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What does 'DPY-6005: cannot connect to database. Connection failed with "[Errno 61] Connection refused"' mean with python-oracledb

On macOS with Python 3.9.6 the Python code using Oracle's python-oracledb driver:
import oracledb
import os
un = os.environ.get("PYTHON_USERNAME")
pw = os.environ.get("PYTHON_PASSWORD")
cs = "localhost/orclpdb1"
c = oracledb.connect(user=un, password=pw, dsn=cs)
gives the error:
DPY-6005: cannot connect to database. Connection failed with "[Errno 61] Connection refused"
on Linux the error is like:
DPY-6005: cannot connect to database. Connection failed with "[Errno 111] Connection refused"
What do these mean?
[Update: in python-oracledb 1.0.1 the error is wrapped with DPY-6005. In 1.0.0 just the lower level Python part of the error was shown.]

One scenario is that the database port you used (or the default port 1521) is
not correct. Find the correct port and use that instead. For example if your
database listener is listening on port 1530 instead of the default port 1521, then you could try the connection string:
cs = "localhost:1530/orclpdb1"
Make sure the hostname is correct: you may have connected to the wrong machine.

In my experience, "connection refused" often means that the connection was actively denied, which could mean that the database is protected by a firewall. If you have already confirmed the hostname and port are correct and are still getting this error then determine if there is a firewall, either on the database server itself or elsewhere on the network, and have a rule created to allow access or disable it entirely (assuming it is safe to do so).

Connecting to Teradata using teradatasql module in Python

I am trying to connect to Teradata using teradatasql module in Python. The code is running fine on localhost, but once deployed on the server as part of the server code, it is throwing the error.
the code:
import teradatasql
try:
host, username, password = 'hostname', 'username', '****'
session = teradatasql.connect(host=host, user=username, password=password, logmech="LDAP")
except Exception as e:
print(e)
Error I am getting on server:
[Version 16.20.0.60] [Session 0] [Teradata SQL Driver] Failure receiving Config Response message header↵ at gosqldriver/teradatasql.
(*teradataConnection).makeDriverError TeradataConnection.go:1101↵ at gosqldriver/teradatasql.
(*teradataConnection).sendAndReceive TeradataConnection.go:1397↵ at gosqldriver/teradatasql.newTeradataConnection TeradataConnection.go:180↵ at gosqldriver/teradatasql.(*teradataDriver).
Open TeradataDriver.go:32↵ at database/sql.dsnConnector.Connect sql.go:600↵ at database/sql.(*DB).conn sql.go:1103↵ at database/sql.
(*DB).Conn sql.go:1619↵ at main.goCreateConnection goside.go:275↵ at main.
_cgoexpwrap_212fad278f55_goCreateConnection _cgo_gotypes.go:240↵ at runtime.call64 asm_amd64.s:574↵ at runtime.cgocallbackg1 cgocall.go:316↵ at runtime.cgocallbackg cgocall.go:194↵ at runtime.cgocallback_gofunc asm_amd64.s:826↵ at runtime.goexit asm_amd64.s:2361↵Caused by read tcp IP:PORT->IP:PORT: wsarecv: An existing connection was forcibly closed by the remote host

The root cause of this error is outlined here by tomnolan:
The stack trace indicates that a TCP socket connection was made to the database, then the driver transmitted a Config Request message to the database, then the driver timed out waiting for a Config Response message from the database.
In other words, the driver thought that it had established a TCP socket connection, but the TCP socket connection was probably not fully successful, because a failure occurred on the initial message handshake between the driver and the database.
The most likely cause is that some kind of networking problem prevented the driver from properly connecting to the database.
I had this issue today and resolved it by altering my host. I am also on a VPN and found that the actual host name in DNS didn't work, but the ALIAS available did. For example on Windows:
C:\WINDOWS\system32>nslookup MYDB-TEST # <-- works
Server: abcd.domain.com
Address: <OMITTED>
Name: MYDB.domain.com # <-- doesn't work
Address: <OMITTED>
Aliases: mydb-test.domain.com # <-- works
I recognize this may be a specific solution option that may not work for everyone, but the root of the problem is confirmed to be a TCP connection issue from my experience.

How to setup ssh tunnel dynamically in python?

I am trying to build a tunnel to then connect to an Oracle DB, but tunnel cannot be opened. Error is the following:
ERROR | Problem setting SSH Forwarder up: Couldn't open tunnel localhost:1521 <> XXXXXXXXX:1521 might be in use or destination not reachable.
sshtunnel.HandlerSSHTunnelForwarderError: An error occurred while opening tunnels.
My code is set as:
self.tunnel = sshtunnel.SSHTunnelForwarder((conn_data['gateway'], int(conn_data['gateway_port'])),
ssh_username=conn_data['username'],
ssh_password=password,
remote_bind_address=(conn_data['remote_bind'],
int(conn_data['remote_port'])),
local_bind_address=(conn_data['local_bind'],
int(conn_data['local_port'])))
The code works fine if I am inside the network of the company I work for. But if I am connected through VPN, I get the above error. My guess is that the VPN is built over the same tunnel.
I tried changing the local_port and removing the local bind, but if I do that, I get the error:
cx_Oracle.DatabaseError: ORA-12541: TNS:no listener
So, how can I dynamically set the port of SSHTunnelForwarder so it can access my DB through my already set VPN?
Note: changing the VPN's configuration or not using it is not an option.

