Difference between revisions of "Map Custom Device Entries with udev"

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[[Category:Hardware detection and troubleshooting (English)]]
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[[Category:Hardware detection and troubleshooting]]
[[Category:File systems (English)]]
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[[Category:File systems]]
[[Category:HOWTOs (English)]]
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[[es:Map Custom Device Entries with udev]]
{{i18n|Map Custom Device Entries with udev}}
+
This process allows to map a specific device to a constant device-node, located in {{ic|/dev}}, by using [[udev]] rules. This can then be used in [[fstab]], among other places, to ensure that the device can be mounted with a unchanging device-node--ideal for desktop shortcuts and other mounting operations.
 
+
This process allows to map a specific device to a constant device-node, located in {{filename|/dev}}, by using [[udev]] rules. This can then be used in [[fstab]], among other places, to ensure that the device can be mounted with a unchanging device-node--ideal for desktop shortcuts and other mounting operations.
+
  
 
This article focuses on USB devices and was copied almost verbatim from the [http://en.gentoo-wiki.com Gentoo wiki], later supplemented with additional hints.
 
This article focuses on USB devices and was copied almost verbatim from the [http://en.gentoo-wiki.com Gentoo wiki], later supplemented with additional hints.
  
 
==Get USB device udev information==
 
==Get USB device udev information==
Here is script that facilitates this operation. Simply plug in the device before running the script. Save it as {{filename|usb-show-serial}}, for example, and run it like so:
+
Here is script that facilitates this operation. Simply plug in the device before running the script. Save it as {{ic|usb-show-serial}}, for example, and run it like so:
{{command|name=./usb-show-serial /dev/''sdX'' ''label''|output=
+
{{hc|$ ./usb-show-serial /dev/''sdX'' ''label''|2=
 
add the following to /etc/udev/rules.d/90-automounter.rules
 
add the following to /etc/udev/rules.d/90-automounter.rules
 
BUS=="usb", ATTRS{serial}=="23560716050834460007" , KERNEL=="sd?1", NAME="%k", SYMLINK+="foo",  GROUP="storage"
 
BUS=="usb", ATTRS{serial}=="23560716050834460007" , KERNEL=="sd?1", NAME="%k", SYMLINK+="foo",  GROUP="storage"
 
}}
 
}}
The script is available [http://kaizo.org/misc/slackware/current/misc/usb-show-serial here].
+
 
 
+
 
==Manual method==
 
==Manual method==
Make sure one of the target devices is plugged in and then run the following (replacing {{filename|sda}} as needed):
+
Make sure one of the target devices is plugged in and then run the following (replacing {{ic|sda}} as needed):
{{command|name=udevadm info -a -p `udevadm info -q path -n /dev/sda`|output=
+
{{hc|$ udevadm info -a -p $(udevadm info -q path -n /dev/sda)|2=
 
Udevadm starts with the device specified by the devpath and then
 
Udevadm starts with the device specified by the devpath and then
 
walks up the chain of parent devices. It prints for every device
 
walks up the chain of parent devices. It prints for every device
Line 147: Line 144:
 
}}
 
}}
  
The only part of this that is needed is {{codeline|ATTRS{serial}}}, so use {{codeline|grep}} to filter the information:
+
The only part of this that is needed is {{ic|<nowiki>ATTRS{serial}</nowiki>}}, so use {{ic|grep}} to filter the information:
{{command|name=udevadm info -a -p `udevadm info -q path -n /dev/sda` | grep ATTRS{serial}|output=
+
{{hc|$ udevadm info -a -p $(udevadm info -q path -n /dev/sda) <nowiki>| grep ATTRS{serial}</nowiki>|2=
 
   ATTRS{serial}=="14AB0000000096"
 
   ATTRS{serial}=="14AB0000000096"
 
   ATTRS{serial}=="0000:00:02.2"
 
   ATTRS{serial}=="0000:00:02.2"
 
}}
 
}}
  
This narrows down the search to a much greater degree; however, one of the two serials is irrelevant. Trim down the {{codeline|grep}}:
+
This narrows down the search to a much greater degree; however, one of the two serials is irrelevant. Trim down the {{ic|grep}}:
{{command|name=udevadm info -a -p `udevadm info -q path -n /dev/sda` | grep ATTRS{product}|output=
+
{{hc|$ udevadm info -a -p $(udevadm info -q path -n /dev/sda) <nowiki>| grep ATTRS{product}</nowiki>|2=
 
   '''ATTRS{product}=="USB Mass Storage Device"'''
 
   '''ATTRS{product}=="USB Mass Storage Device"'''
 
