Gfrktyl

I have Ubuntu Server 14.04.1 LTS running in a Hyper-V virtual machine on a Windows 2012 R2 host.

After running for some time, the Ubuntu server seems to freeze up (at least partially). A website it's hosting under nginx stops working. I can connect via Putty and enter my username and password, but then the session immediately hangs:

The same thing happens when I try to log in from the console (making it difficult to check logs / troubleshoot). However I do notice output like this sitting in the console window:

If there is a local or remote console session that is already logged in, I can still interact with it. However any attempt to write to the disk freezes the session.

I managed to snag a dmesg dump and recent content of kernel.log. And here's an earlier, partial dmesg screencap in case it is of use.

I believe the issue may be related to the disk I/O stack:

[16209.927138] hv_storvsc vmbus_0_13: cmd 0x35 scsi status 0x2 srb status 0x82

[16209.927142] hv_storvsc vmbus_0_13: stor pkt ffff88003b203100 autosense data valid - len 18

[16209.927144] storvsc: Sense Key : Unit Attention [current]

[16209.927146] storvsc: Add. Sense: Changed operating definition

[16209.927151] sd 0:0:0:0: Warning! Received an indication that the operating parameters on this target have changed. The Linux SCSI layer does not automatically adjust these parameters.

[45841.680551] INFO: task rs:main Q:Reg:882 blocked for more than 120 seconds.

[45841.680580]       Not tainted 3.13.0-32-generic #57-Ubuntu

[45841.680596] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

The install is fairly fresh and default settings were accepted for pretty much everything. The VM is using Hyper-V's "generation 2" guest architecture, with secure boot disabled.

My symptoms seem similar to those reported here, here and here, but those threads are a few years old and refer to older versions of guest & host.

The server still responds to pings. Also note we saw the freezing behavior before nginx was installed.

I don't think it's a resource issue. The VM has 1GB of RAM and plenty of disk space. Here's what things look like before it freezes:

  System information as of Sun Aug  3 16:03:30 EDT 2014



  System load:  0.08              Processes:           231

  Usage of /:   3.6% of 96.59GB   Users logged in:     1

  Memory usage: 29%               IP address for eth0: 172.22.0.26

  Swap usage:   0%

I'm looking for:

1. Tips on how to efficiently troubleshoot this




2. Instructions on how to turn off any sort of disk-related features (e.g. power saving) that came out of the box in my Ubuntu install.




3. A recommendation on where to find a Linux + Hyper-V genius we can hire remotely to help sort this out (and maybe other occasional Linux work)

I found an info in the French Ubuntu forums from other user who has Ubuntu freezes: It may be caused by "dynamic tick".

Their solution:

cd /etc/default

sudo vi grub

add nohz=true in parameters of the line GRUB_CMDLINE_LINUX_DEFAULT. Then do a

sudo grub-update

I think I also have this problem – have you found this:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1470250