Problem solved. The issue was that my VPN was using the same port as me (which caused the first error), and my Oracle connection was pointing to this port also (what caused error ORA-12541).
To solve it, I had to change conn_data['local_port'] to another port and set the port of my oracle connection to this same port:
self.tunnel = sshtunnel.SSHTunnelForwarder((conn_data['gateway'],
int(conn_data['gateway_port'])),
ssh_username=conn_data['username'],
ssh_password=password,
remote_bind_address=(conn_data['remote_bind'], int(conn_data['remote_port'])),
local_bind_address=(conn_data['local_bind'], 1234))
self.connection.connect(conn_data['host'],
port=1234,
username=conn_data['username'],
password=password,
look_for_keys=False)

How do I configure PyMySQL connect for SSL?

I'm trying to connect my database using SSL with PyMySQL, but I can't find good documentation on what the syntax is.
These credentials work in Workbench and with the CLI, but I get this error when using PyMySQL.
Can't connect to MySQL server on 'server.domain.com' ([WinError 10061] No connection could be made because the target machine actively refused it)")
db_conn = pymysql.connect(
host=db_creds['host'],
user=db_creds['user'],
passwd=db_creds['passwd'],
db=db_creds['db'],
charset=db_creds['charset'],
ssl={'ssl':{'ca': 'C:/SSL_CERTS/ca-cert.pem',
'key' : 'C:/SSL_CERTS/client-key.pem',
'cert' : 'C:/SSL_CERTS/client-cert.pem'
}
}
)
If I shut SSL off and drop the SSL parameter, I can connect unsecured just fine. What am I doing wrong with the SSL parameter?
Edit: PyMySQL now wants ssl parameters listed like this instead of in a dict.
db_conn = pymysql.connect(
host=db_creds['host'],
user=db_creds['user'],
passwd=db_creds['passwd'],
db=db_creds['db'],
charset=db_creds['charset'],
ssl_ca='C:/SSL_CERTS/ca-cert.pem',
ssl_key='C:/SSL_CERTS/client-key.pem',
ssl_cert='C:/SSL_CERTS/client-cert.pem'
)

Thanks for the help everyone. The syntax listed in the question is right, but the server I was attempting a connection to was using a non-standard port. I needed to add
port = db_creds['port']
Thanks, MannyKary, for the clue.

I had the same problem connecting pyMysql using client-side cert and key for users that REQUIRE X509, the TiDB (mySQL 5.7 compatible) server complained that no cert was supplied!!!
[2021/05/18 16:31:23.881 +00:00] [INFO] [privileges.go:258] ["ssl check failure, require x509 but no verified cert"] [user=mindline_root] [host=%]
Looking through the sourcecode of PyMysql 1.0.2, it appears that the ssl parameter is now a boolean instead of a ssl_dict, so you should put all your ssl parameters into individual arguements, e.g.,
db_conn = pymysql.connect(
host=db_creds['host'],
user=db_creds['user'],
passwd=db_creds['passwd'],
db=db_creds['db'],
charset=db_creds['charset'],
ssl_ca='C:/SSL_CERTS/ca-cert.pem',
ssl_key='C:/SSL_CERTS/client-key.pem',
ssl_cert='C:/SSL_CERTS/client-cert.pem'
)

MySQL error: 2013, "Lost connection to MySQL server at 'reading initial communication packet', system error: 0"

I'm having an issue connecting to my local MySQL database using Python's MySQLdb library. The script has been working well previously, but I will occasionally get the MySQL error in the title. There seems to be no explanation for when the error occurs, and the script is always run from the same machine with the same arguments.
The MySQL server is running as a service on Windows XP SP3 using port 3306 (locally hosted phpMyAdmin works), and the script is run from an Ubuntu 10.04 guest operating system in Oracle VM VirtualBox.
I am currently working around this issue by opening a command prompt and executing 'net stop MySQL' then 'net start MySQL'. This allows me to run the script a few times again before resulting in the error, which I've been fixing by restarting the MySQL service.
As I am still making changes to the script, there are occasions when the script raises an exception and doesn't exit gracefully, though I do catch the exception and close the cursor and connection.
The code to connect to the database:
def __init__(self):
try:
print "Connecting to the MySQL database..."
self.conn = MySQLdb.connect( host = "192.168.56.1",
user = "guestos",
passwd = "guestpw",
db = "testdb")
self.cursor = self.conn.cursor(MySQLdb.cursors.DictCursor)
print "MySQL Connection OK"
except MySQLdb.Error, e:
print "MySQLdb error %d: %s" % (e.args[0],e.args[1])
raise
The full error generated when this happens is as follows:
MySQLdb error 2013: Lost connection to MySQL server at 'reading initial communication packet', system error: 0
Traceback (most recent call last):
File "search.py", line 45, in <module>
dataHandler = DataHandler()
File "/home/guestos_user/workspace/Search/src/data_handler.py", line 25, in __init__
db = "testdb")
File "/usr/lib/pymodules/python2.6/MySQLdb/__init__.py", line 81, in Connect
return Connection(*args, **kwargs)
File "/usr/lib/pymodules/python2.6/MySQLdb/connections.py", line 170, in __init__
super(Connection, self).__init__(*args, **kwargs2)
_mysql_exceptions.OperationalError: (2013, "Lost connection to MySQL server at 'reading initial communication packet', system error: 0")