   ATTRS{product}=="EHCI Host Controller"
 
   ATTRS{product}=="EHCI Host Controller"
Line 161: Line 158:
  
 
==Create udev rule==
 
==Create udev rule==
Use the {{codeline|ATTRS{serial}}} in a udev rule as follows. Place it in {{filename|/etc/udev/rules.d/00.rules}}:
+
Use the {{ic|<nowiki>ATTRS{serial}</nowiki>}} in a udev rule as follows. Place it in {{ic|/etc/udev/rules.d/00.rules}}:
  BUS=="usb", ATTRS{serial}=="14AB0000000096", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbdrive", GROUP="storage"
+
  SUBSYSTEMS=="usb", ATTRS{serial}=="14AB0000000096", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbdrive", GROUP="storage"
 
{{note|When creating a file with a different naming scheme that those in the directory, remember that udev processes these files in alphabetical order.}}
 
{{note|When creating a file with a different naming scheme that those in the directory, remember that udev processes these files in alphabetical order.}}
  
Line 169: Line 166:
 
  # mkdir /mnt/usbdrive
 
  # mkdir /mnt/usbdrive
  
In {{filename|/etc/[[fstab]]}}, create an entry as:
+
In {{ic|/etc/[[fstab]]}}, create an entry as:
 
  /dev/usbdrive /mnt/usbdrive vfat rw,noauto,group,flush,quiet,nodev,nosuid,noexec,noatime,dmask=000,fmask=111 0 0
 
  /dev/usbdrive /mnt/usbdrive vfat rw,noauto,group,flush,quiet,nodev,nosuid,noexec,noatime,dmask=000,fmask=111 0 0
  
Options {{codeline|nodev, nosuid, and noexec}} are unnecesary; they are stated for security reasons only. Additionally, depending on your locale preferences, add {{codeline|codepage}} and {{codeline|iocharset}} options (such as {{codeline|<nowiki>codepage=866,iocharset=utf-8</nowiki>}}) in order to be able to display non-Latin file-names correctly.
+
Options {{ic|nodev, nosuid, and noexec}} are unnecesary; they are stated for security reasons only. Additionally, depending on your locale preferences, add {{ic|codepage}} and {{ic|iocharset}} options (such as {{ic|<nowiki>codepage=866,iocharset=utf-8</nowiki>}}) in order to be able to display non-Latin file-names correctly.
  
Now, root and users who belongs to the {{codeline|storage}} [[group]] can mount the USB device by:
+
Now, root and users who belongs to the {{ic|storage}} [[group]] can mount the USB device by:
 
  mount /mnt/usbdrive
 
  mount /mnt/usbdrive
  
Line 185: Line 182:
  
 
==Examples==
 
==Examples==
Here are some mapping and mounting examples. This system's devices sometimes made nodes as {{filename|sda}} or {{filename|sda1}} so I two rules for each needed to be specified, which aid "device not found" problems. The {{filename|sda}} node is also needed for disk-level activities; e.g., {{codeline|fdisk /dev/sda}}.
+
Here are some mapping and mounting examples. This system's devices sometimes made nodes as {{ic|sda}} or {{ic|sda1}} so I two rules for each needed to be specified, which aid "device not found" problems. The {{ic|sda}} node is also needed for disk-level activities; e.g., {{ic|fdisk /dev/sda}}.
  
This always maps a specific USB device (in this case, a pendrive) to {{filename|/dev/usbpen}}, which is then set in {{filename|fstab}} to mount on {{filename|/mnt/usbpen}}:
+
This always maps a specific USB device (in this case, a pendrive) to {{ic|/dev/usbpen}}, which is then set in {{ic|fstab}} to mount on {{ic|/mnt/usbpen}}:
 
  # Symlink USB pen
 
  # Symlink USB pen
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbpen", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbpen", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbpen", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbpen", GROUP="storage"
  
If for devices with multiple partitions, the following example maps the device to {{filename|/dev/usbdisk}}, and partitions 1, 2, 3 etc., to {{filename|/dev/usbdisk1}}, {{filename|/dev/usbdisk2}}, {{filename|/dev/usbdisk3}}, etc.
+
If for devices with multiple partitions, the following example maps the device to {{ic|/dev/usbdisk}}, and partitions 1, 2, 3 etc., to {{ic|/dev/usbdisk1}}, {{ic|/dev/usbdisk2}}, {{ic|/dev/usbdisk3}}, etc.
 
