I met a problem while using docker.
Now I have a ubuntu based docker container. And in the container ,the user id is root by default which is not my expectation, I suppose the user id is like `abc` which is another user account on the HOST OS running docker.
I have tried the following ways but all fail:

```
su abc;

```

Then running `docker run xxx` to bring up a container, but login the container, the user in container is still `root`.

Then by adding the `-u` flag for docker run: like : 

```
docker run -t -i -u abc ubuntu /bin/bash

```

the the docker show errors `unable to find user abc`

Can some one tell me how to fix it?

Or does docker support run a container in which the user is a specific one than the default `root`?