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secure-network: fix intermittent DNS failure on Ubuntu runners (resolv.conf symlink) #175

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secure-network: fix intermittent DNS failure on Ubuntu runners (resolv.conf symlink) #175

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5 changes: 5 additions & 0 deletions .changeset/secure-network-symlink-fix.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"secure-network": patch
---

Fix intermittent DNS failures on GitHub-hosted runners caused by /etc/resolv.conf being a symlink to a tmpfs file managed by systemd-resolved. chattr +i is a no-op on tmpfs, so systemd-resolved could overwrite the file after setup. The symlink is now removed before writing, creating a real file on /etc (ext4) that chattr can lock.
15 changes: 15 additions & 0 deletions actions/secure-network/secure-network.js
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Expand Up @@ -546,6 +546,21 @@ async function main() {
}

console.log("Redirecting DNS to local Unbound resolver...");
// On Ubuntu with systemd-resolved, /etc/resolv.conf is a symlink to
// /run/systemd/resolve/stub-resolv.conf on tmpfs. Writing through the symlink
// lets systemd-resolved silently overwrite our change, and chattr +i is a
// no-op on tmpfs (unsupported filesystem). Remove any existing symlink/file
// first so we create a real file on /etc (ext4), where chattr can lock it.
try {
if (fs.lstatSync("/etc/resolv.conf").isSymbolicLink()) {
fs.unlinkSync("/etc/resolv.conf");
console.log(
" Removed /etc/resolv.conf symlink (was managed by systemd-resolved).",
);
}
} catch (_) {
/* not a symlink or doesn't exist — proceed */
}
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@jaredly jaredly Apr 14, 2026

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this catch feels a little over-general -- if we want the "doesn't exist" case, we could fo fs.existsSync(path) && fs.lstatSync(path).isSymbolicLink()

fs.writeFileSync("/etc/resolv.conf", "nameserver 127.0.0.1\n");
// resolv.conf.bak is kept until process exit; the exit handler restores it on error.

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