Docker commands do not respond anymore

Question

Most of docker commands never end. I have to interrupt them manually with CTRL+C. Even simple commands like docker ps or docker info do not respond.

However, docker help and docker version still work.

I think there is something like a deadlock with a particular container, so commands related to containers won't complete.

How to handle such a situation ?

---

My docker version is 1.12.3. I don't use Swarm mode. The docker logs command doesn't work too. Using dmesg I can see a lot of I/O errors, but I don't know if it is related with my problem:

[12898.121287] loop: Write error at byte offset 8882749440, length 4096.
[12898.122837] loop: Write error at byte offset 8883666944, length 4096.
[12898.124685] loop: Write error at byte offset 8882814976, length 4096.
[12898.126459] loop: Write error at byte offset 8883404800, length 4096.
[12898.128201] loop: Write error at byte offset 8883470336, length 4096.
[12898.129921] loop: Write error at byte offset 8883535872, length 4096.
[12898.131774] loop: Write error at byte offset 8883601408, length 4096.
[12898.133594] loop: Write error at byte offset 8883732480, length 4096.
[12917.269786] loop: Write error at byte offset 8883798016, length 4096.
[12917.270331] quiet_error: 632 callbacks suppressed
[12917.270334] Buffer I/O error on device dm-6, logical block 1313320
[12917.270540] lost page write due to I/O error on dm-6
[12917.270543] Buffer I/O error on device dm-6, logical block 1313321
[12917.270740] lost page write due to I/O error on dm-6
[12917.270742] Buffer I/O error on device dm-6, logical block 1313322
[12917.270957] lost page write due to I/O error on dm-6
[12917.270959] Buffer I/O error on device dm-6, logical block 1313323
[12917.271177] lost page write due to I/O error on dm-6
[12917.271179] Buffer I/O error on device dm-6, logical block 1313324
[12917.271377] lost page write due to I/O error on dm-6
[12917.271379] Buffer I/O error on device dm-6, logical block 1313325
[12917.271573] lost page write due to I/O error on dm-6
[12917.301759] loop: Write error at byte offset 8883863552, length 4096.
[12917.312038] loop: Write error at byte offset 8883929088, length 4096.
[12917.312396] Buffer I/O error on device dm-6, logical block 1313328
[12917.312635] lost page write due to I/O error on dm-6
[12917.312638] Buffer I/O error on device dm-6, logical block 1313329
[12917.312867] lost page write due to I/O error on dm-6
[12917.312869] Buffer I/O error on device dm-6, logical block 1313330
[12917.313121] lost page write due to I/O error on dm-6
[12917.313123] Buffer I/O error on device dm-6, logical block 1313331
[12917.313346] lost page write due to I/O error on dm-6
[13090.853726] INFO: task kworker/u8:0:17212 blocked for more than 120 seconds.
[13090.854055] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

Using the command sudo systemctl status -l docker, the following messages are printed, but I cannot tell if they are related:

dockerd[1344]: time="2016-11-24T17:49:01.184874648+01:00" level=warning msg="libcontainerd: container c9f35af1836bf856001ca6156663f713c1217a697e8d2451927c67797fb5a770 restart canceled"
dockerd[1344]: time="2016-11-24T17:49:02.627116016+01:00" level=info msg="No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : [nameserver 8.8.8.8 nameserver 8.8.4.4]"
dockerd[1344]: time="2016-11-24T17:49:02.627152661+01:00" level=info msg="IPv6 enabled; Adding default IPv6 external servers : [nameserver 2001:4860:4860::8888 nameserver 2001:4860:4860::8844]"
dockerd[1344]: time="2016-11-24T18:19:51.472701647+01:00" level=warning msg="libcontainerd: container c9f35af1836bf856001ca6156663f713c1217a697e8d2451927c67797fb5a770 restart canceled"
dockerd[1344]: time="2016-11-24T18:19:56.712126199+01:00" level=info msg="No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : [nameserver 8.8.8.8 nameserver 8.8.4.4]"
dockerd[1344]: time="2016-11-24T18:19:56.712159759+01:00" level=info msg="IPv6 enabled; Adding default IPv6 external servers : [nameserver 2001:4860:4860::8888 nameserver 2001:4860:4860::8844]"
dockerd[1344]: time="2016-11-24T18:34:24.301786606+01:00" level=info msg="No non-localhost DNS nameservers are left in resolv.conf. Using default external servers : [nameserver 8.8.8.8 nameserver 8.8.4.4]"
dockerd[1344]: time="2016-11-24T18:34:24.302208751+01:00" level=info msg="IPv6 enabled; Adding default IPv6 external servers : [nameserver 2001:4860:4860::8888 nameserver 2001:4860:4860::8844]"

Answer 1

That Docker commands hanging bug happened after I deleted a container.

The daemon dockerd was in an abnormal state: it couldn't be started (sudo service docker start) after having been stopped (service docker stop).

# sudo service docker start
Redirecting to /bin/systemctl start docker.service
Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

# journalctl -xe
kernel: device-mapper: ioctl: unable to remove open device docker-253:0-19468577-d6f74dd67f106d6bfa483df4ee534dd9545dc8ca
...
systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
systemd[1]: Failed to start Docker Application Container Engine.
systemd[1]: Unit docker.service entered failed state.
systemd[1]: docker.service failed.
polkitd[896]: Unregistered Authentication Agent for unix-process:22551:34177094 (system bus name :1.290, object path /org
ESCESC
kernel: dev_remove: 41 callbacks suppressed
kernel: device-mapper: ioctl: unable to remove open device docker-253:0-19468577-fc63401af903e22d05a4518e02504527f0d7883f9d997d7d97fdfe72ba789863
...
dockerd[22566]: time="2016-11-28T10:18:09.840268573+01:00" level=fatal msg="Error starting daemon: timeout"
systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
systemd[1]: Failed to start Docker Application Container Engine.

Moreover, many zombie Docker processes could be observed using ps -eax | grep docker (presence of a "Z" in the "STAT" column), for example docker-proxies.

After rebooting the server and restarting Docker, the zombie processes disappeared and Docker commands were working again.

Answer 2

I just had a similar issue as well. Rebooting the server did not work for me. I got this issue, because I just installed a new container with some kind of errors. After that, most Docker commands did not respond. I fixed it by executing the following command:

docker system prune -a

This removes all unused containers. In my case also the container I just added. More information:

https://docs.docker.com/engine/reference/commandline/system_prune/