Connecting from Linux or macOS

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This article discusses how you can create a connection to a SQL Server database.

Connection Properties

See DSN and Connection String Keywords and Attributes for all the connection string keywords and attributes supported on Linux and macOS.

Important

When connecting to a database that uses database mirroring (has a failover partner), do not specify the database name in the connection string. Instead, send a use database_name command to connect to the database before executing your queries.

The value passed to the Driver keyword can be one of the following:

  • The name you used when you installed the driver.

  • The path to the driver library, which was specified in the template .ini file used to install the driver.

DSNs are optional. You can use a DSN to define connection string keywords under a DSN name that you can then reference in the connection string. To create a DSN, create (if necessary) and edit the file ~/.odbc.ini (.odbc.ini in your home directory) for a User DSN only accessible to the current user, or /etc/odbc.ini for a System DSN (administrative privileges required.) The following odbc.ini is a sample that shows the minimal required entries for a DSN:

# [DSN name]
[MSSQLTest]  
Driver = ODBC Driver 18 for SQL Server  
# Server = [protocol:]server[,port]  
Server = tcp:localhost,1433
Encrypt = yes
#
# Note:  
# Port isn't a valid keyword in the odbc.ini file  
# for the Microsoft ODBC driver on Linux or macOS
#  

To connect using the above DSN in a connection string, you would specify the DSN keyword like: DSN=MSSQLTest;UID=my_username;PWD=my_password
The above connection string would be the equivalent of specifying a connection string without the DSN keyword like: Driver=ODBC Driver 18 for SQL Server;Server=tcp:localhost,1433;Encrypt=yes;UID=my_username;PWD=my_password

You can optionally specify the protocol and port to connect to the server. For example, Server=tcp:servername,12345. The only protocol supported by the Linux and macOS drivers is tcp.

To connect to a named instance on a static port, use Server=servername,port_number. Connecting to a dynamic port isn't supported before version 17.4.

Alternatively, you can add the DSN information to a template file, and execute the following command to add it to ~/.odbc.ini :

odbcinst -i -s -f <template_file>

For complete documentation on ini files and odbcinst, see the unixODBC documentation. For entries in the odbc.ini file specific to the ODBC Driver for SQL Server, see DSN and Connection String Keywords and Attributes for ones supported on Linux and macOS.

You can verify that your driver is working by using isql to test the connection, or you can use this command:

bcp master.INFORMATION_SCHEMA.TABLES out OutFile.dat -S <server> -U <name> -P <password>

Using TLS/SSL

You can use Transport Layer Security (TLS), previously known as Secure Sockets Layer (SSL), to encrypt connections to SQL Server. TLS protects SQL Server user names and passwords over the network. TLS also verifies the identity of the server to protect against man-in-the-middle (MITM) attacks.

Enabling encryption increases security at the expense of performance.

For more information, see Encrypting Connections to SQL Server and Using Encryption Without Validation.

Regardless of the settings for Encrypt and TrustServerCertificate, the server login credentials (user name and password) are always encrypted. The following tables show the effect of the Encrypt and TrustServerCertificate settings.

ODBC Driver 18 and newer

Encrypt Setting Trust Server Certificate Server Force Encryption Result
No No No Server certificate isn't checked.
Data sent between client and server isn't encrypted.
No Yes No Server certificate isn't checked.
Data sent between client and server isn't encrypted.
Yes No No Server certificate is checked.
Data sent between client and server is encrypted.
Yes Yes No Server certificate isn't checked.
Data sent between client and server is encrypted.
No No Yes Server certificate is checked.
Data sent between client and server is encrypted.
No Yes Yes Server certificate isn't checked.
Data sent between client and server is encrypted.
Yes No Yes Server certificate is checked.
Data sent between client and server is encrypted.
Yes Yes Yes Server certificate isn't checked.
Data sent between client and server is encrypted.
Strict - - TrustServerCertificate is ignored. Server certificate is checked.
Data sent between client and server is encrypted.

Note

Strict is only available against servers that support TDS 8.0 connections.