  # Symlink multi-part device
 
  # Symlink multi-part device
 
  SUSSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbdisk", GROUP="storage"
 
  SUSSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbdisk", GROUP="storage"
Line 201: Line 198:
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", NAME="%k", SYMLINK+="usbdisk%n", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", NAME="%k", SYMLINK+="usbdisk%n", GROUP="storage"
  
It's also possible to omit the {{codeline|NAME}} and {{codeline|GROUP}} statements, so that the defaults from {{filename|udev.rules}} are used. Meaning that the shortest and simplest solution would be adding this rule:
+
It's also possible to omit the {{ic|NAME}} and {{ic|GROUP}} statements, so that the defaults from {{ic|udev.rules}} are used. Meaning that the shortest and simplest solution would be adding this rule:
 
  # Symlink multi-part device
 
  # Symlink multi-part device
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", SYMLINK+="usbdisk%n"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", SYMLINK+="usbdisk%n"
  
This always maps a Olympus digicam to {{filename|/dev/usbcam}}, which can be stated in {{filename|fstab}} to mount on {{filename|/mnt/usbcam}}:
+
This always maps a Olympus digicam to {{ic|/dev/usbcam}}, which can be stated in {{ic|fstab}} to mount on {{ic|/mnt/usbcam}}:
 
  # Symlink USB camera
 
  # Symlink USB camera
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?", NAME="%k", SYMLINK+="usbcam", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?", NAME="%k", SYMLINK+="usbcam", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbcam", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbcam", GROUP="storage"
  
And this maps a Packard Bell MP3 player to {{filename|/dev/mp3player}}:
+
And this maps a Packard Bell MP3 player to {{ic|/dev/mp3player}}:
 
  # Symlink MP3 player
 
  # Symlink MP3 player
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?", NAME="%k", SYMLINK+="mp3player", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?", NAME="%k", SYMLINK+="mp3player", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?1", NAME="%k", SYMLINK+="mp3player", GROUP="storage"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?1", NAME="%k", SYMLINK+="mp3player", GROUP="storage"
  
To map a selected usb-key to {{filename|/dev/mykey}} and all of other keys to {{filename|/dev/otherkey}}:
+
To map a selected usb-key to {{ic|/dev/mykey}} and all of other keys to {{ic|/dev/otherkey}}:
 
  # Symlink USB keys
 
  # Symlink USB keys
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="insert serial key", KERNEL=="sd?1", NAME="%k", SYMLINK+="mykey"
 
  SUBSYSTEMS=="usb", ATTRS{serial}=="insert serial key", KERNEL=="sd?1", NAME="%k", SYMLINK+="mykey"
 
  SUBSYSTEMS=="usb", KERNEL=="sd?1", NAME="%k", SYMLINK+="otherkey"
 
  SUBSYSTEMS=="usb", KERNEL=="sd?1", NAME="%k", SYMLINK+="otherkey"
Note the order of the lines. Since all the USB keys should create the {{filename|/dev/sd<a||b>}} node, udev will first check if it is a rules-stated USB-key, defined by serial number. But if an unknown USB-key is plugged, it will create ''also'' create a node, using the previously stated generic name, "otherkey". That rule should be the last one in rules file so that it does not override the others.
+
Note the order of the lines. Since all the USB keys should create the {{ic|<nowiki>/dev/sd<a||b></nowiki>}} node, udev will first check if it is a rules-stated USB-key, defined by serial number. But if an unknown USB-key is plugged, it will create ''also'' create a node, using the previously stated generic name, "otherkey". That rule should be the last one in rules file so that it does not override the others.
  
 
This is an example on how to distinguish USB HDD drives and USB sticks:
 
This is an example on how to distinguish USB HDD drives and USB sticks:

Revision as of 14:17, 26 September 2012

This process allows to map a specific device to a constant device-node, located in /dev, by using udev rules. This can then be used in fstab, among other places, to ensure that the device can be mounted with a unchanging device-node--ideal for desktop shortcuts and other mounting operations.

This article focuses on USB devices and was copied almost verbatim from the Gentoo wiki, later supplemented with additional hints.

