v0.0.1 (#8)

Co-authored-by: Tasnim Kabir Sadik <tksadik92@gmail.com>
Reviewed-on: wrenn/sandbox#8

images/wrenn-init.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 # wrenn-init: minimal PID 1 init for Firecracker microVMs.
-# Mounts virtual filesystems then execs envd.
+# Mounts virtual filesystems, starts chronyd for time sync, then execs tini + envd.
 
 set -e
 
@@ -15,16 +15,37 @@ mount -t tmpfs tmpfs /tmp 2>/dev/null || true
 mount -t tmpfs tmpfs /run 2>/dev/null || true
 mkdir -p /sys/fs/cgroup
 mount -t cgroup2 cgroup2 /sys/fs/cgroup 2>/dev/null || true
+echo "+cpu +memory +io" > /sys/fs/cgroup/cgroup.subtree_control 2>/dev/null || true
 
 # Set hostname
 hostname sandbox
 
+# Configure networking if the kernel ip= boot arg did not already set it up.
+if ! ip addr show eth0 2>/dev/null | grep -q "169.254.0.21"; then
+    ip link set lo up 2>/dev/null || true
+    ip link set eth0 up 2>/dev/null || true
+    ip addr add 169.254.0.21/30 dev eth0 2>/dev/null || true
+    ip route add default via 169.254.0.22 2>/dev/null || true
+fi
+
 # Configure DNS resolver.
 echo "nameserver 8.8.8.8" > /etc/resolv.conf
 echo "nameserver 8.8.4.4" >> /etc/resolv.conf
 
 # Set a standard PATH so envd and all child processes can find common binaries.
-export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
+
+# Write chrony config to sync time from the KVM PTP hardware clock.
+# /dev/ptp0 is a paravirtual clock exposed by KVM — no network required.
+mkdir -p /etc/chrony /run/chrony
+cat > /etc/chrony/chrony.conf <<EOF
+refclock PHC /dev/ptp0 poll 2 dpoll 2
+driftfile /run/chrony/chrony.drift
+makestep 1.0 -1
+EOF
+
+# Start chronyd in the background before handing off to tini.
+chronyd -f /etc/chrony/chrony.conf 2>/dev/null || true
 
 # Exec tini as PID 1 — it reaps zombie processes and forwards signals to envd.
 exec /sbin/tini -- /usr/local/bin/envd