On the emulator, I can unmount the SD card from the Settings.
I can then mount it on my OS, then unmount it normally.
I haven\'t been able to figure out how
The developers guide suggests that this isn't possible:
SD Card Emulation
You can create a disk image and then load it to the emulator at startup, to simulate the presence of a user's SD card in the device. To do this, you can use the android tool to create a new SD card image with a new AVD, or you can use the mksdcard utility included in the SDK.
The sections below describe how to create an SD card disk image, how to copy files to it, and how to load it in the emulator at startup.
Note that you can only load disk image at emulator startup. Similarly, you can not remove a simulated SD card from a running emulator. However, you can browse, send files to, and copy/remove files from a simulated SD card either with adb or the emulator.
The emulator supports emulated SDHC cards, so you can create an SD card image of any size up to 128 gigabytes.
While Android will unmount the SD card, the emulator process keeps the backing file open.
$ ls -go /proc/`pidof emulator`/fd | grep sdcard.img
lrwx------ 1 64 2010-05-13 01:50 10 -> /home/x/.android/avd/WithSD.avd/sdcard.img
Someone more familiar with QEMU may be able to provide further insight but, if I were you, I would just try to use NFS to solve this problem.
I tried going to Settings and unmounting the SD card and this worked fine. Give it a try; remounting it is quite simple.
Doesn't seem like this can be done via adb/cli though.