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Enable and run tempdb on tmpfs for SQL Server 2025 on Linux

Applies to: SQL Server 2025 (17.x) on Linux

This article guides you to enable and run tempdb database files on the tmpfs filesystem in SQL Server 2025 (17.x).

SQL Server on Linux and containers traditionally support XFS and ext4 filesystems for deploying SQL Server database files and logs. However, for temporary databases like tempdb, which don't require data to be saved from one uptime period to another, using a tmpfs filesystem that utilizes memory (RAM) can enhance overall performance for tempdb-based workloads.

For more information about the tmpfs filesystem, see tmpfs - The Linux Kernel documentation.

Configuration Description
Supported configuration tmpfs is ideal for storing non-persistent data that doesn't need to be saved across restarts. Currently only the tempdb database files are supported on tmpfs filesystem for both container and non-container based deployments.
Unsupported configuration tmpfs filesystem can be used for user databases in SQL container deployments, but only for development purposes. However, this configuration isn't supported. You can provide feedback for this scenario on GitHub.

Physical or virtual machine deployments

To enable tmpfs support for SQL Server on Linux on physical or virtual machines, you need to mount the tmpfs filesystem correctly, which requires sudo access. Once the mount points are set up, you can place the tempdb files on these mounts and start SQL Server with tempdb files mounted on the tmpfs filesystem.

Enable tmpfs for tempdb

  1. Create the tempdb directory.

    Use the mkdir command to create a directory for the tempdb database. Ensure that it's owned by the mssql user and group to allow SQL Server access:

    sudo mkdir /var/opt/mssql/tempdb
sudo chown mssql. /var/opt/mssql/tempdb

  2. Mount the tmpfs filesystem.

    Use the following command to mount the tmpfs filesystem:

    sudo mount -t tmpfs -o size=4G tmpfs /var/opt/mssql/tempdb/

    The -t option specifies the type of filesystem, which in this case is tmpfs.

    The -o option allows you to specify mount options. Here, size=4G sets the maximum size of the tmpfs to 4 GB, meaning it can use up to 4 GB of RAM.

    This command mounts tmpfs to the target directory used by SQL Server tempdb database.

    Optionally, add it to fstab to maintain the mounts across restarts:

    echo "tmpfs /var/opt/mssql/tempdb tmpfs defaults,size=4G 0 0" | sudo tee -a /etc/fstab

  3. Update tempdb file location.

    Ensure SQL Server is up and running. Connect to your SQL Server instance using SQL Server Management Studio (SSMS), and run the following Transact-SQL (T-SQL) commands.

    Identify all the tempdb files using the following T-SQL script, then run the ALTER DATABASE command to update the tempdb file location:

    SELECT [name],
       physical_name
FROM sys.master_files
WHERE database_id = 2;

    Based on the number of files you see for tempdb, you create the ALTER DATABASE commands as follows:

    ALTER DATABASE tempdb
    MODIFY FILE (NAME = tempdev, FILENAME = '/var/opt/mssql/tempdb/tempdb.mdf');

ALTER DATABASE tempdb
    MODIFY FILE (NAME = tempdev2, FILENAME = '/var/opt/mssql/tempdb/tempdb2.mdf');

ALTER DATABASE tempdb
    MODIFY FILE (NAME = tempdev3, FILENAME = '/var/opt/mssql/tempdb/tempdb3.mdf');

ALTER DATABASE tempdb
    MODIFY FILE (NAME = tempdev4, FILENAME = '/var/opt/mssql/tempdb/tempdb4.mdf');

ALTER DATABASE tempdb
    MODIFY FILE (NAME = templog, FILENAME = '/var/opt/mssql/tempdb/templog.ldf');

  4. Restart SQL Server to apply the changes.

    sudo systemctl restart mssql-server

  5. Verify tempdb file locations.

    Once SQL Server is up and running, verify that the tempdb data and log files are now located in the new directory by connecting to SQL Server using a tool like SSMS.

    SELECT [name],
       physical_name
FROM sys.master_files
WHERE database_id = 2;

You should now see all the tempdb database files on the new mount path that is /var/opt/mssql/tempdb.

Hot resizing of the tmpfs mount

You can also hot-resize the tmpfs mount in case the tempdb is full. To hot-resize, run the following command to resize the tmpfs mount to 6 GB:

sudo mount -o remount,size=6G /var/opt/mssql/tempdb

Optionally, make the new size persist across restarts by modifying the fstab entry:

sudo sed -i 's|tmpfs /var/opt/mssql/tempdb tmpfs defaults,size=4G 0 0|tmpfs /var/opt/mssql/tempdb tmpfs defaults,size=6G 0 0|' /etc/fstab

Container deployments

For developer workloads, tmpfs can be used for user databases. tmpfs filesystems can significantly speed up test cases for user databases deployed in containers. Since tmpfs uses RAM instead of disk storage, it allows for rapid read/write operations. This configuration is useful in development and testing environments where quick iterations are needed.

However, tmpfs for user databases is not supported. You can provide feedback related to user databases on tmpfs on GitHub.

Host only the tempdb database on the tmpfs filesystem

If you're deploying a SQL Server container and want to ensure that the container uses tmpfs for the tempdb, you can run the following command:

docker run \
  -e ACCEPT_EULA=Y \
  -e 'MSSQL_SA_PASSWORD=<password>' \
  --tmpfs /var/opt/mssql/tempdb:uid=10001,gid=10001,size=4G \
  -p 5433:1433 \
  --name sql1 \
  -h sql1 \
  -d mcr.microsoft.com/mssql/server:2025-latest

The --tmpfs option sets the size to 4 GB and the uid (user ID) and gid (group ID) to 10001 to ensure that the required permissions are set correctly for the tempdb files to be created.

Once the container is up and running, connect to the SQL Server instance using SSMS, and update the tempdb file locations to /var/opt/mssql/tempdb with the following T-SQL commands:

SELECT [name],
       physical_name
FROM sys.master_files
WHERE database_id = 2;

Based on the number of files that you see, modify the following command. In this example, there are four tempdb data files and one log file. Use the following commands to update the file locations:

ALTER DATABASE tempdb
MODIFY FILE (NAME = tempdev, FILENAME = '/var/opt/mssql/tempdb/tempdb.mdf');
GO

ALTER DATABASE tempdb
MODIFY FILE (NAME = tempdev2, FILENAME = '/var/opt/mssql/tempdb/tempdb2.mdf');
GO

ALTER DATABASE tempdb
MODIFY FILE (NAME = tempdev3, FILENAME = '/var/opt/mssql/tempdb/tempdb3.mdf');
GO

ALTER DATABASE tempdb
MODIFY FILE (NAME = tempdev4, FILENAME = '/var/opt/mssql/tempdb/tempdb4.mdf');
GO

ALTER DATABASE tempdb
MODIFY FILE (NAME = templog, FILENAME = '/var/opt/mssql/tempdb/templog.ldf');
GO

After you update the file locations, stop and restart the container using the following commands:

docker stop sql1
docker start sql1

Deploy containers with all data and log files on tmpfs

Warning

This configuration isn't supported, but can be used for development purposes. You can provide feedback for this scenario on GitHub.

docker run -e ACCEPT_EULA=Y \
  -e 'MSSQL_SA_PASSWORD=<password>' \
  --tmpfs /var/opt/mssql/data:uid=10001,gid=10001,size=4G \
  -p 5434:1433 \
  --name sql2 \
  -h sql2 \
  -d mcr.microsoft.com/mssql/server:2025-latest

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