Android 启动过程简析

首先我们先来看android构架图：

android系统是构建在linux系统上面的。

所以android设备启动经历3个过程。

Boot Loader,Linux Kernel & Android 系统服务。

1.基本启动过程

系统引导bootloader 加载boot.img

由bootloader 加载内核kernel

文件系统挂载，init

完成引导进程(文件解析、属性设置、启动服务、执行动作)

重要的服务进程zygote 建立Java Runtime，建立虚拟机 启动Android System Server

系统服务System Server 通过System Manager管理android的服务

桌面launcher 各个服务已经就绪，桌面程序Home在ActivityManagerService的服务过程中建立

2.init

android 启动流程图：

是有kernel启动的第一个进程。

用来完成其他服务的引导进程。

init启动的过程记录在init.rc文件中。

2.1 init.rc的语法

rc文件只有在System/Core/Init/readme.txt中有描述

一共分为4种设计。

Action

Commands

Services

Options

Action & Services 暗示着一个新的语句的开始，这两个关键字后面跟着的 commands 或者 options 都属于这个新语句。

Action就是响应某事件的过程

而services就是可执行程序。

2.2 init.rc实例分析

android5.0下面的init.rc

位置如下：system\core\rootdir

# Copyright (C) 2012 The Android Open Source Project
#
# IMPORTANT: Do not create world writable files or directories.
# This is a common source of Android security bugs.
#

import /init.environ.rc
import /init.usb.rc
import /init.${ro.hardware}.rc
import /init.${ro.zygote}.rc
import /init.trace.rc

on early-init
    # Set init and its forked children's oom_adj.
    write /proc/1/oom_score_adj -1000

    # Apply strict SELinux checking of PROT_EXEC on mmap/mprotect calls.
    write /sys/fs/selinux/checkreqprot 0

    # Set the security context for the init process.
    # This should occur before anything else (e.g. ueventd) is started.
    setcon u:r:init:s0

    # Set the security context of /adb_keys if present.
    restorecon /adb_keys

    start ueventd

    # create mountpoints
    mkdir /mnt 0775 root system

on init
    sysclktz 0

    loglevel 3

    # Backward compatibility
    symlink /system/etc /etc
    symlink /sys/kernel/debug /d

    # Right now vendor lives on the same filesystem as system,
    # but someday that may change.
    symlink /system/vendor /vendor

    # Create cgroup mount point for cpu accounting
    mkdir /acct
    mount cgroup none /acct cpuacct
    mkdir /acct/uid

    # Create cgroup mount point for memory
    mount tmpfs none /sys/fs/cgroup mode=0750,uid=0,gid=1000
    mkdir /sys/fs/cgroup/memory 0750 root system
    mount cgroup none /sys/fs/cgroup/memory memory
    write /sys/fs/cgroup/memory/memory.move_charge_at_immigrate 1
    chown root system /sys/fs/cgroup/memory/tasks
    chmod 0660 /sys/fs/cgroup/memory/tasks
    mkdir /sys/fs/cgroup/memory/sw 0750 root system
    write /sys/fs/cgroup/memory/sw/memory.swappiness 100
    write /sys/fs/cgroup/memory/sw/memory.move_charge_at_immigrate 1
    chown root system /sys/fs/cgroup/memory/sw/tasks
    chmod 0660 /sys/fs/cgroup/memory/sw/tasks

    mkdir /system
    mkdir /data 0771 system system
    mkdir /cache 0770 system cache
    mkdir /config 0500 root root

    # See storage config details at http://source.android.com/tech/storage/
    mkdir /mnt/shell 0700 shell shell
    mkdir /mnt/media_rw 0700 media_rw media_rw
    mkdir /storage 0751 root sdcard_r

    # Directory for putting things only root should see.
    mkdir /mnt/secure 0700 root root

    # Directory for staging bindmounts
    mkdir /mnt/secure/staging 0700 root root

    # Directory-target for where the secure container
    # imagefile directory will be bind-mounted
    mkdir /mnt/secure/asec  0700 root root

    # Secure container public mount points.
    mkdir /mnt/asec  0700 root system
    mount tmpfs tmpfs /mnt/asec mode=0755,gid=1000

    # Filesystem image public mount points.
    mkdir /mnt/obb 0700 root system
    mount tmpfs tmpfs /mnt/obb mode=0755,gid=1000