Get USB device udev information

Here is script that facilitates this operation. Simply plug in the device before running the script. Save it as usb-show-serial, for example, and run it like so:

$ ./usb-show-serial /dev/sdX label
add the following to /etc/udev/rules.d/90-automounter.rules
BUS=="usb", ATTRS{serial}=="23560716050834460007" , KERNEL=="sd?1", NAME="%k", SYMLINK+="foo",  GROUP="storage"

Manual method

Make sure one of the target devices is plugged in and then run the following (replacing sda as needed):

$ udevadm info -a -p $(udevadm info -q path -n /dev/sda)
Udevadm starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/block/sda':
    KERNEL=="sda"
    SUBSYSTEM=="block"
    DRIVER==""
    ATTR{stat}=="      19      111      137      160        0        0        0        0        0      152      160"
    ATTR{size}=="2007040"
    ATTR{removable}=="1"
    ATTR{range}=="16"
    ATTR{dev}=="8:0"

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1/1-5/1-5:1.0/host5/target5:0:0/5:0:0:0':
    KERNELS=="5:0:0:0"
    SUBSYSTEMS=="scsi"
    DRIVERS=="sd"
    ATTRS{ioerr_cnt}=="0x0"
    ATTRS{iodone_cnt}=="0x1c"
    ATTRS{iorequest_cnt}=="0x1c"
    ATTRS{iocounterbits}=="32"
    ATTRS{timeout}=="30"
    ATTRS{state}=="running"
    ATTRS{rev}=="1.20"
    ATTRS{model}=="01GB Tiny       "
    ATTRS{vendor}=="Pretec  "
    ATTRS{scsi_level}=="3"
    ATTRS{type}=="0"
    ATTRS{queue_type}=="none"
    ATTRS{queue_depth}=="1"
    ATTRS{device_blocked}=="0"
    ATTRS{max_sectors}=="240"

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1/1-5/1-5:1.0/host5/target5:0:0':
    KERNELS=="target5:0:0"
    SUBSYSTEMS==""
    DRIVERS==""

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1/1-5/1-5:1.0/host5':
    KERNELS=="host5"
    SUBSYSTEMS==""
    DRIVERS==""

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1/1-5/1-5:1.0':
    KERNELS=="1-5:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb-storage"
    ATTRS{modalias}=="usb:v4146pBA01d0100dc00dsc00dp00ic08isc06ip50"
    ATTRS{bInterfaceProtocol}=="50"
    ATTRS{bInterfaceSubClass}=="06"
    ATTRS{bInterfaceClass}=="08"
    ATTRS{bNumEndpoints}=="03"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceNumber}=="00"

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1/1-5':
    KERNELS=="1-5"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{serial}=="14AB0000000096"
    ATTRS{product}=="USB Mass Storage Device"
    ATTRS{maxchild}=="0"
    ATTRS{version}==" 2.00"
    ATTRS{devnum}=="7"
    ATTRS{speed}=="480"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bcdDevice}=="0100"
    ATTRS{idProduct}=="ba01"
    ATTRS{idVendor}=="4146"
    ATTRS{bMaxPower}==" 98mA"
    ATTRS{bmAttributes}=="80"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bNumInterfaces}==" 1"

  looking at parent device '/devices/pci0000:00/0000:00:02.2/usb1':
    KERNELS=="usb1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{serial}=="0000:00:02.2"
    ATTRS{product}=="EHCI Host Controller"
    ATTRS{manufacturer}=="Linux 2.6.18-ARCH ehci_hcd"
    ATTRS{maxchild}=="6"
    ATTRS{version}==" 2.00"
    ATTRS{devnum}=="1"
    ATTRS{speed}=="480"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bcdDevice}=="0206"
    ATTRS{idProduct}=="0000"
    ATTRS{idVendor}=="0000"
    ATTRS{bMaxPower}=="  0mA"
    ATTRS{bmAttributes}=="e0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bNumInterfaces}==" 1"

  looking at parent device '/devices/pci0000:00/0000:00:02.2':
    KERNELS=="0000:00:02.2"
    SUBSYSTEMS=="pci"
    DRIVERS=="ehci_hcd"
    ATTRS{broken_parity_status}=="0"
    ATTRS{enable}=="1"
    ATTRS{modalias}=="pci:v000010DEd00000068sv00001043sd00000C11bc0Csc03i20"
    ATTRS{local_cpus}=="f"
    ATTRS{irq}=="17"
    ATTRS{class}=="0x0c0320"
    ATTRS{subsystem_device}=="0x0c11"
    ATTRS{subsystem_vendor}=="0x1043"
    ATTRS{device}=="0x0068"
    ATTRS{vendor}=="0x10de"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

The only part of this that is needed is ATTRS{serial}, so use grep to filter the information:

$ udevadm info -a -p $(udevadm info -q path -n /dev/sda) | grep ATTRS{serial}
ATTRS{serial}=="14AB0000000096"
   ATTRS{serial}=="0000:00:02.2"

This narrows down the search to a much greater degree; however, one of the two serials is irrelevant. Trim down the grep:

$ udevadm info -a -p $(udevadm info -q path -n /dev/sda) | grep ATTRS{product}
ATTRS{product}=="USB Mass Storage Device"
   ATTRS{product}=="EHCI Host Controller"

The first choice is obviously the correct one.

