October 11, 2019 at 10:53 AM by Dr. Drang
A few days ago, I ran into an odd and very old bug that isn’t even Apple’s fault. Imagine that!
My discovery did start with a Apple bug, though. I was working on my larger iPad Pro and saved a couple of email attachments to a new folder in iCloud Drive. At least, that’s what I thought I’d done. When I opened Files on my smaller iPad a few minutes later, neither the files nor their enclosing folder, which I had created on the spot while saving the files, were visible. Probably just a brief delay in syncing, I thought, but I was wrong. When I looked again half an hour later, nothing had synced. I could see the new files and folder on the large iPad but not the small one.
I wondered if the files had synced to my Macs. So I opened up Transmit on one of the iPads and tried to SFTP into my home iMac to look for the files. Couldn’t connect. Tried to SFTP into my office iMac and couldn’t connect there, either. I wondered if maybe iOS 13 was finally the end of Transmit for iOS, but a quick test showed I was able to connect to the server that hosts this blog. Also, I was able to use Prompt to log into both iMacs via SSH, so it was clear that their SSH server daemons were up and running.
Several unfruitful Googlings later, I sat down at my home iMac and tried to diagnose the problem. When I entered
into Terminal, I got this response
Received message too long 1113682792 Ensure the remote shell produces no output for non-interactive sessions.
I didn’t understand how the remote shell could be set up to produce no output—shells are supposed to produce output, aren’t they?—but I figured this sort of raw, system-level error message would be a better search term than the Transmit error messages, which were written by Panic.
sftp and/or scp may fail at connection time if you have shell initialization (.profile, .bashrc, .cshrc, etc) which produces output for non-interactive sessions. This output confuses the sftp/scp client.
So the problem is not that the shell produces output, it’s that it produces output upon initialization. And I knew immediately why my shells were doing that.
A month or so ago, I was messing around different shells and different versions of shells, and to keep track of what was running, I had added these lines this to the top of
echo "Loading .bashrc..." echo $BASH_VERSION
These were the culprits. They were fine in an interactive SSH session, but were triggering a long-standing bug in an SFTP session. I commented out the lines and could make SFTP connections via Transmit (and ShellFish and FileBrowser) to both iMacs again.
The OpenSSH people don’t seem to think of this as a bug. The Stack Exchange answer says it’s been around at least ten years, and the FAQ says the fix is “you need to modify your shell initialization.”
In other words, “you’re initializing it wrong.”
By the way, once I got this SFTP stuff straightened out, I learned that the new files and folder (remember those? this is a song about Alice) weren’t on either of my Macs, so some combination of Files and iCloud Drive had screwed up. While still on my Mac, I created a new folder and saved the email attachments into it. They appeared in Files on both iPads immediately, except that the new folder was called
untitled folder on the larger iPad.
I hope it takes Apple less than ten years to recognize and clean up these iCloud/Files bugs.