    # memory control cgroup
    mkdir /dev/memcg 0700 root system
    mount cgroup none /dev/memcg memory

    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
    write /proc/sys/kernel/sched_compat_yield 1
    write /proc/sys/kernel/sched_child_runs_first 0
    write /proc/sys/kernel/randomize_va_space 2
    write /proc/sys/kernel/kptr_restrict 2
    write /proc/sys/vm/mmap_min_addr 32768
    write /proc/sys/net/ipv4/ping_group_range "0 2147483647"
    write /proc/sys/net/unix/max_dgram_qlen 300
    write /proc/sys/kernel/sched_rt_runtime_us 950000
    write /proc/sys/kernel/sched_rt_period_us 1000000

    # reflect fwmark from incoming packets onto generated replies
    write /proc/sys/net/ipv4/fwmark_reflect 1
    write /proc/sys/net/ipv6/fwmark_reflect 1

    # set fwmark on accepted sockets
    write /proc/sys/net/ipv4/tcp_fwmark_accept 1

    # Create cgroup mount points for process groups
    mkdir /dev/cpuctl
    mount cgroup none /dev/cpuctl cpu
    chown system system /dev/cpuctl
    chown system system /dev/cpuctl/tasks
    chmod 0660 /dev/cpuctl/tasks
    write /dev/cpuctl/cpu.shares 1024
    write /dev/cpuctl/cpu.rt_runtime_us 950000
    write /dev/cpuctl/cpu.rt_period_us 1000000

    mkdir /dev/cpuctl/apps
    chown system system /dev/cpuctl/apps/tasks
    chmod 0666 /dev/cpuctl/apps/tasks
    write /dev/cpuctl/apps/cpu.shares 1024
    write /dev/cpuctl/apps/cpu.rt_runtime_us 800000
    write /dev/cpuctl/apps/cpu.rt_period_us 1000000

    mkdir /dev/cpuctl/apps/bg_non_interactive
    chown system system /dev/cpuctl/apps/bg_non_interactive/tasks
    chmod 0666 /dev/cpuctl/apps/bg_non_interactive/tasks
    # 5.0 %
    write /dev/cpuctl/apps/bg_non_interactive/cpu.shares 52
    write /dev/cpuctl/apps/bg_non_interactive/cpu.rt_runtime_us 700000
    write /dev/cpuctl/apps/bg_non_interactive/cpu.rt_period_us 1000000

    # qtaguid will limit access to specific data based on group memberships.
    #   net_bw_acct grants impersonation of socket owners.
    #   net_bw_stats grants access to other apps' detailed tagged-socket stats.
    chown root net_bw_acct /proc/net/xt_qtaguid/ctrl
    chown root net_bw_stats /proc/net/xt_qtaguid/stats

    # Allow everybody to read the xt_qtaguid resource tracking misc dev.
    # This is needed by any process that uses socket tagging.
    chmod 0644 /dev/xt_qtaguid

    # Create location for fs_mgr to store abbreviated output from filesystem
    # checker programs.
    mkdir /dev/fscklogs 0770 root system

    # pstore/ramoops previous console log
    mount pstore pstore /sys/fs/pstore
    chown system log /sys/fs/pstore/console-ramoops
    chmod 0440 /sys/fs/pstore/console-ramoops

# Healthd can trigger a full boot from charger mode by signaling this
# property when the power button is held.
on property:sys.boot_from_charger_mode=1
    class_stop charger
    trigger late-init

# Load properties from /system/ + /factory after fs mount.
on load_all_props_action
    load_all_props

# Indicate to fw loaders that the relevant mounts are up.
on firmware_mounts_complete
    rm /dev/.booting

# Mount filesystems and start core system services.
on late-init
    trigger early-fs
    trigger fs
    trigger post-fs
    trigger post-fs-data

    # Load properties from /system/ + /factory after fs mount. Place
    # this in another action so that the load will be scheduled after the prior
    # issued fs triggers have completed.
    trigger load_all_props_action

    # Remove a file to wake up anything waiting for firmware.
    trigger firmware_mounts_complete

    trigger early-boot
    trigger boot

on post-fs
    # once everything is setup, no need to modify /
    mount rootfs rootfs / ro remount
    # mount shared so changes propagate into child namespaces
    mount rootfs rootfs / shared rec

    # We chown/chmod /cache again so because mount is run as root + defaults
    chown system cache /cache
    chmod 0770 /cache
    # We restorecon /cache in case the cache partition has been reset.
    restorecon_recursive /cache

