pgloader fails to connect to MSSQL with "Connection to the database failed for an unknown reason" while tsql succeeds

[AhmdFahad]

Description

pgloader fails to connect to a Microsoft SQL Server instance with an "unknown reason" error, even though the same credentials and host work successfully with tsql.

This suggests either a connection string handling issue, hostname resolution problem, or a driver compatibility problem.

Environment

• pgloader version: 3.6.3~devel
• OS: Ubuntu (WSL)
• MSSQL Server: SQL Server on localhost
• Connection method: TCP port 1433
• Target: PostgreSQL 5432 (localhost)

pgloader command

pgloader migration.load

migration.load contents

LOAD DATABASE
     FROM mssql://sa:p@ssw0rd@SQLSERVER:1433/IMORE_DAFTAR_QE
     INTO pgsql://postgres@localhost:5432/IMORE_DAFTAR_QE;

pgloader output

2026-02-16T14:00:57.008001Z LOG pgloader version "3.6.3~devel"
2026-02-16T14:00:57.080006Z LOG Migrating from mssql://sa@SQLSERVER:1433/IMORE_DAFTAR_QE
2026-02-16T14:01:07.115432Z ERROR mssql: Failed to connect to mssql at "SQLSERVER" (port 1433) as user "sa": Connection to the database failed for an unknown reason.

tsql test (successful)

tsql -H 127.0.0.1 -p 1433 -U sa -P 'p@ssw0rd'

Output:

locale is "C"
locale charset is "ANSI_X3.4-1968"
using default charset "UTF-8"
1> exit

This confirms:

• SQL Server is running
• Credentials are valid
• Network connectivity works

Expected behavior

pgloader should connect successfully to MSSQL using the same credentials.

Actual behavior

pgloader fails with:

Connection to the database failed for an unknown reason.

Request

Please advise recommended configuration or troubleshooting steps.

Thanks