Making udev rule to set usb device permissions
From Finninday
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_nod_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.
