Can runc take its configuration on stdin?

[stuartpb]

It would be nice if there is a way to run runc with a configuration specified via stdin (for those of us with systems that build their container commands on the fly, although we'd prefer command-line overrides). If you're set on using runc to parse config.json in the working directory, then I'd settle for runc - to read the configuration from stdin.

[wking]

On Fri, Aug 14, 2015 at 09:49:08AM -0700, Stuart P. Bentley wrote:

It would be nice if there is a way to run runc with a
configuration specified via stdin (for those of us with systems that
build their container commands on the fly, although we'd prefer
command-line overrides). If you're set on using runc to parse
config.json in the working directory, then I'd settle for runc -
to read the configuration from stdin.

I expected /dev/stdin to work here, but for some reason it doesn't:

runc /dev/stdin <config.json

FATA[0000] Container start failed: inappropriate ioctl for device

That's with a build of v0.0.3 anyway.

[laijs]

@wking using /dev/stdin actually works, and it works well.

# runc /dev/stdin <config.json
FATA[0000] Container start failed: inappropriate ioctl for device

The failure reason is that the container needs the terminal, but the /dev/stdin in not the terminal in this usage.
After the config.json is changed ("terminal": false,), the command runc /dev/stdin <config.json works excellent.

So @stuartpb can disable the terminal of the container and use the way as @wking suggested

[wking]

On Tue, Aug 18, 2015 at 07:22:55PM -0700, Lai Jiangshan wrote:

The failure reason is that the container needs the terminal, but the
/dev/stdin in not the terminal.

Ah, thanks for clearing me up. I should have straced it ;), but we
might want to catch this and return a more specific error in this
case.

[laijs]

Yep, the runc should check the fd/0 fd/1 fd/2 before running the container if terminal==true
I add this to my todo list

[crosbymichael]

@stuartpb i don't know if this would be a good idea to pass configs via stdin because runc will use it's current STDIO as the containers IO. So if we pass the config via STDIN you couldn't do things like cat hello | runc

to cat something into the container's process.

[wking]

On Fri, Aug 21, 2015 at 11:36:51AM -0700, Michael Crosby wrote:

i don't know if this would be a good idea to pass configs via stdin
because runc will use it's current STDIO as the containers IO.

You currently use ‘runc config.json’ if you want to explicitly specify
your config path. With #210 that will become ‘runc start
config.json’, and @duglin 1 and I 2 both hope to see ‘runc
--config config.json COMMAND’ at some point.

But that doesn't mean that you shouldn't be able to use stdin for that
purpose if it's more convenient for you (e.g. your shell doesn't
support process substitution and you don't care about consuming the
container's stdin before the application is launched).

[tv42]

So use an fd that isn't stdin!

$ echo foo >bar
$ sh -x -c 'cat $0' /dev/fd/6 6<bar
+ cat /dev/fd/6
foo
$ 

[crosbymichael]

I think we can close this one now. In the latest spec updates we have more than one configuration and we want that to be more immutable so accepting something on stdin does not help this. Like my previous comment since we dup the runc stdio this will cause issues for other use cases.