Difference between revisions of "Making udev rule to set usb device permissions"

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(→‎making a rule)
(→‎making a rule)
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So I put that in my rule file and run udevadm test again.
 
So I put that in my rule file and run udevadm test again.
 +
 +
OK, that didn't work either, but it turns out this simple rule does work:
 +
 +
  KERNEL=="ldusb0", MODE="644"
 +
 +
<pre>
 +
root@weasel:/etc/udev/rules.d# udevadm test /sys/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
 +
run_command: calling: test
 +
udevadm_test: version 163
 +
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-fuse-utils.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-kino.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-libpisock9.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-media-players.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-virtualbox-ose-dkms.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/41-mythtv-permissions.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/45-fuse.rules' as rules file
 +
parse_file: reading '/etc/udev/rules.d/45-libmtp7.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/45-libmtp8.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/56-lvm.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-floppy.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-lvm.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-gnome-bluetooth-rfkill.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/61-mobile-action.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/61-persistent-storage-edd.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.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 '/lib/udev/rules.d/70-acl.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/70-hid2hci.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/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-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-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-zte-port-types.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/79-fstab_import.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/80-alsa.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-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-console-setup.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-lvm2.rules' as rules file
 +
parse_file: reading '/lib/udev/rules.d/85-pcmcia.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-hal.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 '/etc/udev/rules.d/90-vernier.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.rules' as rules file
 +
parse_file: reading '/dev/.udev/rules.d/root.rules' as rules file
 +
udev_rules_new: rules use 252972 bytes tokens (21081 * 12 bytes), 36755 bytes buffer
 +
udev_rules_new: temporary index used 61220 bytes (3061 * 20 bytes)
 +
udev_device_new_from_syspath: device 0x7f0eddcffd50 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
 +
udev_device_new_from_syspath: device 0x7f0eddcf01b0 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
 +
udev_device_read_db: device 0x7f0eddcf01b0 filled with db symlink data '/dev/ldusb0'
 +
udev_device_new_from_syspath: device 0x7f0eddd08b80 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0'
 +
udev_device_new_from_syspath: device 0x7f0eddd08e70 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8'
 +
udev_device_new_from_syspath: device 0x7f0eddd09180 has devpath '/devices/pci0000:00/0000:00:02.0/usb2'
 +
udev_device_new_from_syspath: device 0x7f0eddd09480 has devpath '/devices/pci0000:00/0000:00:02.0'
 +
udev_device_new_from_syspath: device 0x7f0eddd09750 has devpath '/devices/pci0000:00'
 +
udev_rules_apply_to_event: LINK 'char/180:176' /lib/udev/rules.d/50-udev-default.rules:4
 +
udev_rules_apply_to_event: RUN 'socket:@/org/freedesktop/hal/udev_event' /lib/udev/rules.d/90-hal.rules:2
 +
udev_rules_apply_to_event: MODE 0644 /etc/udev/rules.d/90-vernier.rules:4
 +
udev_event_execute_rules: no node name set, will use kernel supplied name 'ldusb0'
 +
udev_device_update_db: created db link (ldusb0 char/180:176)
 +
udev_node_add: creating device node '/dev/ldusb0', devnum=180:176, mode=0644, uid=0, gid=0
 +
udev_node_mknod: preserve file '/dev/ldusb0', because it has correct dev_t
 +
udev_node_mknod: set permissions /dev/ldusb0, 020644, uid=0, gid=0
 +
node_symlink: preserve already existing symlink '/dev/char/180:176' to '../ldusb0'
 +
udevadm_test: UDEV_LOG=6
 +
udevadm_test: DEVPATH=/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
 +
udevadm_test: MAJOR=180
 +
udevadm_test: MINOR=176
 +
udevadm_test: DEVNAME=/dev/ldusb0
 +
udevadm_test: ACTION=add
 +
udevadm_test: SUBSYSTEM=usb
 +
udevadm_test: DEVLINKS=/dev/char/180:176
 +
udevadm_test: run: 'socket:@/org/freedesktop/hal/udev_event'
 +
</pre>

Revision as of 18:00, 22 December 2010

I have a USB temperature probe that defaults to 600 permission and ownership by root. I'd like everyone (especially my non-root script) to be able to read this device, so I set it to 644 permission. But something keeps switching the permission back. I assume this something is udev. To make my permission setting stick, I told udev to honor it by creating this file: 

root@weasel:/etc/udev/rules.d# pwd;ls
/etc/udev/rules.d
45-libmtp7.rules	70-persistent-net.rules  README
70-persistent-cd.rules	99-vernier.rules
root@weasel:/etc/udev/rules.d# cat 99-vernier.rules 
# Vernier EasyTemp/Go!Temp
ATTR{idVendor}=="08f7", ATTR{idProduct}=="0002", MODE="644"

I guessed at the syntax by peeking at the other rules files in this directory.

My previous attempt at a fix for this was to add a "chmod" to /etc/rc.local, but udev is smarter than that, since it changes the permission of my usb device at times other than reboot. We'll see if this udev rule is sufficient. If not, I'll have to start reading more about udev.

