varnishlog

varnishlog [-c] [-b] [-q query] [-i tag] [options]

varnishlog reads the Varnish Shared Memory Log (VSL) and displays detailed request and response information in real time. It shows the full lifecycle of HTTP transactions including client requests, backend fetches, cache decisions, and response headers.The tool provides powerful filtering through the VSL query language, allowing you to isolate specific transactions by status code, URL pattern, or any logged field. Client-side (-c) and backend-side (-b) views can be shown independently, and grouping modes organize output by request, session, or raw log entries. This makes it the primary debugging tool for understanding Varnish cache behavior.

-c

Show client-side transactions only.

Show backend-side transactions only.

VSL query expression to filter transactions.

Include only records with specified tags (comma-separated).

Include only records matching tag and regex pattern.

Exclude records with specified tags.

Exclude records matching tag and regex pattern.

Grouping mode (raw, vxid, request, session).

Process old log entries first.

Write output to file.

Requires a running Varnish instance. Familiarity with VSL query language is helpful for effective filtering. Output can be very verbose without filters.

varnishlog is part of Varnish Cache, displaying the Varnish Shared Memory Log for debugging.

varnishhist(1), varnishstat(1), varnishd(1)