    # This may have been created by the recovery system with odd permissions
    chown system cache /cache/recovery
    chmod 0770 /cache/recovery

    #change permissions on vmallocinfo so we can grab it from bugreports
    chown root log /proc/vmallocinfo
    chmod 0440 /proc/vmallocinfo

    chown root log /proc/slabinfo
    chmod 0440 /proc/slabinfo

    #change permissions on kmsg & sysrq-trigger so bugreports can grab kthread stacks
    chown root system /proc/kmsg
    chmod 0440 /proc/kmsg
    chown root system /proc/sysrq-trigger
    chmod 0220 /proc/sysrq-trigger
    chown system log /proc/last_kmsg
    chmod 0440 /proc/last_kmsg

    # make the selinux kernel policy world-readable
    chmod 0444 /sys/fs/selinux/policy

    # create the lost+found directories, so as to enforce our permissions
    mkdir /cache/lost+found 0770 root root

on post-fs-data
    # We chown/chmod /data again so because mount is run as root + defaults
    chown system system /data
    chmod 0771 /data
    # We restorecon /data in case the userdata partition has been reset.
    restorecon /data

    # Avoid predictable entropy pool. Carry over entropy from previous boot.
    copy /data/system/entropy.dat /dev/urandom

    # Create dump dir and collect dumps.
    # Do this before we mount cache so eventually we can use cache for
    # storing dumps on platforms which do not have a dedicated dump partition.
    mkdir /data/dontpanic 0750 root log

    # Collect apanic data, free resources and re-arm trigger
    copy /proc/apanic_console /data/dontpanic/apanic_console
    chown root log /data/dontpanic/apanic_console
    chmod 0640 /data/dontpanic/apanic_console

    copy /proc/apanic_threads /data/dontpanic/apanic_threads
    chown root log /data/dontpanic/apanic_threads
    chmod 0640 /data/dontpanic/apanic_threads

    write /proc/apanic_console 1

    # create basic filesystem structure
    mkdir /data/misc 01771 system misc
    mkdir /data/misc/adb 02750 system shell
    mkdir /data/misc/bluedroid 0770 bluetooth net_bt_stack
    mkdir /data/misc/bluetooth 0770 system system
    mkdir /data/misc/keystore 0700 keystore keystore
    mkdir /data/misc/keychain 0771 system system
    mkdir /data/misc/net 0750 root shell
    mkdir /data/misc/radio 0770 system radio
    mkdir /data/misc/sms 0770 system radio
    mkdir /data/misc/zoneinfo 0775 system system
    mkdir /data/misc/vpn 0770 system vpn
    mkdir /data/misc/shared_relro 0771 shared_relro shared_relro
    mkdir /data/misc/systemkeys 0700 system system
    mkdir /data/misc/wifi 0770 wifi wifi
    mkdir /data/misc/wifi/sockets 0770 wifi wifi
    mkdir /data/misc/wifi/wpa_supplicant 0770 wifi wifi
    mkdir /data/misc/ethernet 0770 system system
    mkdir /data/misc/dhcp 0770 dhcp dhcp
    mkdir /data/misc/user 0771 root root
    # give system access to wpa_supplicant.conf for backup and restore
    chmod 0660 /data/misc/wifi/wpa_supplicant.conf
    mkdir /data/local 0751 root root
    mkdir /data/misc/media 0700 media media

    # For security reasons, /data/local/tmp should always be empty.
    # Do not place files or directories in /data/local/tmp
    mkdir /data/local/tmp 0771 shell shell
    mkdir /data/data 0771 system system
    mkdir /data/app-private 0771 system system
    mkdir /data/app-asec 0700 root root
    mkdir /data/app-lib 0771 system system
    mkdir /data/app 0771 system system
    mkdir /data/property 0700 root root

    # create dalvik-cache, so as to enforce our permissions
    mkdir /data/dalvik-cache 0771 root root
    mkdir /data/dalvik-cache/profiles 0711 system system

    # create resource-cache and double-check the perms
    mkdir /data/resource-cache 0771 system system
    chown system system /data/resource-cache
    chmod 0771 /data/resource-cache

    # create the lost+found directories, so as to enforce our permissions
    mkdir /data/lost+found 0770 root root

    # create directory for DRM plug-ins - give drm the read/write access to
    # the following directory.
    mkdir /data/drm 0770 drm drm

