l options to mount into the filesystem tree.
---------------
# loopmount -i /images/IBM.iso -o "-V cdrfs -o ro" -m /cdmount
1320-007 loopmount: Failed to mount the imagefile
Make sure the mount point directory exists
Check the mount options. Readonly must be supplied.
The file image can be an ISO image, a disk image, a filesystem or a logical volume. These images can be mounted into the filesystem tree via the /usr/sbin/loopmount command.
A loopback device can be created before mounting a file image using /usr/sbin/mkdev or the loopmount command can automatically create it.
According to the AIX 6.1 manuals on Infocenter, there are some restrictions to the loopback device:
* The varyonvg command on a disk image is not supported.
* A CD ISO, and DVD UDF+ISO, and other CD/DVD images are only supported in read-only format.
* An image file can be associated with only one loopback device.
* Loopback devices are not supported in workload partitions.
Mounting a File
To mount a file on the loopback device, the loopmount command is used. In the example below the loopback device is created automatically by the command.
Remember unlike crfs the mount point directory must already exist.
# mkdir /cdmount
# loopmount -i /backup/cd_image_327874 -l loop0 -o "-V cdrfs -o ro" -m /cdmount
# df
/dev/loop0 1678304 0 100% 419576 100% /cdmount
# lsdev -C | grep loop
loop0 Available Loopback Device
# cd /dev
# ls -l loop*
brw-rw---- 1 root system 34, 0 Nov 27 06:43 loop0
During its existence the loopback device is listed in the CuAt, CuDv and CuDvDr ODM object classes.
Unmounting a File
To unmount a file mounted on the loopback device, use /usr/sbin/loopumount. If the regular /usr/sbin/umount command is used the dynamically created loopback device will not be unconfigured.
# loopumount -l loop0 -m /cdmount
Notice that since the loop0 device was created dynamically in the previous mount it will be deleted when not needed any more.
# df | grep loop
<nothing returned>
# lsdev -C | grep loop
<nothing returned>
Possible Problems and Solutions
---------------
# loopmount -i /images/IBM.iso -l loop0 -o "-V cdrfs -o ro" -m /cdmount
1320-003 loopmount: Specified loopback device is not found in ODM
Customized Database
Using the -l option assumes the loopback device already exists in /dev and the ODM classes.
If the device doesn't exist you can create it with mkdev:
# mkdev -c loopback -s node -t loopback
loop0 Available
Then use loopmount with -i and -l options to mount into the filesystem tree.
---------------
# loopmount -i /images/IBM.iso -o "-V cdrfs -o ro" -m /cdmount
1320-007 loopmount: Failed to mount the imagefile
Make sure the mount point directory exists
Check the mount options. Readonly must be supplied.