sudo vi /etc/mysql/my.cnf
delete
bind-address = 127.0.0.1
then
sudo reboot now
That's it. Be aware that this will make your mysql server less secure as you are exposing it.

I have seen this happen when child processes try to share the same mysql connection id (solution = create new connections for each child process). I'm not sure if this is also possible when sharing connection objects with multiple threads.
However, that's only one of the many possible causes. See VVS's answer in MySQL Error 2013 for a list of troubleshooting resources.

Do you have in your MySQL server an acount called guestos#YOURIPADDRESS?
You must have an account to access to your MySQL server from YOURIPADDRESS!
For example:
Your IP address is 192.168.56.2; then you must create and account if not exist to access.
mysql> create user guestos#192.168.56.2 identified by 'guestpw';

The problem fixed for me just by restarting my mac. Though there might be a more specific fix for it.

I received a similar error when attempting to connect to my MySQL server remotely through a user with the sufficient permissions.
After editing the /etc/mysql/my.cnf file to include
[mysqld]
bind-address=xx.xx.xxx.xxx
where xx.xx.xxx.xxx is my local IP address, I began experiencing the exact same error as you. From there, I found an answer regarding this issue (answered by Coffee Converter) which worked for me, and can be found here: Lost connection to MySQL server at 'reading initial communication packet', system error: 0 on a windows machine
All I did to fix the issue for myself was edit the /etc/hosts.allow to include
mysqld: ALL: allow
Works great now! I hope this helped :)

Could you change the bind-address=localhost and restart MySQL server? Seems like this issue is related to yours: http://forums.mysql.com/read.php?152,355740,355742#msg-355742
Also this-
If MySQL port is wrong result is MySQL client error 2013 "Lost
connection ...". Note that this error also occurs if port forwarding
is disabled in SSH configuration (the configuration parameter
'AllowTcpForwarding' is set to 'no' in the 'sshd_config' file). It
(here) simply tells that there is no connection from SSH to MySQL for
some reason. But the mySQL client API 'thinks' there was one
connection and that is why is says 'Lost connection ...' and not
'Can’t connect...'. There was one successful connection - but not to
the MySQL server - to the SSH daemon only! But the MySQL client API is
not designed to 'see' the difference!
Refer this.

I run a windows server and from time to time the php-win.exe will load and stay in the processes list on the windows task manager.
If you know the host file is correct, then kill the php-win.exe process and restart iis iisreset
If you are running windows then your problem should be solved.

I've had the exact same mysql error (ERROR 2013 (HY000): Lost connection to MySQL server at 'reading initial communication packet', system error: 0=) and have resolved it by adding a newline to /etc/hosts.deny.

Possibility: your database is corrupted.
I encountered this situation when I was running an UPDATE statement on a specific row of a specific table. (Specifically, I was editing an item in a Django Admin site.) Most of the time the database worked just fine.
I finally resolved the problem by running:
OPTIMIZE TABLE `your_table`
After that everything was OK, no connection lost.
Conclusion:
The problem "Lost connection to MySQL server at 'reading initial communication packet'", sometimes "Can't connect to MySQL server on '127.0.0.1'", could possibly be resolved by running a full database optimization if the database is corrupted. For more info, read this.

Just to further extend the list of possible causes: it could also be as banal as wrong connection data/credentials. I encountered this error in conjunction with sqlalchemy:
sqlalchemy.exc.OperationalError: (mysql.connector.errors.OperationalError) 2013 (HY000): Lost connection to MySQL server at 'reading initial communication packet', system error: 0
In my code I connect to several different databases and once in a while it happens that I don't get the mapping between the db connections and their credentials (e.g. ip address of server, db-name, password etc.) right, which then also results in the 2013-error (in this case wrapped into an sqlalchemy operational error).

setting.py file set like:
'ENGINE': 'django.db.backends.mysql',
'NAME': 'test2',
'USER': 'root',
'PASSWORD': '',
'HOST': 'localhost',
'PORT': '3308',

This bug report might be of interest to you. Don't know if this will help you, but some were able to solve it by using the name of the server rather than the ip address in the connection properties.