Troubleshoot SQL Server on Linux

Applies to: SQL Server (all supported versions) - Linux

This article describes how to troubleshoot SQL Server running on Linux or in a Docker container. When troubleshooting SQL Server on Linux, remember to review the supported features and known limitations in the SQL Server on Linux Release Notes.

For answers to frequently asked questions, see the SQL Server on Linux FAQ.

Troubleshoot connection failures

If you have difficulty connecting to your Linux SQL Server instance, there are a few things to check.

  • If you're unable to connect locally using localhost, try using the IP address 127.0.0.1 instead. It's possible that localhost isn't properly mapped to this address.

  • Verify that the server name or IP address is reachable from your client machine.

    Tip

    To find the IP address of your Ubuntu machine, you can run the ifconfig command as in the following example:

    sudo ifconfig eth0 | grep 'inet addr'
    

    For Red Hat, you can use the ip addr command as in the following example:

    sudo ip addr show eth0 | grep "inet"
    

    One exception to this technique relates to Azure VMs. For Azure VMs, find the public IP for the VM in the Azure portal.

  • If applicable, check that you opened the SQL Server port (default 1433) on the firewall.

  • For Azure VMs, check that you have a network security group rule for the default SQL Server port.

  • Verify that the user name and password don't contain any typos, extra spaces, or incorrect casing.

  • Try to explicitly set the protocol and port number with the server name like the following example: tcp:servername,1433.

  • Network connectivity issues can also cause connection errors and timeouts. After verifying your connection information and network connectivity, try the connection again.

Manage the SQL Server service

The following section shows how to manage the execution of SQL Server Docker containers. To manage services for Linux, see Start, stop, and restart SQL Server services on Linux.

Manage the execution of the SQL Server Docker container

You can get the status and container ID of the latest created SQL Server Docker container by running the following command (The ID is under the CONTAINER ID column):

sudo docker ps -l

You can stop or restart the SQL Server service as needed using the following commands:

sudo docker stop <container ID>
sudo docker restart <container ID>

Tip

For more troubleshooting tips for Docker, see Troubleshooting SQL Server Docker containers.

Access the log files

The SQL Server Database Engine logs to the /var/opt/mssql/log/errorlog file in both the Linux and Docker installations. You need to be in superuser mode to browse this directory.

The installer logs here: /var/opt/mssql/setup-<time stamp representing time of install> You can browse the errorlog files with any UTF-16 compatible tool like vim or cat like this:

sudo cat errorlog

If you prefer, you can also convert the files to UTF-8 to read them with more or less with the following command:

sudo iconv -f UTF-16LE -t UTF-8 <errorlog> -o <output errorlog file>

Extended events

Extended events can be queried via a SQL command. For more information, see extended events.

Crash dumps

Look for dumps in the log directory in Linux. Check under the /var/opt/mssql/log directory for Linux Core dumps (.tar.gz2 extension) or SQL minidumps (.mdmp extension)

For example, to view core dumps:

sudo ls /var/opt/mssql/log | grep .tar.gz2 

For SQL dumps, use this script:

sudo ls /var/opt/mssql/log | grep .mdmp 

Start SQL Server in minimal configuration or in single user mode

Start SQL Server in minimal configuration mode

This mode is useful if the setting of a configuration value (for example, over-committing memory) has prevented the server from starting.

sudo -u mssql /opt/mssql/bin/sqlservr -f

Start SQL Server in single user mode

Sometimes you may have to start an instance of SQL Server in single-user mode by using the startup option -m. For more information, see startup parameters. For example, you may want to change server configuration options or recover a damaged master database or other system database.

For example, use the following script to start SQL Server in single user mode:

sudo -u mssql /opt/mssql/bin/sqlservr -m

This script starts SQL Server in single user mode with sqlcmd:

sudo -u mssql /opt/mssql/bin/sqlservr -m sqlcmd

You should always start SQL Server on Linux with the mssql user to prevent future startup issues. For example: sudo -u mssql /opt/mssql/bin/sqlservr [STARTUP OPTIONS]

If you have accidentally started SQL Server with another user, you must change ownership of SQL Server database files back to the mssql user prior to starting SQL Server with systemd. For example, to change ownership of all database files under /var/opt/mssql to the mssql user, run the following command:

chown -R mssql:mssql /var/opt/mssql/

Rebuild system databases

As a last resort, you can choose to rebuild the master and model databases back to default versions.

This process is dangerous, because you will delete all SQL Server system data that you have configured, including information about your user databases (but not the user databases themselves). You will need to attach the user databases to the instance afterwards. It will also delete other information stored in the system databases, including:

  • Database Master Key information
  • any certificates loaded in master
  • the SA login password
  • job-related information from msdb
  • Database Mail information from msdb
  • sp_configure options

You won't be able to reattach any user databases encrypted with Transparent Data Encryption (TDE) unless your certificates and private keys are also backed up.

Only use these steps if you understand the implications.

  1. Stop SQL Server Database Engine

    sudo systemctl stop mssql-server
    
  2. Run sqlservr with the force-setup parameter

    sudo -u mssql /opt/mssql/bin/sqlservr --force-setup
    

    You should always start SQL Server on Linux with the mssql user to prevent future startup issues.

  3. After you see the message "Recovery is complete", press Ctrl+C. This will shut down SQL Server.

  4. Reconfigure the SA password.

    sudo /opt/mssql/bin/mssql-conf set-sa-password
    
  5. Start SQL Server and reconfigure the server, including restoring or reattaching any user databases.

    sudo systemctl start mssql-server
    

Improve performance

Many factors affect performance, including database design, hardware, and workload demands. If you're looking to improve performance, start by reviewing the best practices in the article, Performance best practices and configuration guidelines for SQL Server on Linux. Then explore some of the available tools for troubleshooting performance problems.

Common issues

  1. You can't connect to your remote SQL Server instance.

    See the troubleshooting section of the article, Connect to SQL Server on Linux.

  2. You experience the error message: ERROR: Hostname must be 15 characters or less.

    This is a known issue that happens whenever the name of the machine that is trying to install the SQL Server package is longer than 15 characters. There are currently no workarounds other than changing the name of the machine. You can edit the hostname file and reboot the machine, which is explained in detail in the following website guide.

  3. The system administration (SA) password must be reset, which will stop the SQL Server service temporarily.

    If you forget the system administrator (SA) password or need to reset it for some other reason, follow these steps.

    Log into the host terminal, run the following commands and follow the prompts to reset the SA password:

    sudo systemctl stop mssql-server
    sudo /opt/mssql/bin/mssql-conf setup
    
  4. Special characters in login passwords cause errors or login failures.

    If you use some characters in the SQL Server login password, you might need to escape them with a backslash when you use them on the Linux command line. For example, you must escape the dollar sign ($) anytime you use it in a terminal command/shell script:

    Does not work:

    sudo sqlcmd -S myserver -U sa -P Test$$
    

    Does work:

    sqlcmd -S myserver -U sa -P Test\$\$
    

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