unable to connect to beta: unable to connect to endpoint: unable to dial agent endpoint: unable to handshake with agent process: server magic number incorrect

[OliverRC]

I restarted my MacBook and for some reason warden will no longer start due to a mutagen error.

Details:

• MacOS 15.4 (but also happenedd on 15.3)
• warden v0.15.0
• mutagen v0.18.0

Error:

warden env start

[+] Running 8/8
 ✔ Container darhos-rabbitmq-1    Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-opensearch-1  Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-db-1          Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-redis-1       Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-php-fpm-1     Started                                                                                                                                                                                                                                                                                             0.2s 
 ✔ Container darhos-php-debug-1   Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-nginx-1       Started                                                                                                                                                                                                                                                                                             0.1s 
 ✔ Container darhos-varnish-1     Started                                                                                                                                                                                                                                                                                             0.1s 
Connecting to agent (POSIX)...                                                  
Error: unable to connect to beta: unable to connect to endpoint: unable to dial agent endpoint: unable to handshake with agent process: server magic number incorrect
ERROR: Command `mutagen sync create -c "${MUTAGEN_SYNC_FILE}" --label "warden-sync=${WARDEN_ENV_NAME}" --ignore "${WARDEN_SYNC_IGNORE:-}" "${WARDEN_ENV_PATH}${WARDEN_WEB_ROOT:-}" "docker://$($WARDEN_BIN env ps -q php-fpm)/var/www/html"` at /opt/homebrew/Cellar/warden/0.15.0/commands/sync.cmd:53 failed with exit code 1

I didn't change anything and now it's breaking. I've searched trying to resolve this but coming up dry so I come cap in hand hoping someone can assist.

[stasadev]

mutagen v0.18.0

Try the latest mutagen v0.18.1

[OliverRC]

Shot! I did the upgrade and it resolved the issue. Here is what I did

brew upgrade mutagen

Then I needed to manually restart the daemon otherwise I was getting the error Error: unable to connect to daemon: client/daemon version mismatch (daemon restart recommended)

mutagen daemon stop
mutagen daemon start

[maphilipps]

I'm experiencing the exact same "server magic number incorrect" error on macOS with DDEV, confirming this is still an active issue even with the latest versions.

System Configuration:

macOS: ARM64 (Apple Silicon)
DDEV Version: v1.24.6 (latest stable)
Mutagen: 0.18.0 (provided by DDEV)
Docker Providers: Issue occurs with both OrbStack and Docker Desktop
Architecture: arm64

Error Details:

Error: unable to connect to beta: unable to connect to endpoint: unable to dial agent endpoint: unable to handshake with agent process: server magic number incorrect
Troubleshooting Attempts (all failed):

• ddev mutagen reset multiple times
• Complete Mutagen cleanup (rm -rf ~/.mutagen, daemon stop/start)
• Removed conflicting Mutagen installations from /usr/local/bin/mutagen
• Docker provider switching (OrbStack ↔ Docker Desktop)
• Complete Docker image cleanup and rebuild
• DDEV project reinitialization
• Different project paths (to avoid label length issues)

Key Observations:

• Issue is system-wide - affects all DDEV projects
• Occurs with both major Docker providers on macOS
• Persistent across DDEV updates (issue exists even with v1.24.6 which supposedly fixed Docker 28 compatibility)
• Reproducible - happens on every ddev start attempt

Current Workaround:

The only reliable solution is disabling Mutagen entirely:

ddev mutagen reset && ddev config global --performance-mode=none && ddev config --performance-mode=none

This appears to be a fundamental protocol handshake issue between Mutagen host daemon and container agents on certain macOS ARM64 configurations. The error suggests the magic number (protocol identifier) exchange is failing during agent connection establishment.

[rfay]

@maphilipps please upgrade to current DDEV v1.24.6, thanks.

Please bring the discussion over to DDEV. We've been using mutagen v0.18.1 for quite some time, since this problem appeared in April, 2025.

You may need to look at the FAQ, https://ddev.readthedocs.io/en/stable/users/usage/faq/#why-do-i-have-an-old-ddev

[rfay]

If you show ddev version and the file output from ddev debug test it will help us to understand. I think you probably have more than one ddev binary installed. which -a ddev will show you that.

[NekiMedo]

Having the same issue (during sync create command) between two Ubuntu 22.04.4 LTS boxes

Error: unable to connect to beta: unable to connect to endpoint: unable to dial agent endpoint: unable to handshake with agent process: unable to receive server magic number: EOF (error output: Connection timed out during banner exchange\r
Connection to UNKNOWN port 65535 timed out)

It started happening when our IT people imposed a policy of using ssh passwords on top of public key authentication.
Mutagen version 0.18.1

[rfay]

This issue is about "server magic number incorrect", you have a different problem "unable to receive server magic number", and it sounds like you're quite sure it's a configuration error.