Init RC Files in AOSP

.rc files are read by the init process (PID 1) very early in the Android boot sequence. They define which services to start, which file systems to mount, what properties to set, and what actions to trigger when certain events happen. Understanding .rc files is essential for anyone working on AOSP daemons or boot customization.

Where RC Files Live

• ▸system/core/rootdir/init.rc - the main init.rc, part of AOSP core
• ▸device/<manufacturer>/<device>/init.<device>.rc - device-specific init file
• ▸vendor/etc/init/ - vendor service declarations (loaded from /vendor partition)
• ▸system/etc/init/ - system service declarations
• ▸Each .rc file is scanned and merged by init at boot

RC File Syntax

  # ── SERVICE DEFINITION ───────────────────────
  service adbd /system/bin/adbd
      class core                 # service class group
      socket adbd stream 660 system system
      disabled                   # don't start automatically
      seclabel u:r:adbd:s0       # SELinux label

  # ── ACTION / TRIGGER ─────────────────────────
  on early-init
      setprop sys.init.early 1

  on property:sys.boot_completed=1
      start myvendordaemon

  # ── IMPORT OTHER RC FILES ────────────────────
  import /vendor/etc/init/myhal.rc

Service Options

• ▸class <name> - groups services; 'class_start core' starts all services in the 'core' class
• ▸oneshot - service runs once and exits (not restarted)
• ▸restart_backoff - how long to wait before restarting a crashed service
• ▸user / group - Linux user and group the service runs as
• ▸capabilities - Linux capabilities granted to the service (e.g. NET_ADMIN)
• ▸socket <name> <type> <perm> - creates a Unix domain socket for the service
• ▸file <path> <type> - opens a file and passes the fd to the service

Init Triggers (Actions)

• ▸on early-init - very first stage, minimal filesystem available
• ▸on init - basic setup, /proc and /sys mounted
• ▸on late-init - most services started here
• ▸on boot - triggered after late-init, network interfaces starting
• ▸on property:<key>=<value> - triggered when a property changes to that value
• ▸on fs - triggered when filesystems are being mounted