У меня на машине две usb-вебкамеры, но при загрузке они иногда переключают /dev/video номер. Похоже, решением этой проблемы является создание нового правила udev. Я добавил это правило в
/etc/udev/rules.d/jj-video.rules:

Исправить веб-камеру 1

KERNEL=="video1", SUBSYSTEM=="video4linux", SUBSYSTEMS=="usb", ATTRS{idVendor}=="1d6b", ATTRS{idProduct}=="0001", SYMLINK+="webcam1"

Исправить веб-камеру 2

KERNEL=="video2", SUBSYSTEM=="video4linux", ATTR{name}=="Logitech QuickCam Pro 3000", KERNELS=="0000:00:1d.0", SUBSYSTEMS=="pci", DRIVERS=="uhci_hcd", ATTRS{vendor}=="0x8086", ATTRS##{device}=="0x2658", SYMLINK+="webcam2"

но webcam символические ссылки не создаются. Я пробовал много разных комбинаций в этом файле. Настоящие - только мои последние попытки.

Я нашел параметры в:

jjk@eee-old:~$ udevadm info -a -p $(udevadm info -q path -p /class/video4linux/video1)  

Информация Udevadm начинается с устройства, указанного в devpath, а затем идет вверх по цепочке родительских устройств. Он печатает для каждого найденного устройства все возможные атрибуты в формате ключей правил udev. Соответствующее правило может быть составлено из атрибутов устройства и атрибутов одного родительского устройства.

 looking at device '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0/video4linux/video1':
    KERNEL=="video1"
    SUBSYSTEM=="video4linux"
    DRIVER==""
    ATTR{name}=="Logitech QuickCam Pro 3000"
    ATTR{index}=="0"
    ATTR{button}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0':
    KERNELS=="2-2:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="Philips webcam"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bAlternateSetting}==" 9"
    ATTRS{bNumEndpoints}=="02"
    ATTRS{bInterfaceClass}=="0a"
    ATTRS{bInterfaceSubClass}=="ff"
    ATTRS{bInterfaceProtocol}=="00"
    ATTRS{supports_autosuspend}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:1d.0/usb2/2-2':
    KERNELS=="2-2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{bNumInterfaces}==" 3"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bmAttributes}=="a0"
    ATTRS{bMaxPower}=="500mA"
    ATTRS{urbnum}=="371076"
    ATTRS{idVendor}=="046d"
    ATTRS{idProduct}=="08b0"
    ATTRS{bcdDevice}=="0002"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bMaxPacketSize0}=="8"
    ATTRS{speed}=="12"
    ATTRS{busnum}=="2"
    ATTRS{devnum}=="2"
    ATTRS{devpath}=="2"
    ATTRS{version}==" 1.10"
    ATTRS{maxchild}=="0"
    ATTRS{quirks}=="0x0"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{authorized}=="1"
    ATTRS{serial}=="01402100A5000000"

  looking at parent device '/devices/pci0000:00/0000:00:1d.0/usb2':
    KERNELS=="usb2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bmAttributes}=="e0"
    ATTRS{bMaxPower}=="  0mA"
    ATTRS{urbnum}=="34"
    ATTRS{idVendor}=="1d6b"
    ATTRS{idProduct}=="0001"
    ATTRS{bcdDevice}=="0302"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{speed}=="12"
    ATTRS{busnum}=="2"
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{version}==" 1.10"
    ATTRS{maxchild}=="2"
    ATTRS{quirks}=="0x0"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{authorized}=="1"
    ATTRS{manufacturer}=="Linux 3.2.0-29-generic uhci_hcd"
    ATTRS{product}=="UHCI Host Controller"
    ATTRS{serial}=="0000:00:1d.0"
    ATTRS{authorized_default}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:1d.0':
    KERNELS=="0000:00:1d.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="uhci_hcd"
    ATTRS{vendor}=="0x8086"
    ATTRS{device}=="0x2658"
    ATTRS{subsystem_vendor}=="0x1043"
    ATTRS{subsystem_device}=="0x82d8"
    ATTRS{class}=="0x0c0300"
    ATTRS{irq}=="23"
    ATTRS{local_cpus}=="ff"
    ATTRS{local_cpulist}=="0-7"
    ATTRS{dma_mask_bits}=="32"
    ATTRS{consistent_dma_mask_bits}=="32"
    ATTRS{broken_parity_status}=="0"
    ATTRS{msi_bus}==""

