APC SU1400XLT User Manual download pdf (Page 15)

Modern Linux distributions using the 2.6 kernel create device nodes dynamically on the fly as they are

needed. It is basically a hotplug system, giving a lot more power to the user to determine what happens

when a device is probed or opened. It is also a lot more complicated.

Some early 2.6 distributions (Fedora Core 3, for one) do not include hiddev rules in their default udev rule

set. The bottom line for apcupsd on such a system is that if the hiddevN is not created when you plug in

your UPS, apcupsd will terminate with an error. The solution to the problem is to add a rule to the udev

rules file. On Fedora FC3, this file is found in /etc/udev/rules.d/50-udev.rules. Start by adding

the following line:

BUS="usb", SYSFS{idVendor}="051d", NAME="usb/hiddev%n"

Note that this rule uses obsolete udev syntax and is specific to FC3 and other distributions of similar

vintage.

Then either reboot your system, or unplug and replug your UPS and then restart apcupsd. At that point a

/dev/usb/hiddevN node should appear and apcupsd should work fine.

If you have several UPSes or you just want to give your UPS a fixed name, you can use rules like the

following:

KERNEL=="hiddev*", SYSFS{serial}=="JB0319033692", SYMLINK="ups0"

KERNEL=="hiddev*", SYSFS{serial}=="JB0320004845", SYMLINK="ups1"

Note that this rule uses udev syntax that is appropriate only for distros such as RHEL4 and FC4 and

others of a similar vintage.

More recent distros such as FC15 should use something like this:

KERNEL=="hiddev*", ATTRS{manufacturer}=="American Power Conversion", ATTRS{serial}=="BB0100009999 ", OWNER="root", SYMLINK+="ups0"

Replace the serial number in quotes with the one that corresponds to your UPS. Then whenever you plug

in your UPS a symlink called ups0, ups1, etc. will be created pointing to the correct hiddev node. This

technique is highly recommended if you have more than one UPS connected to the same server since

rearranging your USB cables or even upgrading the kernel can affect the order in which devices are

detected and thus change which hiddev node corresponds to which UPS. If you use the

symlink-by-serial-number approach the link will always point to the correct device node.

You can use...

udevinfo -a -p /sys/class/usb/hiddev0/

...to get more information on the fields that can be matched besides serial number.

To find the available attributes to match (note that the serial is NOT always the UPS serial on the box or in

the USB connect message in /var/log/messages), use:

udevadm info --attribute-walk --name=/dev/usb/hiddev0

An additional device-node-related problem is the use of dynamic minors. Some distributions, such as

Mandrake 10, ship with a kernel having CONFIG_USB_DYNAMIC_MINORS turned on. This is not ideal for

running with apcupsd, and the easiest solution is to turn CONFIG_USB_DYNAMIC_MINORS off and rebuild

your kernel, or find a pre-built kernel with it off. For a kernel with CONFIG_USB_DYNAMIC_MINORS turned

on to work with apcupsd, you must enable devfs. The following will tell you if devfs is enabled:

$ ps ax | grep devs

...which should give something like the following:

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 114 115

No comments

APC SU1400XLT User Manual Page 15