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We were looking at the behavior of hald on a Linux host (Ubuntu 12.04.2 LTS 64-bit). We looked at both its syslog and system calls (using strace). According to the ...
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  1. #1
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    hald (HAL daemon) behavior analysis


    We were looking at the behavior of hald on a Linux host (Ubuntu 12.04.2 LTS 64-bit). We looked at both its syslog and system calls (using strace). According to the documentation, hald receives notifications whenever a new hardware device is plugged in. On our host, however, even though we never plug in any new hardware devices, the hald process keeps receiving messages from a datagram unix domain socket (which was bound at /org/freedesktop/hal/udev_event). From syslog, we can see the repeated messages such as this:

    hald[19608]: 22:26:33.665 [I] osspec.c:256: SEQNUM=541371, ACTION=add, SUBSYSTEM=queues, DEVPATH=/sys/devices/virtual/net/lo/queues/rx-0, DEVNAME=, IFINDEX=0
    hald[19608]: 22:26:33.665 [D] hotplug.c:476: checking ADD event /sys/devices/virtual/net/lo/queues/rx-0

    hald[19608]: 22:26:33.665 [D] hotplug.c:397: event /sys/devices/virtual/net/lo/queues/rx-0: skip ourselves and all later events

    hald[19608]: 22:26:33.665 [I] osspec.c:1022: hal_util_find_known_parent: '/sys/devices/virtual/net/lo/queues/rx-0/sys/devices/virtual/net/lo'

    hald[19608]: 22:26:33.665 [I] device.c:4997: add_dev: subsys=queues sysfs_path=/sys/devices/virtual/net/lo/queues/rx-0 dev= parent_dev=0x01d66980

    hald[19608]: 22:26:33.665 [D] hotplug.c:500: events queued = 0, events in progress = 0

    hald[19608]: 22:26:33.665 [D] hotplug.c:505: Hotplug-queue empty now ... no hotplug events in progress
    I wonder what is this really happening. It seems that some one has requested the device "/sys/devices/virtual/net/lo/queues/rx-0" to be added to the system. However, this path already existed (thus I assume added already) and I do not understand why someone keeps asking to add it. We are suspecting that something is wrong in the system and such requests should not be generated in the first place (but couldn't confirm). If anyone could shed any light on such behavior, it will be very appreciated!

  2. #2
    Linux Engineer
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    Dec 2013
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    1,305
    I don't know for sure but lo is the loopback device - a virtual network interface used for localhost so you could see this any time a process is opening a local socket. queue/rx-0 refers to the network send/receive queue for processor 0 I believe. Note that it's a virtual device.

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