I disabled the /etc/rc.local script and rebooted... immediately after booting, the permissions on /dev/ldusb0 were 600 again.

Bummer.

udevadm query

OK, getting a little more serious about understanding udev, I am starting with this document: http://reactivated.net/writing_udev_rules.html

And I also learn that the udevinfo command doesn't exist in Ubuntu, but there does exist a udevadm command and it works like this: 

root@weasel:/sys/dev/char# udevadm info -q all -n /dev/ldusb0
P: /devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
N: ldusb0
S: char/180:176
E: UDEV_LOG=3
E: DEVPATH=/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
E: SUBSYSTEM=usb
E: DEVNAME=/dev/ldusb0
E: MAJOR=180
E: MINOR=176
E: DEVLINKS=/dev/char/180:176

That's cool, but where is the corresponding program "udevtest"? Ahh it is also in udevadm: 

root@weasel:/sys/dev/char# udevadm test /sys/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
run_command: calling: test
udevadm_test: version 163
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-fuse-utils.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-kino.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-libpisock9.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-media-players.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-virtualbox-ose-dkms.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/41-mythtv-permissions.rules' as rules file
parse_file: reading '/lib/udev/rules.d/45-fuse.rules' as rules file
parse_file: reading '/etc/udev/rules.d/45-libmtp7.rules' as rules file
parse_file: reading '/lib/udev/rules.d/45-libmtp8.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/56-lvm.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-floppy.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-lvm.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-gnome-bluetooth-rfkill.rules' as rules file
parse_file: reading '/lib/udev/rules.d/61-mobile-action.rules' as rules file
parse_file: reading '/lib/udev/rules.d/61-persistent-storage-edd.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.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 '/lib/udev/rules.d/70-acl.rules' as rules file
parse_file: reading '/lib/udev/rules.d/70-hid2hci.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/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-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-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-zte-port-types.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/79-fstab_import.rules' as rules file
parse_file: reading '/lib/udev/rules.d/80-alsa.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-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-console-setup.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-lvm2.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-pcmcia.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-hal.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-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.rules' as rules file
parse_file: reading '/etc/udev/rules.d/99-vernier.rules' as rules file
parse_file: reading '/dev/.udev/rules.d/root.rules' as rules file
udev_rules_new: rules use 252984 bytes tokens (21082 * 12 bytes), 36753 bytes buffer
udev_rules_new: temporary index used 61220 bytes (3061 * 20 bytes)
udev_device_new_from_syspath: device 0x7fb328725d50 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
udev_device_new_from_syspath: device 0x7fb3287161b0 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
udev_device_read_db: device 0x7fb3287161b0 filled with db symlink data '/dev/ldusb0'
udev_device_new_from_syspath: device 0x7fb32872eb80 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0'
udev_device_new_from_syspath: device 0x7fb32872ee70 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8'
udev_device_new_from_syspath: device 0x7fb32872f180 has devpath '/devices/pci0000:00/0000:00:02.0/usb2'
udev_device_new_from_syspath: device 0x7fb32872f480 has devpath '/devices/pci0000:00/0000:00:02.0'
udev_device_new_from_syspath: device 0x7fb32872f750 has devpath '/devices/pci0000:00'
udev_rules_apply_to_event: LINK 'char/180:176' /lib/udev/rules.d/50-udev-default.rules:4
udev_rules_apply_to_event: RUN 'socket:@/org/freedesktop/hal/udev_event' /lib/udev/rules.d/90-hal.rules:2
udev_event_execute_rules: no node name set, will use kernel supplied name 'ldusb0'
udev_device_update_db: created db link (ldusb0 char/180:176)
udev_node_add: creating device node '/dev/ldusb0', devnum=180:176, mode=0600, uid=0, gid=0
udev_node_mknod: preserve file '/dev/ldusb0', because it has correct dev_t
udev_node_mknod: set permissions /dev/ldusb0, 020600, uid=0, gid=0
node_symlink: preserve already existing symlink '/dev/char/180:176' to '../ldusb0'
udevadm_test: UDEV_LOG=6
udevadm_test: DEVPATH=/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
udevadm_test: MAJOR=180
udevadm_test: MINOR=176
udevadm_test: DEVNAME=/dev/ldusb0
udevadm_test: ACTION=add
udevadm_test: SUBSYSTEM=usb
udevadm_test: DEVLINKS=/dev/char/180:176
udevadm_test: run: 'socket:@/org/freedesktop/hal/udev_event'

Hey, that shows me the culprit who keeps switching the permissions on this file to 600. Curse you, udev_node_mknod!

So I just need to create a rule that will run after udev_node_mknod and undo its mischief.

I also see that my rule file was parsed, but never triggered. Evidently because it did not match. It looks like only two rules matched: 50-udev-default and 90-hal.

making a rule

Rules are pretty simple: a series of matching pairs and an action pair. Matching pairs are coupled by the equivalence operator (==) and action pairs are coupled by the assignment operator (=). All matching pairs must be true for the rule to trigger.

