Android - ADB backup is not working

Is ADB hung or just inconsiderate in reporting on what it's doing?

I came here with a similar question; on Win7 adb backup -apk -shared -all -nosystem -f path\to\backup_file.ab the Nexus 5 reported "com.stuff.foo .com.stuff.bar" ... for awhile and then stopped for a very long time, 20+ minutes, on "shared storage". Jacking up the confusion and anxiety level, after I picked up the phone when the screen blanked, the display auto-rotated, and then from that point didn't show any status messages at all.

On the PC side, the console never reported anything other than the initial unlock device message.

What kept me hanging in was that the backup_file.ab was created, the time-stamp continued to match current time within a minute or so, and the file size was multi-GB and kept increasing slowly -- albeit in fits and starts -- one pause was about 10 minutes(!), and then jumped by 0.5GB in a single shot.

After more than an hour the phone the Backup/Encryption Password screen closed of it's own accord, and the PC console prompt became active again. Neither one exited with a message to indicate whether they'd finished successfully or in an error state.

Final .ab file is just under 8GB. Nexus > Settings > Storage reports 12.55GB total space and 500mb free.

I think perhaps you just didn't wait long enough (understandable given the lack of feedback!) and that perhaps Linux spawns adb as a background process? (thus the return to prompt).