When you plug in a USB card reader, a number of devices will be added (depending on the number of cards supported by the reader). Looking at dmesg output after plugging in the reader...
usb 1-2.1: new high speed USB device using ehci_hcd and address 13 usb 1-2.1: configuration #1 chosen from 1 choice scsi9 : SCSI emulation for USB Mass Storage devices usb-storage: device found at 13 usb-storage: waiting for device to settle before scanning Vendor: Generic Model: USB SD Reader Rev: 1.00 Type: Direct-Access ANSI SCSI revision: 00 sd 9:0:0:0: Attached scsi removable disk sdb Vendor: Generic Model: USB CF Reader Rev: 1.01 Type: Direct-Access ANSI SCSI revision: 00 sd 9:0:0:1: Attached scsi removable disk sdc Vendor: Generic Model: USB SM Reader Rev: 1.02 Type: Direct-Access ANSI SCSI revision: 00 sd 9:0:0:2: Attached scsi removable disk sdd Vendor: Generic Model: USB MS Reader Rev: 1.03 Type: Direct-Access ANSI SCSI revision: 00 sd 9:0:0:3: Attached scsi removable disk sde usb-storage: device scan complete
In this case, devices /dev/sdb, sdc, sdd and sde have been added. However, if there were no cards in the reader when you plugged it in, there will be no devices present that allow you to mount, hence access, the card.
steph@slap ~ $ mount /mnt/sdb1
mount: can't find /mnt/sdb1 in /etc/fstab or /etc/mtab
If there was a card in the reader when you plugged it in, e.g. in the first slot, then it would be available via /dev/sdb1.
So, how do you rescan the device so that you don't have to plug in the card reader every time you want to add/remove a card?...
Use hdparm to rescan the appropriate device:
hdparm -z [device]
hdparm is normally only usable by superusers (it's normally located at /sbin/hdparm), so you'll either have to log in as a superuser or run the command via sudo. e.g:
steph@slap ~ $ sudo hdparm -z /dev/sdb
/dev/sdb:
re-reading partition table
dmesg will show something like the following:
SCSI device sdb: 7959552 512-byte hdwr sectors (4075 MB) sdb: Write Protect is off sdb: Mode Sense: 03 00 00 00 sdb: assuming drive cache: write through sdb: sdb1
You should now be able to mount the card.
