Issue: Error while running ubuntu bash shell in docker - bash

Question

I am running docker on my arm based 32 bit device.
However, when i try to run an ubuntu bash shell as a docker container via the command : docker run -it ubuntu bash , I keep getting the following error:
docker: Error response from daemon: OCI runtime create failed:
container_linux.go:348: starting container process caused
"process_linux.go:402: container init caused \"open /dev/ptmx: no such file or directory\"": unknown.
Here's what docker info gives:
Containers: 4
Running: 0
Paused: 0
Stopped: 4
Images: 3
Server Version: 18.06.1-ce
Storage Driver: vfs
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
seccomp
Profile: default
Kernel Version: 3.10.65-00273-gfa38327-dirty
OSType: linux
Architecture: armv7l
CPUs: 4
Total Memory: 923MiB
ID: 2PDV:3KHU:VZZM:DM6F:4MVR:TXBN:35YJ:VWP5:TMHD:GMKW:TPMI:MALC
Docker Root Dir: /opt/usr/media/docker_workdir
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: false
It would be great if someone could tell me what's wrong and how can I fix this ?

Answer 1

It could be that, for one reason or another, your docker container can't find its own /dev/ptmx or even perhaps your /dev/ altogether.
One quick solution is to do:
docker run -it -v /dev:/dev ubuntu bash
This binds your /dev/ directory to the container's, meaning that they will use the same files.
Notice that, although in of itself this operation is harmless, in production environments this means that the isolation between the host's and the container's devices is gone.
For that reason, make sure to only ever use this trick in test environments.

Answer 2

It looks like your OS is missing pseudo-terminals (PTY) - a device that has the functions of a physical terminal without actually being one.
The file /dev/ptmx is a character file with major number 5
and minor number 2, usually of mode 0666 and owner.group
of root.root. It is used to create a pseudo-terminal mas­ter and slave pair.
FILES
/dev/ptmx - UNIX 98 master clone device
/dev/pts/* - UNIX 98 slave devices
/dev/pty[p-za-e][0-9a-f] - BSD master devices
/dev/tty[p-za-e][0-9a-f] - BSD slave devices
Reference: http://man7.org/linux/man-pages/man7/pty.7.html
This is by default included into Linux kernel. Maybe lack of it is somehow related to your OS architecture. Also, I'm not sure how can you fix, maybe try to update && upgrade OS.
Quick workaround if you don't need a tty would be to skip -t flag:
docker run -i ubuntu bash
In docker run -it, -i/--interactive means "keep stdin open" and -t/--tty means "tell the container that stdin is a pseudo tty". The key here is the word "interactive". If you omit the flag, the container still executes /bin/bash but exits immediately. With the flag, the container executes /bin/bash then patiently waits for your input. That means now you will have bash session inside the container, so you can ls, mkdir, or do any bash command inside the container.

Answer 3

one workable fix:
docker exec -i hello-world rm /dev/ptmx
docker exec -i hello-world mknod /dev/ptmx c 5 2
or enable kernel config: CONFIG_DEVPTS_MULTIPLE_INSTANCES=y