Trying to mount an SD card connected via a USB SD-card reader.

dmesg shows that the USB device is connected and the card is detected

[   84.696147] usb 1-3.2: new high-speed USB device number 7 using ehci-pci
[   84.791437] usb 1-3.2: New USB device found, idVendor=8564, idProduct=4000
[   84.791443] usb 1-3.2: New USB device strings: Mfr=3, Product=4, SerialNumber=5
[   84.791446] usb 1-3.2: Product: Transcend
[   84.791450] usb 1-3.2: Manufacturer: TS-RDF5 
[   84.791452] usb 1-3.2: SerialNumber: 000000000039
[   85.060511] usb-storage 1-3.2:1.0: USB Mass Storage device detected
[   85.060953] scsi6 : usb-storage 1-3.2:1.0
[   85.061055] usbcore: registered new interface driver usb-storage
[   85.089647] usbcore: registered new interface driver uas
[   86.061604] scsi 6:0:0:0: Direct-Access     TS-RDF5  SD  Transcend    TS37 PQ: 0 ANSI: 6
[   86.061964] sd 6:0:0:0: Attached scsi generic sg2 type 0
[   86.575707] sd 6:0:0:0: [sdb] 61896704 512-byte logical blocks: (31.6 GB/29.5 GiB)
[   86.576965] sd 6:0:0:0: [sdb] Write Protect is off
[   86.576970] sd 6:0:0:0: [sdb] Mode Sense: 23 00 00 00
[   86.578223] sd 6:0:0:0: [sdb] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[   86.585246]  sdb: [CUMANA/ADFS] sdb1 [ADFS] sdb1
[   86.590856] sd 6:0:0:0: [sdb] Attached SCSI removable disk

fdisk shows that it is connected, although it complains about some invalid argument:

$ sudo fdisk -l

Disk /dev/sdb: 31.7 GB, 31691112448 bytes
64 heads, 32 sectors/track, 30223 cylinders, total 61896704 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00006f83

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     2474609     1236281    e  W95 FAT16 (LBA)
/dev/sdb2         2482176    61896703    29707264   85  Linux extended
/dev/sdb5         2490368     2605055       57344    c  W95 FAT32 (LBA)
/dev/sdb6         2607104    11855871     4624384   83  Linux
/dev/sdb7        11857920    61396991    24769536   83  Linux
fdisk: unable to seek on /dev/sdb1: Invalid argument

When trying to mount, I get the "special device does not exist" message:

$ sudo mount /dev/sdb2 /mnt -v
mount: you didn't specify a filesystem type for /dev/sdb2
       I will try all types mentioned in /etc/filesystems or /proc/filesystems
Trying ext3
mount: special device /dev/sdb2 does not exist

Any idea?

  • The kernel logs are inconsistent with the fdisk output: they only list sdb as a partition. Are there any more logs about this device, maybe some read errors? Can you try it in another reader? Commented Oct 29, 2016 at 21:18

2 Answers 2


The extended partition sdb2 contains partitions 5 and up. So try mounting the other partitions instead (sdb1 and sdb5 if labelled correctly are FAT / msdos, sdb6 and sdb7 are linux, possibly ext3/4).

  • I have also tried for sdb6 and sdb7, but they got the same. Commented Oct 28, 2016 at 22:08
  • Are you positive there are valid filesystems on there? It seems an atypical partition layout for a USB stick - maybe it has just been someones fdisk experiment? The symptoms might fit with partitions that were created but without creating a filesystem on there. Commented Oct 28, 2016 at 22:15
  • The filesystem certainly was there, as this SD card was used in a raspberry pi earlier, but it is possible that it got damaged. That is exactly what I am trying to figure out. Basically what I would need to know whether there is any other explanation to this mounting error other than the SD card being damaged. Commented Oct 28, 2016 at 22:50

Note this line in dmesg output:

[   86.585246]  sdb: [CUMANA/ADFS] sdb1 [ADFS] sdb1

This indicates the kernel has support for Acorn CUMANA partition tables built in, in addition to the more familiar MBR and GPT partition types of the x86 world.

Because of the the simplicity of the CUMANA partition structure, it can cause a misdetection of MBR partitioned disk as CUMANA/ADFS partition type. That is exactly what seems to be happening here.

See also:

Ubuntu bug #1453117 (fixed in Ubuntu kernel version 3.19.0-26.28)

Linux kernel bug #4054

Andries Brouwer 2005-01-17 14:49:22 UTC

This is a consequence of enabling CONFIG_ACORN_PARTITION_CUMANA: a 1 in 256 probability of getting any random partition recognized as CUMANA/ADFS. Solution: do not enable CONFIG_ACORN_PARTITION_CUMANA.

The CUMANA partition support is only needed if you deal with disks or disk images from old Acorn computers with a Cumana disk controller. In other words, disabling this feature is definitely the right solution for everyone who is not specifically dealing with old Acorn hardware or an Acorn emulator.

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