Android开机启动过程 - Android资料 - 移动互联网学院（华清远见旗下品牌）

Android开机启动过程

分享到：

和大多数Linux发行版一样，在执行开机后，Android也是通过引导加载器（bootloader）首先将Linux内核装载到内存中，然后启动初始化进程。初始化进程在完成一系列初始化工作后，会启动相关的守护进程、Zygote虚拟机和相关的实时进程，进而完成整个启动过程。图1-1显示了Android在启动过程中各进程的启动顺序。

图1-1 Android的启动过程
图1-1 Android的启动过程

在启动system\core\rootdir\init.rc脚本后，会首先创建系统运行所需的各种环境变量，接着创建各种文件系统（如系统文件系统、用户文件系统、SD Card、缓存（Cache）等）的挂载点，并将这些文件系统挂载到MTD（Memory Technology Device）上。

然后会为接下来的守护进程和实时进程的创建做些准备，如设置进程的内存门槛、系统服务和守护进程的权限等，并为各种网络（如WIFI、UMTS、EDGE、GPRS、CDMA（Android 1.6后支持）等）设置所需的TCP缓存，然后即创建各种守护进程，具体初始化过程如下：

初始化过程

on init
    sysclktz 0 //设置系统时区
    loglevel 3 //日志级别
    # 设置全局环境变量
      export PATH /sbin:/system/sbin:/system/bin:/system/xbin //设置环境变量
      export LD_LIBRARY_PATH /system/lib //共享库路径
      export ANDROID_BOOTLOGO 1
      export ANDROID_ROOT /system //根路径
      export ANDROID_ASSETS /system/app
      export ANDROID_DATA /data
      export EXTERNAL_STORAGE /sdcard //SD卡
      export BOOTCLASSPATH
      /system/framework/core.jar:/system/framework/ext.jar:/system/framework/
      framework.jar:/system/framework/android.policy.jar:/system/framework/services.jar //核心库
    # 后向兼容
      symlink /system/etc /etc
    #创建挂载点并将tmpfs挂载到sqlite_stmt_journals上
      mkdir /sdcard 0000 system system
      mkdir /system
      mkdir /data 0771 system system
      mkdir /cache 0770 system cache
      mkdir /sqlite_stmt_journals 01777 root root
      mount tmpfs tmpfs /sqlite_stmt_journals size=4m
      mount rootfs rootfs / ro remount
      write /proc/sys/kernel/panic_on_oops 1
      write /proc/sys/kernel/hung_task_timeout_secs 0
      write /proc/cpu/alignment 4
      write /proc/sys/kernel/sched_latency_ns 10000000
      write /proc/sys/kernel/sched_wakeup_granularity_ns 2000000
    # 挂载MTD分区
      # 首先挂载System分区以保存文件系统检查点
      mount yaffs2 mtd@system /system //挂载yaffs2文件系统
      mount yaffs2 mtd@system /system ro remount
      # 挂载Data分区，设置权限
      mount yaffs2 mtd@userdata /data nosuid nodev
      chown system system /data
      chmod 0771 /data
      # 挂载Cache分区，并设置权限
      mount yaffs2 mtd@cache /cache nosuid nodev
      chown system cache /cache
      chmod 0770 /cache
      # 设置修复路径权限
      chown system system /cache/recovery
      chmod 0770 /cache/recovery
    # 创建基本的文件系统结构
      mkdir /data/misc 01771 system misc
      mkdir /data/misc/hcid 0770 bluetooth bluetooth
      mkdir /data/local 0771 shell shell
      mkdir /data/local/tmp 0771 shell shell
      mkdir /data/data 0771 system system
      mkdir /data/app-private 0771 system system
      mkdir /data/app 0771 system system
      mkdir /data/property 0700 root root
      # 配置dalvik-cache权限
      mkdir /data/dalvik-cache 0771 system system
      chown system system /data/dalvik-cache
      chmod 0771 /data/dalvik-cache
      # 创建lost+found目录
      mkdir /data/lost+found 0770
      mkdir /cache/lost+found 0770
      # 配置lost+found权限
      chown root root /data/lost+found
      chmod 0770 /data/lost+found
      chown root root /cache/lost+found
      chmod 0770 /cache/lost+found
    on boot
    # 基本网络初始化
      ifup lo
      hostname localhost
      domainname localdomain
    # 设置RLIMIT_NICE，使优先级范围为19～-20
      setrlimit 13 40 40
    # 设置rmnet超时值
      write /sys/devices/virtual/net/rmnet0/timeout_suspend 5000000
    //定义ActivityManagerService 用到的系统属性
      setprop ro.FOREGROUND_APP_ADJ 0
      setprop ro.VISIBLE_APP_ADJ 1
      setprop ro.SECONDARY_SERVER_ADJ 2
      setprop ro.HOME_APP_ADJ 4
      setprop ro.HIDDEN_APP_MIN_ADJ 7
      setprop ro.CONTENT_PROVIDER_ADJ 14
      setprop ro.EMPTY_APP_ADJ 15
    //定义垃圾回收用到的内存门槛
      setprop ro.FOREGROUND_APP_MEM 1536
      setprop ro.VISIBLE_APP_MEM 2048
      setprop ro.SECONDARY_SERVER_MEM 4096
      setprop ro.HOME_APP_MEM 4096
      setprop ro.HIDDEN_APP_MEM 5120
      setprop ro.CONTENT_PROVIDER_MEM 5632
      setprop ro.EMPTY_APP_MEM 6144
      write /sys/module/lowmemorykiller/parameters/adj 0,1,2,7,14,15
      write /proc/sys/vm/overcommit_memory 1
      write /proc/sys/vm/min_free_order_shift 4
      write /sys/module/lowmemorykiller/parameters/minfree 1536,2048,4096,5120,5632,6144
        #设置init进程能够创建的子进程的数量
      write /proc/1/oom_adj -16
        #设置系统服务和守护进程的权限
      chown radio system /sys/android_power/state
      chown radio system /sys/android_power/request_state
      chown radio system /sys/android_power/acquire_full_wake_lock
      chown radio system /sys/android_power/acquire_partial_wake_lock
      chown radio system /sys/android_power/release_wake_lock
      chown radio system /sys/power/state
      chown radio system /sys/power/wake_lock
