# Linux Runtime

## File descriptors

By default, only the `stdin`, `stdout` and `stderr` file descriptors are kept open for the application by the runtime.
The runtime MAY pass additional file descriptors to the application to support features such as [socket activation](http://0pointer.de/blog/projects/socket-activated-containers.html).
Some of the file descriptors MAY be redirected to `/dev/null` even though they are open.

## Dev symbolic links

After the container has `/proc` mounted, the following standard symlinks MUST be setup within `/dev/` for the io.

|    Source       | Destination |
| --------------- | ----------- |
| /proc/self/fd   | /dev/fd     |
| /proc/self/fd/0 | /dev/stdin  |
| /proc/self/fd/1 | /dev/stdout |
| /proc/self/fd/2 | /dev/stderr |