When I try to mount the /dev/sdd1 device then it give error

mount -t ext3 /dev/sdd1 /4hd

mount:/dev/sdd1 is not a valid block device

Please advice.

Regards

If it is a valid block device then you should see it in a root terminal with command
Secondly sdd1 will be listed in /dev directory.

No good to argue with the kernel, get the evidence.

I cannot see /dev/sdd1 using fdisk -l. Actually I unmount this device by using umount -l /dev/sdd1 command. When I try to remount this device then it give me error.

Tell us what drives you have in your system.

Also post the outputs of

fdisk -l

and

ls -l /dev/disk/by-id/

The output of fdisk -l is

brw-rw---- 1 root disk 8, 49 Jun 7 14:08 /dev/sdd1

The output of ls -l /dev/sdd1 is

Disk /dev/hda: 120.0 GB, 120034123776 bytes
255 heads, 63 sectors/track, 14593 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hda1 1 14593 117218241 83 Linux

Disk /dev/hdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdb1 1 19457 156288321 83 Linux

Disk /dev/sda: 146.8 GB, 146815737856 bytes
255 heads, 63 sectors/track, 17849 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 64 514048+ 83 Linux
/dev/sda2 65 1108 8385930 82 Linux swap
/dev/sda3 1109 17849 134472082+ 83 Linux

Disk /dev/sdb: 36.7 GB, 36703934464 bytes
255 heads, 63 sectors/track, 4462 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 1 4462 35840983+ 83 Linux

Disk /dev/sdc: 36.7 GB, 36703934464 bytes
255 heads, 63 sectors/track, 4462 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdc1 * 1 4462 35840983+ 83 Linux

Disk /dev/sde: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sde1 1 30401 244196001 83 Linux

(BTW you 'crossed' your commands and their outputs)

Hmmm...this is indeed odd.

I know it's a bit of a Windows-y way to do things, but is this machine rebooted reasonably often? If not, you could try doing so.

Don't see any sdd disk reported so I am of same opinion as the kernel which reports

hda - 120Gb
hdb - 160Gb
sda - 146.8Gb
sdb - 36.7Gb
sdc - 36.7GB
sde - 250Gb

So may be we should ask what makes the OP thinks sdd is a block device? Could it be a CD rom?

What kind of device is /dev/sdd? Hard disk? CD/DVD? Flash disk? Camera or other USB gadget? Something else altogether? Does the device require some other kind of bus such as USB, Firewire, etc, in order to work? If so, perhaps unloading and re-loading the driver for said bus (or re-boot, as someone suggested earlier) would help.
--- rod.

/dev/sdd1 is Hard disk(SATA). Some days back this device generate problems,All the folders are disappeared from this device but ls -l command continuously shows the space occupied by /dev/sdd1 but not show the contents.So I unmount that device using umount -l /dev/sdd1 command,but when I try to remount that device then it give me the error.

Regards

Let's say this hard disk is on its way out.

First the files have corruption and are difficult if not impossible to access.

The second stage is the disk no longer readable. If the Bios cannot communicate with it then it cannot be mounted.

The final stage is the device no longer get detected in the Bios.

Can this be the case?