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

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[[Category:Hardware detection and troubleshooting]]
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#REDIRECT [[udev#Writing udev rules]]
[[Category:File systems]]
 
[[es: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 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==
 
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:
 
{{hc|$ ./usb-show-serial /dev/''sdX'' ''label''|2=
 
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 {{ic|sda}} as needed):
 
{{hc|$ udevadm info -a -p $(udevadm info -q path -n /dev/sda)|2=
 
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 {{ic|<nowiki>ATTRS{serial}</nowiki>}}, so use {{ic|grep}} to filter the information:
 
{{hc|$ udevadm info -a -p $(udevadm info -q path -n /dev/sda) <nowiki>| grep ATTRS{serial}</nowiki>|2=
 
  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 {{ic|grep}}:
 
{{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}=="EHCI Host Controller"
 
}}
 
The first choice is obviously the correct one.
 
 
 
==Create udev rule==
 
Use the {{ic|<nowiki>ATTRS{serial}</nowiki>}} in a udev rule as follows. Place it in {{ic|/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 {{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
 
 
 
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 {{ic|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 {{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 {{ic|/dev/usbpen}}, which is then set in {{ic|fstab}} to mount on {{ic|/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 {{ic|/dev/usbdisk}}, and partitions 1, 2, 3 etc., to {{ic|/dev/usbdisk1}}, {{ic|/dev/usbdisk2}}, {{ic|/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 {{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
 
SUBSYSTEMS=="usb", ATTRS{serial}=="1730C13B18000B84", KERNEL=="sd*", SYMLINK+="usbdisk%n"
 
 
 
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
 
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 {{ic|/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 {{ic|/dev/mykey}} and all of other keys to {{ic|/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 {{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:
 
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.
 

Latest revision as of 07:29, 8 August 2013