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

jjk@eee-old:~$ 

И протестировал настройку:

sudo udevadm --debug test /sys/class/video4linux/video1

main: runtime dir '/run/udev'
run_command: calling: test
adm_test: version 175
This program is for debugging only, it does not run any program,
specified by a RUN key. It may show incorrect results, because
some values may be different, or not available at a simulation run.

parse_file: reading '/lib/udev/rules.d/40-crda.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-fuse.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-gnupg.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-hplip.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-ia64.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-inputattach.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-libgphoto2-2.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-libsane.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-ppc.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-usb_modeswitch.rules' as rules file
parse_file: reading '/lib/udev/rules.d/40-xserver-xorg-video-intel.rules' as rules file
parse_file: reading '/lib/udev/rules.d/42-qemu-usb.rules' as rules file
parse_file: reading '/lib/udev/rules.d/50-firmware.rules' as rules file
parse_file: reading '/lib/udev/rules.d/50-udev-default.rules' as rules file
parse_file: reading '/lib/udev/rules.d/55-dm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/56-hpmud_support.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-cdrom_id.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-pcmcia.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-alsa.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-input.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-serial.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-storage-dm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-storage-tape.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-storage.rules' as rules file
parse_file: reading '/lib/udev/rules.d/60-persistent-v4l.rules' as rules file
parse_file: reading '/lib/udev/rules.d/61-accelerometer.rules' as rules file
parse_file: reading '/lib/udev/rules.d/64-xorg-xkb.rules' as rules file
parse_file: reading '/lib/udev/rules.d/66-xorg-synaptics-quirks.rules' as rules file
parse_file: reading '/lib/udev/rules.d/69-cd-sensors.rules' as rules file
add_rule: IMPORT found builtin 'usb_id', replacing /lib/udev/rules.d/69-cd-sensors.rules:76
parse_file: reading '/lib/udev/rules.d/69-libmtp.rules' as rules file
parse_file: reading '/lib/udev/rules.d/69-xorg-vmmouse.rules' as rules file
parse_file: reading '/lib/udev/rules.d/69-xserver-xorg-input-wacom.rules' as rules file
parse_file: reading '/etc/udev/rules.d/70-persistent-cd.rules' as rules file
parse_file: reading '/etc/udev/rules.d/70-persistent-net.rules' as rules file
parse_file: reading '/lib/udev/rules.d/70-printers.rules' as rules file
parse_file: reading '/lib/udev/rules.d/70-udev-acl.rules' as rules file
parse_file: reading '/lib/udev/rules.d/75-cd-aliases-generator.rules' as rules file
parse_file: reading '/lib/udev/rules.d/75-net-description.rules' as rules file
parse_file: reading '/lib/udev/rules.d/75-persistent-net-generator.rules' as rules file
parse_file: reading '/lib/udev/rules.d/75-probe_mtd.rules' as rules file
parse_file: reading '/lib/udev/rules.d/75-tty-description.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-ericsson-mbm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-longcheer-port-types.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-nokia-port-types.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-pcmcia-device-blacklist.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-platform-serial-whitelist.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-qdl-device-blacklist.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-simtech-port-types.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-usb-device-blacklist.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-x22x-port-types.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-mm-zte-port-types.rules' as rules file