Create udev rule

Use the ATTRS{serial} in a udev rule as follows. Place it in /etc/udev/rules.d/00.rules:

SUBSYSTEMS=="usb", ATTRS{serial}=="14AB0000000096", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbdrive", GROUP="storage"
Note: When creating a file with a different naming scheme that those in the directory, remember that udev processes these files in alphabetical order.

Make fstab entry

Create a directory for mounting:

# mkdir /mnt/usbdrive

In /etc/fstab, create an entry as:

/dev/usbdrive /mnt/usbdrive vfat rw,noauto,group,flush,quiet,nodev,nosuid,noexec,noatime,dmask=000,fmask=111 0 0

Options nodev, nosuid, and noexec are unnecesary; they are stated for security reasons only. Additionally, depending on your locale preferences, add codepage and iocharset options (such as codepage=866,iocharset=utf-8) in order to be able to display non-Latin file-names correctly.

Now, root and users who belongs to the storage group can mount the USB device by:

mount /mnt/usbdrive

To allow a non-root user to access to USB devices, add them to the storage group:

# gpasswd -a username storage

Restart udev

To load the updated rules, run:

# udevadm control --reload-rules

Examples

Here are some mapping and mounting examples. This system's devices sometimes made nodes as sda or sda1 so I two rules for each needed to be specified, which aid "device not found" problems. The sda node is also needed for disk-level activities; e.g., fdisk /dev/sda.

This always maps a specific USB device (in this case, a pendrive) to /dev/usbpen, which is then set in fstab to mount on /mnt/usbpen:

# Symlink USB pen
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbpen", GROUP="storage"
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbpen", GROUP="storage"

If for devices with multiple partitions, the following example maps the device to /dev/usbdisk, and partitions 1, 2, 3 etc., to /dev/usbdisk1, /dev/usbdisk2, /dev/usbdisk3, etc.

# Symlink multi-part device
SUSSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?", NAME="%k", SYMLINK+="usbdisk", GROUP="storage"
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd?[1-9]", NAME="%k", SYMLINK+="usbdisk%n", GROUP="storage"

The above rules are equivalent to the following one:

# Symlink multi-part device
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", NAME="%k", SYMLINK+="usbdisk%n", GROUP="storage"

It's also possible to omit the NAME and GROUP statements, so that the defaults from udev.rules are used. Meaning that the shortest and simplest solution would be adding this rule:

# Symlink multi-part device
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", SYMLINK+="usbdisk%n"

This always maps a Olympus digicam to /dev/usbcam, which can be stated in fstab to mount on /mnt/usbcam:

# Symlink USB camera
SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?", NAME="%k", SYMLINK+="usbcam", GROUP="storage"
SUBSYSTEMS=="usb", ATTRS{serial}=="000207532049", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbcam", GROUP="storage"

And this maps a Packard Bell MP3 player to /dev/mp3player:

# Symlink MP3 player
SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?", NAME="%k", SYMLINK+="mp3player", GROUP="storage"
SUBSYSTEMS=="usb", ATTRS{serial}=="0002F5CF72C9C691", KERNEL=="sd?1", NAME="%k", SYMLINK+="mp3player", GROUP="storage"

To map a selected usb-key to /dev/mykey and all of other keys to /dev/otherkey:

# Symlink USB keys
SUBSYSTEMS=="usb", ATTRS{serial}=="insert serial key", KERNEL=="sd?1", NAME="%k", SYMLINK+="mykey"
SUBSYSTEMS=="usb", KERNEL=="sd?1", NAME="%k", SYMLINK+="otherkey"

Note the order of the lines. Since all the USB keys should create the /dev/sd<a||b> node, udev will first check if it is a rules-stated USB-key, defined by serial number. But if an unknown USB-key is plugged, it will create also create a node, using the previously stated generic name, "otherkey". That rule should be the last one in rules file so that it does not override the others.

This is an example on how to distinguish USB HDD drives and USB sticks:

BUS=="usb", ATTRS{product}=="USB2.0 Storage Device", KERNEL=="sd?", NAME="%k", SYMLINK+="usbdisk", GROUP="storage"
BUS=="usb", ATTRS{product}=="USB2.0 Storage Device", KERNEL=="sd?[1-9]", NAME="%k", SYMLINK+="usbdisk%n", GROUP="storage"
BUS=="usb", ATTRS{product}=="USB Mass Storage Device", KERNEL=="sd?1", NAME="%k", SYMLINK+="usbflash", GROUP="storage"

Note that this udev rule doesn't use serials at all.