Writing udev rules, short notes
Today I was connecting a second USB harddrive to my NSLU2.
What you get is a few interesting effects, among them device IDs (/dev/sda, sdb…) changing depending on the order in which you attach the drives. Plus, I added a USB hub, which makes the device names change anyway.
The solution for the crazily jumping dev nodes is the udev system, which is part of Linux for quite a while now, but I never really had a need to play with it yet. But the howto is pretty nice and easy to apply.
Still, a few notes:
- The
SYSFS{whatever}rules support wildcards, so that you don’t have to write the whole descriptor if you don’t want to. For example, “Max*” instead of “Maxtor 6” works totally fine. — That’s especially useful sinceSYSFS{model}descriptors often seem to be filled up with a couple of spaces at the end. - Some (all?) USB hard drives in fact don’t consider themselves to be USB devices. So in this case defining
BUS=="usb"will not result in any device links to be created at all. I had to defineBUS=="scsi"instead. You should look at theudevinfooutput as suggested in the “writing udev rules” howto, it will tell you exactly what setup is necessary for your device/drive configuration.
That’s how my two new rules look like (each in one line only):
BUS==”scsi”, KERNEL==”sd*”, SYSFS{vendor}==”Maxtor*”, SYSFS{model}==”L250R0*”, NAME=”%k”, SYMLINK=”usbhd/maxtor250%n”
BUS==”scsi”, KERNEL==”sd*”, SYSFS{vendor}==”Maxtor*”, SYSFS{model}==”Y080P0*”, NAME=”%k”, SYMLINK=”usbhd/maxtor80%n”
If you have any questions, let me know.
If not, have fun 
March 19th, 2006 at 1:20 pm
Another (possibly easier) way to get at the disk you want is to use ext2 labels. You give a filesystem a label, and then refer to it during mounting via the label instead of the device name. This also survives if you have to replace the machine/OS; the label info is stored in the filesystem itself, whereas the udev conf is specific to that OS instance.
Of course, if you’re not using ext2 (or ext3), you can’t use ext2 labels.
Yet another way to overcome devices switching about might be to use LVM. This isn’t quite as transparent as ext2 labels, tho. You’ll have to activate volume groups when you plug in drives. It’ll be transparent across reboots and OS’s, though.
– Dan
March 19th, 2006 at 1:41 pm
Dan, thanks for the additional info. I like the idea to use device labels. While udev rules are perfect for USB printers / scanners etc., for mounting block devices instead, the label solution seems to be much easier.
June 19th, 2007 at 1:29 am
if i want to run a particular application whenever an USB is plugged, what i have to do with udev and how can i write its rules?
June 19th, 2007 at 1:40 am
Zoobave: You want to read the udev howto to find that out. It is very detailed and shows you what udev can do and how you can make it do what you want.
June 19th, 2007 at 4:39 am
i did, but, i couldn’t understand where to write . my program is in “/usr/local/zoobave/start”.
i want to start this application, whenever i insert any USB devices. Where i put these entries? is their any need to restart or reload udev?
June 19th, 2007 at 6:52 am
The rules files live in /etc/udev/rules.d, as written in the “files” part of the howto.
And yes you will need to reload the udev rules (or reboot if you like), which they describe in the testing section. Hope this helps!
June 19th, 2007 at 10:24 pm
finally, i put the following entry in “/etc/udev/rules.d/01-local.rules” file.
SUBSYSTEM==”usb_device”, ACTION==”add”, ATTRS{manufacturer}==”JetFlash”, PROGRAM=”/usr/bin/nautilus ”, NAME=”%c”, MODE=”0777″
if i test using then following command, the nautilus starts
dvm@dvm-desktop:~$ udevtest /sys/class/usb_device/usbdev4.5/
parse_file: reading ‘/etc/udev/rules.d/00- init.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/01-local.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/05-options.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/10- myrule.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/20-names.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/25-dmsetup.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/25- iftab.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/30-cdrom_id.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/40-permissions.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/45- fuse.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/45-hplip.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/45-libgphoto2.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/45- libsane.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/50-xserver-xorg-input-wacom.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/60-libpisock.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/60- symlinks.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/65-persistent-input.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/65-persistent-storage.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/80-programs.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-alsa.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-brltty.rules ‘ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-hdparm.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-hplj10xx.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-hwclock.rules ‘ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-ifupdown.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/85-pcmcia.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/90- modprobe.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/95-hal.rules’ as rules file
parse_file: reading ‘/etc/udev/rules.d/99-udevmonitor.rules’ as rules file
This program is for debugging only, it does not run any program,
specified by a RUN key. It may show incorrect results, if rules
match against subsystem specfic kernel event variables.
main: looking at device ‘/class/usb_device/usbdev4.5′ from subsystem ‘usb_device’
run_program: ‘/usr/bin/nautilus ‘
run_program: ‘/usr/bin/nautilus’ returned with status 0
udev_rules_get_name: rule applied, ‘usbdev4.5′ becomes ‘’
run_program: ‘usb_device_name –export usbdev4.5′
run_program: ‘/lib/udev/usb_device_name’ (stdout) ‘USB_BUS=004′
run_program: ‘/lib/udev/usb_device_name’ (stdout) ‘USB_DEV=005′
run_program: ‘/lib/udev/usb_device_name’ returned with status 0
run_program: ‘check_ptp_camera 06/01/01′
run_program: ‘/lib/udev/check_ptp_camera’ returned with status 1
udev_device_event: device node creation supressed
main: run: ’socket:/org/freedesktop/hal/udev_event’
main: run: ’socket:/org/kernel/udev/monitor’
but, when i insert the same device, it will not run the program automatically. How can i modify the above entry to run the nautilus (or any program) automatically?
November 17th, 2007 at 8:44 pm
I have been fighting udev for a while, and can not figure out how to write a udev rule that works with ppp0. In order to access the Internet, I manually entered: ln -s /dev/ppp /dev/ppp0
Thank you, Walt
March 13th, 2008 at 9:12 am
Zoobave, replace PROGRAM==”/path/to/prog” with RUN+=”/path/to/prog” and it should work given that your other matching rules are in place. Don’t forget to reload the config either.