ODBC Driver 17 and older

Encrypt Setting Trust Server Certificate Server Force Encryption Result
No No No Server certificate isn't checked.
Data sent between client and server isn't encrypted.
No Yes No Server certificate isn't checked.
Data sent between client and server isn't encrypted.
Yes No No Server certificate is checked.
Data sent between client and server is encrypted.
Yes Yes No Server certificate isn't checked.
Data sent between client and server is encrypted.
No No Yes Server certificate isn't checked.
Data sent between client and server is encrypted.
No Yes Yes Server certificate isn't checked.
Data sent between client and server is encrypted.
Yes No Yes Server certificate is checked.
Data sent between client and server is encrypted.
Yes Yes Yes Server certificate isn't checked.
Data sent between client and server is encrypted.

When using connection encryption, the name (or IP address) in a Subject Common Name (CN) or Subject Alternative Name (SAN) in a SQL Server TLS/SSL certificate should exactly match the server name (or IP address) specified in the connection string. The HostnameInCertificate keyword (v18.0+) can be used to specify an alternate name used to match against the names in the TLS/SSL certificate. When the keyword is specified, the SQL Server TLS/SSL certificate must match either one of the server name, or the HostnameInCertificate.

By default, encrypted connections always verify the server's certificate. However, if you connect to a server that has a self-signed certificate, and aren't using strict encryption mode, you can add the TrustServerCertificate option to bypass checking the certificate against the list of trusted certificate authorities:

Driver={ODBC Driver 18 for SQL Server};Server=ServerNameHere;Encrypt=YES;TrustServerCertificate=YES  

In strict encryption mode, the certificate is always verified. As an option to standard certificate validation, the ServerCertificate keyword (v18.1+) can be used to specify the path to a certificate file to match against the SQL Server certificate. This option is only available when using strict encryption. The accepted certificate formats are PEM, DER, and CER. If specified, the SQL Server certificate is checked by seeing if the ServerCertificate provided is an exact match.

TLS on Linux and macOS uses the OpenSSL library. The following table shows the minimum supported versions of OpenSSL and the default Certificate Trust Store locations for each platform:

Platform Minimum OpenSSL Version Default Certificate Trust Store Location
Debian 10, 11 1.1.1 /etc/ssl/certs
Debian 9 1.1.0 /etc/ssl/certs
Debian 8.71 1.0.1 /etc/ssl/certs
OS X 10.11, macOS 1.0.2 /usr/local/etc/openssl/certs
Red Hat Enterprise Linux 9 3.0.1 /etc/pki/tls/cert.pem
Red Hat Enterprise Linux 8 1.1.1 /etc/pki/tls/cert.pem
Red Hat Enterprise Linux 7 1.0.1 /etc/pki/tls/cert.pem
Red Hat Enterprise Linux 6 1.0.0-10 /etc/pki/tls/cert.pem
SUSE Linux Enterprise 15 1.1.0 /etc/ssl/certs
SUSE Linux Enterprise 11, 12 1.0.1 /etc/ssl/certs
Ubuntu 22.04 3.0.2 /etc/ssl/certs
Ubuntu 20.04, 21.04, 21.10 1.1.1 /etc/ssl/certs
Ubuntu 18.04 1.1.0 /etc/ssl/certs
Ubuntu 16.04, 16.10, 17.10 1.0.2 /etc/ssl/certs
Ubuntu 14.04 1.0.1 /etc/ssl/certs

You can also specify encryption in the connection string using the Encrypt option when using SQLDriverConnect to connect.

Adjusting the TCP Keep-Alive Settings

Starting with ODBC Driver 17.4, how often the driver sends keep-alive packets and retransmits them when a response isn't received is configurable. To configure, add the following settings to either the driver's section in odbcinst.ini, or the DSN's section in odbc.ini. When connecting with a DSN, the driver will use the settings in the DSN's section if present; otherwise, or if connecting with a connection string only, it will use the settings in the driver's section in odbcinst.ini. If the setting isn't present in either location, the driver uses the default value. Beginning with ODBC Driver 17.8, KeepAlive and KeepAliveInterval keywords can be specified in the connection string.

  • KeepAlive=<integer> controls how often TCP attempts to verify that an idle connection is still intact by sending a keep-alive packet. The default is 30 seconds.

  • KeepAliveInterval=<integer> determines the interval separating keep-alive retransmissions until a response is received. The default is 1 second.

See Also