Sshd: Service exited with abnormal code: 255

ssh

Every SSH connection exits with an abnormal code.

For example

ssh corti@myhost.example.com true

results in

Feb 11 10:16:47 mac-mini com.apple.xpc.launchd[1]: (com.openssh.sshd.163F2BE0-40C6-4B17-AB4E-5A0A07A524DE): Service instances do not support events yet.
Feb 11 10:16:48 mac-mini.home sshd[35674]: Accepted publickey for corti from ***.***.***.*** port 65030 ssh2
Feb 11 10:16:48 mac-mini.home sshd[35676]: Received disconnect from ***.***.***.***: 11: disconnected by user
Feb 11 10:16:48 mac-mini com.apple.xpc.launchd[1]: (com.openssh.sshd.163F2BE0-40C6-4B17-AB4E-5A0A07A524DE[35674]): Service exited with abnormal code: 255

Why is sshd exiting with a non zero return value (i.e., 225)?

Best Answer

In recent macOS versions, the rotten fruit geniuses have restricted SSH access to admin users only. I was having this 'service exited with abnormal code' issue and I fixed it by Preferences -> Sharing -> Remote Login: On and 'Allow Access to': All Users (or the users/groups you want). You must be an admin to do that (you must be able to unlock the locker icon on the bottom left).

Two hours wasted, damn idiots...

Related Solutions

MacOS – Logging for SSHD when started from Launchd with `-d` option

To add the -d argument to sshd, it should be added as a new element to the array:

<string>-d</string>

The section should look like:

<key>ProgramArguments</key>
    <array>
        <string>-i</string>
        <string>-d</string>
    </array>

Instead of editing the plist files directly, you can use /usr/libexec/PlistBuddy (-h to show help).

There is a utility script ssh-util.rb that can turn logging on/off. It is part of the OpenSSH-189 package found at: opensource.apple.com.

Link to ssh-util.rb

Here are the required commands to run (as produced from the ruby script):

/usr/bin/ruby ./ssh-util.rb -l on -v --debug --dryrun

or manually:

sudo /usr/libexec/PlistBuddy -c "add :ProgramArguments:2 string '-ddd'" /System/Library/LaunchDaemons/ssh.plist
sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist
sudo launchctl load /System/Library/LaunchDaemons/ssh.plist
sudo touch /var/run/com.openssh.sshd-asl-enabled

When finished debugging,, you'll need to run either:

/usr/bin/ruby ./ssh-util.rb -l off -v --debug --dryrun

or manually:

sudo /usr/libexec/PlistBuddy -c "Delete :ProgramArguments:2" /System/Library/LaunchDaemons/ssh.plist
sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist
sudo launchctl load /System/Library/LaunchDaemons/ssh.plist
sudo rm -f /var/run/com.openssh.sshd-asl-enabled

Notes on OS X Logging

Network SSH Issue – SSHD Regular Exit Code 255

That's the log entry performed when sshd denies a connection. You're probably seeing unauthorised users trying to brute force their way in by trying common usernames and passwords. There used to also be a log entry directly from sshd itself telling you the IP address and username attempted, but Apple has decided to labotomize standard UNIX logging from sshd.