Public bug reported:
When casper netboots via url= / iso-url=, do_urlmount() fetches the whole
installer ISO using the wget in the initramfs, which sends its default header:
User-Agent: Wget
That is the bare busybox default - no product name, no version. For a mirror
operator it is unusable: the traffic can't be counted, and it can't be rate
limited or shaped without also hitting every other busybox wget on the
internet.
I got complaint from my friend who operates a Ubuntu mirror in my country.
Everything else we ship identifies itself. Measured on resolute:
apt Debian APT-HTTP/1.3 (3.2.0) non-interactive
cloud-init Cloud-Init/<version>
curl curl/8.18.0
GNU wget Wget/1.25.0
casper Wget
It is not a small amount of traffic to be blind to. Each fetch is the entire
ISO - 2.7G for the 26.04 live-server image, 6.1G for desktop - there is no -c,
and the image is only validated (is_casper_path, matches_uuid) after it has
been downloaded in full. So a kernel/initrd/ISO version mismatch, which the
s390x installation docs warn about explicitly, costs the mirror the whole
transfer, and in the interactive netboot fallback the user can repeat that as
often as they like.
There is a failure mode in this for us too. A generic user agent is a
plausible target for bot protection, and if the fetch fails on this path
mountroot() panics in the initramfs with no fallback. That is not
hypothetical - in May 2026 Cloudflare on archive.ubuntu.com blocked pycurl's
default user agent and broke Linux Mint's mirror checks entirely:
https://github.com/linuxmint/mintsources/issues/276
apt had the same request in LP #1825000 and solved it by adding a word to its
User-Agent. I would like to do the equivalent here: send
"casper/<version> (<arch>)", with "interactive" appended when we arrived
through do_interactive_netmount(), so that automated netboots can be told
apart from someone retrying by hand at the prompt.
** Affects: casper (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2164828
Title:
casper sends no identifiable User-Agent when downloading an ISO
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