I'm pretty sure that I want my action pair to be this: 

 MODE="644"

So I just have to figure out the right way to uniquely describe my device. My guess about idVendor and idProduct were taken from the lsusb command and that didn't work. The matching is done on the /sys filesystem tree, so I have to find a property in there to match on. The udevinfo output contains this likely suspect: 

 DEVNAME=/dev/ldusb0

The syntax of the HOWTO I'm reading is wildly different from what udevadm is telling me. So I'll base my syntax on the local udev manpage.

The most direct rule looks like the one matches the device path (/dev/ldusb0). I can use this because I'm trying to make a change late in the process, after the device has been established. So my rule might be this: 

 DEVPATH=="/dev/ldusb0", MODE="644"

So I put that in my rule file and run udevadm test again.

OK, that didn't work either, but it turns out this simple rule does work: 

 KERNEL=="ldusb0", MODE="644"

root@weasel:/etc/udev/rules.d# udevadm test /sys/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
run_command: calling: test
udevadm_test: version 163
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-fuse-utils.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-kino.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-libpisock9.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-media-players.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-virtualbox-ose-dkms.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/41-mythtv-permissions.rules' as rules file
parse_file: reading '/lib/udev/rules.d/45-fuse.rules' as rules file
parse_file: reading '/etc/udev/rules.d/45-libmtp7.rules' as rules file
parse_file: reading '/lib/udev/rules.d/45-libmtp8.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/56-lvm.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-floppy.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-lvm.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-gnome-bluetooth-rfkill.rules' as rules file
parse_file: reading '/lib/udev/rules.d/61-mobile-action.rules' as rules file
parse_file: reading '/lib/udev/rules.d/61-persistent-storage-edd.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.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 '/lib/udev/rules.d/70-acl.rules' as rules file
parse_file: reading '/lib/udev/rules.d/70-hid2hci.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/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-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-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-zte-port-types.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/79-fstab_import.rules' as rules file
parse_file: reading '/lib/udev/rules.d/80-alsa.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-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-console-setup.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-lvm2.rules' as rules file
parse_file: reading '/lib/udev/rules.d/85-pcmcia.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-hal.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 '/etc/udev/rules.d/90-vernier.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.rules' as rules file
parse_file: reading '/dev/.udev/rules.d/root.rules' as rules file
udev_rules_new: rules use 252972 bytes tokens (21081 * 12 bytes), 36755 bytes buffer
udev_rules_new: temporary index used 61220 bytes (3061 * 20 bytes)
udev_device_new_from_syspath: device 0x7f0eddcffd50 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
udev_device_new_from_syspath: device 0x7f0eddcf01b0 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0'
udev_device_read_db: device 0x7f0eddcf01b0 filled with db symlink data '/dev/ldusb0'
udev_device_new_from_syspath: device 0x7f0eddd08b80 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0'
udev_device_new_from_syspath: device 0x7f0eddd08e70 has devpath '/devices/pci0000:00/0000:00:02.0/usb2/2-8'
udev_device_new_from_syspath: device 0x7f0eddd09180 has devpath '/devices/pci0000:00/0000:00:02.0/usb2'
udev_device_new_from_syspath: device 0x7f0eddd09480 has devpath '/devices/pci0000:00/0000:00:02.0'
udev_device_new_from_syspath: device 0x7f0eddd09750 has devpath '/devices/pci0000:00'
udev_rules_apply_to_event: LINK 'char/180:176' /lib/udev/rules.d/50-udev-default.rules:4
udev_rules_apply_to_event: RUN 'socket:@/org/freedesktop/hal/udev_event' /lib/udev/rules.d/90-hal.rules:2
udev_rules_apply_to_event: MODE 0644 /etc/udev/rules.d/90-vernier.rules:4
udev_event_execute_rules: no node name set, will use kernel supplied name 'ldusb0'
udev_device_update_db: created db link (ldusb0 char/180:176)
udev_node_add: creating device node '/dev/ldusb0', devnum=180:176, mode=0644, uid=0, gid=0
udev_node_mknod: preserve file '/dev/ldusb0', because it has correct dev_t
udev_node_mknod: set permissions /dev/ldusb0, 020644, uid=0, gid=0
node_symlink: preserve already existing symlink '/dev/char/180:176' to '../ldusb0'
udevadm_test: UDEV_LOG=6
udevadm_test: DEVPATH=/devices/pci0000:00/0000:00:02.0/usb2/2-8/2-8:1.0/usb/ldusb0
udevadm_test: MAJOR=180
udevadm_test: MINOR=176
udevadm_test: DEVNAME=/dev/ldusb0
udevadm_test: ACTION=add
udevadm_test: SUBSYSTEM=usb
udevadm_test: DEVLINKS=/dev/char/180:176
udevadm_test: run: 'socket:@/org/freedesktop/hal/udev_event'
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