      chown radio system /sys/power/wake_unlock
      chmod 0660 /sys/power/state
      chmod 0660 /sys/power/wake_lock
      chmod 0660 /sys/power/wake_unlock
      chown system system /sys/class/timed_output/vibrator/enable
      chown system system /sys/class/leds/keyboard-backlight/brightness
      chown system system /sys/class/leds/lcd-backlight/brightness
      chown system system /sys/class/leds/button-backlight/brightness
      chown system system /sys/class/leds/jogball-backlight/brightness
      chown system system /sys/class/leds/red/brightness
      chown system system /sys/class/leds/green/brightness
      chown system system /sys/class/leds/blue/brightness
      chown system system /sys/class/leds/red/device/grpfreq
      chown system system /sys/class/leds/red/device/grppwm
      chown system system /sys/class/leds/red/device/blink
      chown system system /sys/class/leds/red/brightness
      chown system system /sys/class/leds/green/brightness
      chown system system /sys/class/leds/blue/brightness
      chown system system /sys/class/leds/red/device/grpfreq
      chown system system /sys/class/leds/red/device/grppwm
      chown system system /sys/class/leds/red/device/blink
      chown system system /sys/class/timed_output/vibrator/enable
      chown system system /sys/module/sco/parameters/disable_esco
      chown system system /sys/kernel/ipv4/tcp_wmem_min
      chown system system /sys/kernel/ipv4/tcp_wmem_def
      chown system system /sys/kernel/ipv4/tcp_wmem_max
      chown system system /sys/kernel/ipv4/tcp_rmem_min
      chown system system /sys/kernel/ipv4/tcp_rmem_def
      chown system system /sys/kernel/ipv4/tcp_rmem_max
      chown root radio /proc/cmdline
    #定义各种网络情况下的TCP缓冲
    # ReadMin, ReadInitial, ReadMax, WriteMin, WriteInitial, WriteMax,
      setprop net.tcp.buffersize.default 4096,87380,110208,4096,16384,110208
      setprop net.tcp.buffersize.wifi 4095,87380,110208,4096,16384,110208
      setprop net.tcp.buffersize.umts 4094,87380,110208,4096,16384,110208
      setprop net.tcp.buffersize.edge 4093,26280,35040,4096,16384,35040
      setprop net.tcp.buffersize.gprs 4092,8760,11680,4096,8760,11680
      class_start default
    # 初始化守护进程
    service console /system/bin/sh //启动Shell
      console
    # adbd由persist.service.adb.enable系统属性控制
    service adbd /sbin/adbd //启动adb守护进程
      disabled
    on property:ro.kernel.qemu=1
      start adbd
    on property:persist.service.adb.enable=1
      start adbd
    on property:persist.service.adb.enable=0
      stop adbd
    service servicemanager /system/bin/servicemanager //启动IBinder通信
      user system
      critical
      onrestart restart zygote
      onrestart restart media
    service vold /system/bin/vold
      socket vold stream 0660 root mount
    service debuggerd /system/bin/debuggerd //启动调试系统
    service ril-daemon /system/bin/rild //启动RIL（Radio Interface Layer）守护进程
      socket rild stream 660 root radio
      socket rild-debug stream 660 radio system
      user root //root用户权限
      group radio cache inet misc
    service zygote /system/bin/app_process -Xzygote/
    system/bin --zygote --start-system-server
      socket zygote stream 666
      onrestart write /sys/android_power/request_state wake
      onrestart write /sys/power/state on
    service media /system/bin/mediaserver //启动音频管理器等媒体服务
      user media
      group system audio camera graphics inet net_bt net_bt_admin
    service bootsound /system/bin/playmp3 //启动开机音乐
      user media
      group audio
      oneshot
    service dbus /system/bin/dbus-daemon --system –nofork //启动Dbus守护进程
      socket dbus stream 660 bluetooth bluetooth
      user bluetooth
      group bluetooth net_bt_admin
    service hcid /system/bin/hcid -s -n -f /etc/bluez/hcid.conf //重定向hcid
      socket bluetooth stream 660 bluetooth bluetooth
      socket dbus_bluetooth stream 660 bluetooth bluetooth
      group bluetooth net_bt_admin misc
      disabled
    service hfag /system/bin/sdptool add --channel=10 HFAG //启动蓝牙免提音频网关
      user bluetooth
      group bluetooth net_bt_admin
      disabled
      oneshot
    service hsag /system/bin/sdptool add --channel=11 HSAG //启动蓝牙耳机音频网关
      user bluetooth
      group bluetooth net_bt_admin
      disabled
      oneshot
    service installd /system/bin/installd //启动安装APK包守护进程
      socket installd stream 600 system system
    service flash_recovery /system/bin/flash_image recovery /system/recovery.img
      oneshot

更多相关文章
·Android进程的生命周期 ·Android常用组件生命周期 ·Android Resources资源 ·Android Data Storage ·Android Content Providers

热门推荐