parse_file: reading '/lib/udev/rules.d/77-nm-olpc-mesh.rules' as rules file
parse_file: reading '/lib/udev/rules.d/78-graphics-card.rules' as rules file
parse_file: reading '/lib/udev/rules.d/78-sound-card.rules' as rules file
parse_file: reading '/lib/udev/rules.d/80-drivers.rules' as rules file
parse_file: reading '/lib/udev/rules.d/80-mm-candidate.rules' as rules file
parse_file: reading '/lib/udev/rules.d/80-udisks.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-brltty.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-hdparm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-hplj10xx.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-keyboard-configuration.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-regulatory.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-usbmuxd.rules' as rules file
parse_file: reading '/lib/udev/rules.d/90-alsa-restore.rules' as rules file
parse_file: reading '/lib/udev/rules.d/90-alsa-ucm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/90-libgpod.rules' as rules file
parse_file: reading '/lib/udev/rules.d/90-pulseaudio.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-cd-devices.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-keyboard-force-release.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-keymap.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-udev-late.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-dell.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-fujitsu.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-gateway.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-ibm.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-lenovo.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-battery-recall-toshiba.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-csr.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-hid.rules' as rules file
parse_file: reading '/lib/udev/rules.d/95-upower-wup.rules' as rules file
parse_file: reading '/lib/udev/rules.d/97-bluetooth-hid2hci.rules' as rules file
parse_file: reading '/etc/udev/rules.d/jj-video.rules' as rules file
udev_rules_new: rules use 259284 bytes tokens (21607 * 12 bytes), 37913 bytes buffer
udev_rules_new: temporary index used 67520 bytes (3376 * 20 bytes)
udev_device_new_from_syspath: device 0x215103e0 has devpath '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0/video4linux/video1'
udev_device_new_from_syspath: device 0x21510758 has devpath '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0/video4linux/video1'
udev_device_read_db: device 0x21510758 filled with db file data
udev_device_new_from_syspath: device 0x21510e10 has devpath '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0'
udev_device_new_from_syspath: device 0x21511b10 has devpath '/devices/pci0000:00/0000:00:1d.0/usb2/2-2'
udev_device_new_from_syspath: device 0x215132f8 has devpath '/devices/pci0000:00/0000:00:1d.0/usb2'
udev_device_new_from_syspath: device 0x21513650 has devpath '/devices/pci0000:00/0000:00:1d.0'
udev_device_new_from_syspath: device 0x21513980 has devpath '/devices/pci0000:00'
udev_rules_apply_to_event: GROUP 44 /lib/udev/rules.d/50-udev-default.rules:29
udev_rules_apply_to_event: IMPORT 'v4l_id /dev/video1' /lib/udev/rules.d/60-persistent-v4l.rules:7
udev_event_spawn: starting 'v4l_id /dev/video1'
spawn_read: 'v4l_id /dev/video1'(out) 'ID_V4L_VERSION=2'
spawn_read: 'v4l_id /dev/video1'(out) 'ID_V4L_PRODUCT=Logitech QuickCam Pro 3000'
spawn_read: 'v4l_id /dev/video1'(out) 'ID_V4L_CAPABILITIES=:capture:'
spawn_wait: 'v4l_id /dev/video1' [2609] exit with return code 0
udev_rules_apply_to_event: IMPORT builtin 'usb_id' /lib/udev/rules.d/60-persistent-v4l.rules:9
builtin_usb_id: /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0: if_class 10 protocol 0
udev_builtin_add_property: ID_VENDOR=046d
udev_builtin_add_property: ID_VENDOR_ENC=046d
udev_builtin_add_property: ID_VENDOR_ID=046d
