Package: dhcpcd-base Version: 1:10.1.0-11+deb13u3 Severity: normal resolvconf will silently fail to update (replace) the contents of /etc/resolv.conf when running as a dhcpcd hook. It will leave /etc/resolv.conf with the empty template that was generated prior to dhcpcd starting, with no 'nameserver' entry, therefore having glibc default to 127.0.0.1 as its nameserver.
When resolvconf is installed, the 20-resolv.conf dhcpcd hook will invoke it instead of writing /etc/resolv.conf on its own (have_resolvconf=true). resolvconf sets up /etc/resolv.conf as a symlink to /run/resolvconf/resolv.conf. After generating its temporary copy of resolv.conf, it does a rename to replace /run/resolvconf/resolv.conf. The systemd unit file for dhcpcd sets up a sandbox and adds /etc/resolv.conf to the list of ReadWritePaths=, which makes sense since in the default configuration, /etc/resolv.conf is not a symlink. However, with resolvconf installed, ReadWritePaths="... /etc/resolv.conf" resolves to a bind-mount of /run/resolvconf/resolv.conf in dhcpcd's namespace, and any attempt by resolvconf (running as a hook in that namespace) to mv over it results in EBUSY, causing resolvconf to fail: + mv -f /run/resolvconf/resolv.conf_new.1844 /run/resolvconf/resolv.conf mv: cannot move '/run/resolvconf/resolv.conf_new.1844' to '/run/resolvconf/resolv.conf': Device or resource busy For my own setup, I did an override of the systemd unit file and removed /etc/resolv.conf from ReadWritePaths since /run is already writable (not sure how given that ProtectSystem=strict is set; /etc and /usr are correctly read-only), so resolvconf can properly regenerate the target. But that would not work in the default case since /etc/resolv.conf would still be a static file under /etc, which _is_ read-only inside the sandbox. I saw #1133083 mentions dhcpcd should do like resolvconf (and systemd-resolved, and others), and manage a symlink instead of a static /etc/resolv.conf, which could be one way to fix this. Or some way to conditionally add /etc/resolv.conf to ReadWritePaths=. -- System Information: Debian Release: 13.6 APT prefers stable-updates APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable') Architecture: amd64 (x86_64) Kernel: Linux 6.12.101+deb13-amd64 (SMP w/12 CPU threads; PREEMPT) Kernel taint flags: TAINT_USER Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set Shell: /bin/sh linked to /usr/bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages dhcpcd-base depends on: ii adduser 3.152 ii libc6 2.41-12+deb13u3 ii libssl3t64 3.5.6-1~deb13u2 ii libudev1 257.13-1~deb13u1 dhcpcd-base recommends no packages. Versions of packages dhcpcd-base suggests: ii resolvconf 1.94 -- Configuration Files: /etc/dhcpcd.conf changed: hostname clientid persistent vendorclassid option domain_name_servers, domain_name, domain_search option captive_portal_uri option classless_static_routes option interface_mtu option host_name option ntp_servers require dhcp_server_identifier slaac private -- no debconf information
