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Make SQLite temp files work on a read-only root #1972
Description
SQLite writes temp files (sorts, temp B-trees, large transactions) to a directory that the unix VFS chooses: SQLITE_TMPDIR, then TMPDIR, then /var/tmp, /usr/tmp, /tmp and .. It reads the two environment variables once, at OS init. On a container with a read-only root filesystem, none of the default directories may be writable, so a large import can fail.
Make the temp directory a deployment setting, not code in gtfsdb. For example, set TMPDIR (or SQLITE_TMPDIR) to a writable volume in the Dockerfile and the docker-compose files, and document it in the README. Setting the variable from createDB is not reliable, because SQLite reads it only once per process.
Found in review of #1677, which keeps the default file-backed temp storage (temp_store is not changed).
Activity
Ashu-300 commentedon Nov 9, 2026
Hi @aaronbrethorst ,
I noticed this is self-assigned—are you currently working on this, or would you like me to open a PR?
I have the proposed changes drafted:
Dockerfile & Dockerfile.dev: Ensure /app/data/tmp exists with proper ownership (chown -R maglev:maglev), and set ENV TMPDIR=/app/data/tmp so SQLite directs temp spill files to the writable volume instead of the read-only root /tmp.
Docker Compose: Add TMPDIR: /app/data/tmp to the environment: section in both docker-compose.yml and docker-compose.dev.yml.
Documentation: Update README.markdown to document deployment guidance for read-only root container environments.
Happy to open a PR with these updates if you'd like!