udev_builtin_add_property: ID_MODEL=08b0
udev_builtin_add_property: ID_MODEL_ENC=08b0
udev_builtin_add_property: ID_MODEL_ID=08b0
udev_builtin_add_property: ID_REVISION=0002
udev_builtin_add_property: ID_SERIAL=046d_08b0_01402100A5000000
udev_builtin_add_property: ID_SERIAL_SHORT=01402100A5000000
udev_builtin_add_property: ID_TYPE=generic
udev_builtin_add_property: ID_BUS=usb
udev_builtin_add_property: ID_USB_INTERFACES=:0aff00:010100:010200:
udev_builtin_add_property: ID_USB_INTERFACE_NUM=00
udev_builtin_add_property: ID_USB_DRIVER=Philips webcam
udev_rules_apply_to_event: LINK 'v4l/by-id/usb-046d_08b0_01402100A5000000-video-index0' /lib/udev/rules.d/60-persistent-v4l.rules:10
udev_rules_apply_to_event: IMPORT builtin 'path_id' /lib/udev/rules.d/60-persistent-v4l.rules:16
udev_builtin_add_property: ID_PATH=pci-0000:00:1d.0-usb-0:2:1.0
udev_builtin_add_property: ID_PATH_TAG=pci-0000_00_1d_0-usb-0_2_1_0
udev_rules_apply_to_event: LINK 'v4l/by-path/pci-0000:00:1d.0-usb-0:2:1.0-video-index0' /lib/udev/rules.d/60-persistent-v4l.rules:17
udev_rules_apply_to_event: RUN 'udev-acl --action=$env{ACTION} --device=$env{DEVNAME}' /lib/udev/rules.d/70-udev-acl.rules:74
udev_rules_apply_to_event: LINK 'webcam1' /etc/udev/rules.d/jj-video.rules:2
udev_event_execute_rules: no node name set, will use kernel supplied name 'video1'
udev_node_add: creating device node '/dev/video1', devnum=81:1, mode=0660, uid=0, gid=44
udev_node_mknod: preserve file '/dev/video1', because it has correct dev_t
udev_node_mknod: preserve permissions /dev/video1, 020660, uid=0, gid=44
node_symlink: preserve already existing symlink '/dev/char/81:1' to '../video1'
link_find_prioritized: found 'c81:2' claiming '/run/udev/links/v4l\x2fby-id\x2fusb-046d_08b0_01402100A5000000-video-index0'
udev_device_new_from_syspath: device 0x21516748 has devpath '/devices/pci0000:00/0000:00:1d.1/usb3/3-2/3-2:1.0/video4linux/video2'
udev_device_read_db: device 0x21516748 filled with db file data
link_find_prioritized: found 'c81:1' claiming '/run/udev/links/v4l\x2fby-id\x2fusb-046d_08b0_01402100A5000000-video-index0'
link_update: creating link '/dev/v4l/by-id/usb-046d_08b0_01402100A5000000-video-index0' to '/dev/video1'
node_symlink: atomically replace '/dev/v4l/by-id/usb-046d_08b0_01402100A5000000-video-index0'
link_find_prioritized: found 'c81:1' claiming '/run/udev/links/v4l\x2fby-path\x2fpci-0000:00:1d.0-usb-0:2:1.0-video-index0'
link_update: creating link '/dev/v4l/by-path/pci-0000:00:1d.0-usb-0:2:1.0-video-index0' to '/dev/video1'
node_symlink: preserve already existing symlink '/dev/v4l/by-path/pci-0000:00:1d.0-usb-0:2:1.0-video-index0' to '../../video1'
link_find_prioritized: found 'c81:1' claiming '/run/udev/links/webcam1'
link_update: creating link '/dev/webcam1' to '/dev/video1'
node_symlink: preserve already existing symlink '/dev/webcam1' to 'video1'
udev_device_update_db: created db file '/run/udev/data/c81:1' for '/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0/video4linux/video1'
ACTION=add
COLORD_DEVICE=1
COLORD_KIND=camera
DEVLINKS=/dev/v4l/by-id/usb-046d_08b0_01402100A5000000-video-index0 /dev/v4l/by-path/pci-0000:00:1d.0-usb-0:2:1.0-video-index0 /dev/webcam1
DEVNAME=/dev/video1
DEVPATH=/devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0/video4linux/video1
ID_BUS=usb
ID_MODEL=08b0
ID_MODEL_ENC=08b0
ID_MODEL_ID=08b0
ID_PATH=pci-0000:00:1d.0-usb-0:2:1.0
ID_PATH_TAG=pci-0000_00_1d_0-usb-0_2_1_0
ID_REVISION=0002
ID_SERIAL=046d_08b0_01402100A5000000
ID_SERIAL_SHORT=01402100A5000000
ID_TYPE=generic
ID_USB_DRIVER=Philips webcam
ID_USB_INTERFACES=:0aff00:010100:010200:
ID_USB_INTERFACE_NUM=00
ID_V4L_CAPABILITIES=:capture:
ID_V4L_PRODUCT=Logitech QuickCam Pro 3000
ID_V4L_VERSION=2
ID_VENDOR=046d
ID_VENDOR_ENC=046d
ID_VENDOR_ID=046d
MAJOR=81
MINOR=1
SUBSYSTEM=video4linux
TAGS=:udev-acl:
UDEV_LOG=6
USEC_INITIALIZED=18213768
run: 'udev-acl --action=add --device=/dev/video1'
jjk@eee-old:~$ 

(и соответственно для video2)

Мне кажется, что мои правила прочитаны, но не соблюдаются. Что я делаю не так?