MySQL: Cannot connect to Server via SSH. 'reading initial communication packet', system error: 0

Question

I am running Debian 8.2 and the install is quite fresh. I try to connect to my MySQL server via SSH using Sequel Pro. I always get this error:

Lost connection to MySQL server at 'reading initial communication packet', system error: 0

When I run

mysql -u root -p

on the server, everything works perfectly. But not from remote.

At first I thought it might be iptables, so I (temporarily) disabled all rules. iptables -L now returns:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Then I checked my.cnf, but all the parameters I could think of look correct:

[client]
port            = 3306
socket          = /var/run/mysqld/mysqld.sock

[mysqld_safe]
socket          = /var/run/mysqld/mysqld.sock
nice            = 0

[mysqld]
user            = mysql
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
port            = 3306
basedir         = /usr
datadir         = /var/lib/mysql
tmpdir          = /tmp
lc-messages-dir = /usr/share/mysql
skip-external-locking

bind-address            = 127.0.0.1

The output of my mysql log files also looks ok

150609 17:15:07 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
150609 17:15:07 [Warning] Using unique option prefix key_buffer instead of key_buffer_size is deprecated and will be removed in a future release. Please use the full name instead.
150609 17:15:07 [Note] /usr/sbin/mysqld (mysqld 5.5.43-0+deb8u1) starting as process 18347 ...
150609 17:15:07 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead.
150609 17:15:07 [Note] Plugin 'FEDERATED' is disabled.
150609 17:15:07 InnoDB: The InnoDB memory heap is disabled
150609 17:15:07 InnoDB: Mutexes and rw_locks use GCC atomic builtins
150609 17:15:07 InnoDB: Compressed tables use zlib 1.2.8
150609 17:15:07 InnoDB: Using Linux native AIO
150609 17:15:07 InnoDB: Initializing buffer pool, size = 128.0M
150609 17:15:07 InnoDB: Completed initialization of buffer pool
150609 17:15:07 InnoDB: highest supported file format is Barracuda.
150609 17:15:07 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
150609 17:15:08  InnoDB: Waiting for the background threads to start
150609 17:15:09 InnoDB: 5.5.43 started; log sequence number 1654586
150609 17:15:09 [Note] Server hostname (bind-address): '127.0.0.1'; port: 3306
150609 17:15:09 [Note]   - '127.0.0.1' resolves to '127.0.0.1';
150609 17:15:09 [Note] Server socket created on IP: '127.0.0.1'.
150609 17:15:09 [Note] Event Scheduler: Loaded 0 events
150609 17:15:09 [Note] /usr/sbin/mysqld: ready for connections.

And I cannot find any problems with my Clients configuration:

MySQL Host: 127.0.0.1
User: root
Password: ***
Port: 3306
SSH Host: mydomain.com
SSH User: sshuser
SSH Key: sshkey

I also don't have anything in /etc/hosts.allow and /etc/hosts.deny

Note that SSH connects successfully but MySQL fails.

I am lost. Can anybody help?

Answer 1

Well, if anybody should ever encounter the same problem:

Note to self: When setting up SSH, you MUST set the following option in /etc/ssh/sshd_config:

AllowTcpForwarding yes

If you don't, then your packets will be silently dropped at the server. This results in the above error message.

Credit goes to achbed