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fix(vm): populate an empty guest /etc/hosts with loopback names - #4182
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OCI images commonly ship an empty /etc/hosts and rely on the container runtime to bind-mount a generated one. The VM driver does not, and guest init wrote /etc/hostname and /etc/resolv.conf but never /etc/hosts, so localhost did not resolve: the guest resolver is the loopback relay, which has no record for it. Add configure_hosts to guest init, called after configure_hostname. It writes IPv4 and IPv6 localhost entries when the file is missing or empty, keeps a non-empty file and leaves a symlink alone, because an absolute link target would resolve against init's own root. A write failure logs a warning and boot continues. Cover the file states and the boot-path call site with tests that run the shipped init function under bash. Closes NVIDIA#3934 Signed-off-by: Shiju <shiju@nvidia.com>
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October 4, 2026 12:02
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Summary
A MicroVM sandbox started from an OCI image that ships an empty
/etc/hostskeeps that empty file, solocalhostdoes not resolve inside the guest. The guest init now writes the loopback names when the file is missing or empty. It leaves a non-empty file and a symlink alone.The change covers empty or missing files only. An image that ships a non-empty hosts file with no
localhostline, or only comments, is still left as the author wrote it, solocalhostcan still fail to resolve for those images.Related Issue
Closes #3934.
Changes
crates/openshell-driver-vm/scripts/openshell-vm-sandbox-init.sh: addconfigure_hosts, called right afterconfigure_hostnameinrun_post_overlay_setup. It returns without writing when/etc/hostsis a symlink (logging a warning) or is non-empty. Otherwise it writes127.0.0.1 localhostand::1 localhost ip6-localhost ip6-loopback. A write failure logs a warning, lets the shell's own error reach the console, and boot continues, because missing loopback names degrade the workload but do not weaken isolation.crates/openshell-driver-vm/src/rootfs.rs: two tests.guest_init_populates_missing_or_empty_hosts_and_keeps_image_hostscuts the realconfigure_hostsout of the shipped script and runs it underbashagainst a temporary root for a missing file, an empty file, an image-authored file, and a symlink to a file outside the root.guest_init_boot_path_configures_hosts_after_the_account_and_before_networkingchecks thatrun_post_overlay_setupitself callsconfigure_hostsafterreconcile_sandbox_accountand before the network step.Testing
Checklist