    # create directory for MediaDrm plug-ins - give drm the read/write access to
    # the following directory.
    mkdir /data/mediadrm 0770 mediadrm mediadrm

    # symlink to bugreport storage location
    symlink /data/data/com.android.shell/files/bugreports /data/bugreports

    # Separate location for storing security policy files on data
    mkdir /data/security 0711 system system

    # Reload policy from /data/security if present.
    setprop selinux.reload_policy 1

    # Set SELinux security contexts on upgrade or policy update.
    restorecon_recursive /data

    # If there is no fs-post-data action in the init.<device>.rc file, you
    # must uncomment this line, otherwise encrypted filesystems
    # won't work.
    # Set indication (checked by vold) that we have finished this action
    #setprop vold.post_fs_data_done 1

on boot
    # basic network init
    ifup lo
    hostname localhost
    domainname localdomain

    # set RLIMIT_NICE to allow priorities from 19 to -20
    setrlimit 13 40 40

    # Memory management.  Basic kernel parameters, and allow the high
    # level system server to be able to adjust the kernel OOM driver
    # parameters to match how it is managing things.
    write /proc/sys/vm/overcommit_memory 1
    write /proc/sys/vm/min_free_order_shift 4
    chown root system /sys/module/lowmemorykiller/parameters/adj
    chmod 0220 /sys/module/lowmemorykiller/parameters/adj
    chown root system /sys/module/lowmemorykiller/parameters/minfree
    chmod 0220 /sys/module/lowmemorykiller/parameters/minfree

    # Tweak background writeout
    write /proc/sys/vm/dirty_expire_centisecs 200
    write /proc/sys/vm/dirty_background_ratio  5

    # Permissions for System Server and daemons.
    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 system system /sys/power/autosleep
    chown system system /sys/power/state
    chown system system /sys/power/wakeup_count
    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/devices/system/cpu/cpufreq/interactive/timer_rate
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/timer_rate
    chown system system /sys/devices/system/cpu/cpufreq/interactive/timer_slack
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/timer_slack
    chown system system /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
    chown system system /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
    chown system system /sys/devices/system/cpu/cpufreq/interactive/target_loads
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/target_loads
    chown system system /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
    chown system system /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
    chown system system /sys/devices/system/cpu/cpufreq/interactive/boost
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/boost
    chown system system /sys/devices/system/cpu/cpufreq/interactive/boostpulse
    chown system system /sys/devices/system/cpu/cpufreq/interactive/input_boost
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/input_boost
    chown system system /sys/devices/system/cpu/cpufreq/interactive/boostpulse_duration
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/boostpulse_duration
    chown system system /sys/devices/system/cpu/cpufreq/interactive/io_is_busy
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/io_is_busy

    # Assume SMP uses shared cpufreq policy for all CPUs
    chown system system /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    chmod 0660 /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq

    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/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

    # Define default initial receive window size in segments.
    setprop net.tcp.default_init_rwnd 60

    class_start core

on nonencrypted
    class_start main
    class_start late_start

on property:vold.decrypt=trigger_default_encryption
    start defaultcrypto

on property:vold.decrypt=trigger_encryption
    start surfaceflinger
    start encrypt

on property:sys.init_log_level=*
    loglevel ${sys.init_log_level}

on charger
    class_start charger

on property:vold.decrypt=trigger_reset_main
    class_reset main

on property:vold.decrypt=trigger_load_persist_props
    load_persist_props

on property:vold.decrypt=trigger_post_fs_data
    trigger post-fs-data

on property:vold.decrypt=trigger_restart_min_framework
    class_start main

on property:vold.decrypt=trigger_restart_framework
    class_start main
    class_start late_start

on property:vold.decrypt=trigger_shutdown_framework
    class_reset late_start
    class_reset main

on property:sys.powerctl=*
    powerctl ${sys.powerctl}

# system server cannot write to /proc/sys files,
# and chown/chmod does not work for /proc/sys/ entries.
# So proxy writes through init.
on property:sys.sysctl.extra_free_kbytes=*
    write /proc/sys/vm/extra_free_kbytes ${sys.sysctl.extra_free_kbytes}

# "tcp_default_init_rwnd" Is too long!
on property:sys.sysctl.tcp_def_init_rwnd=*
    write /proc/sys/net/ipv4/tcp_default_init_rwnd ${sys.sysctl.tcp_def_init_rwnd}

## Daemon processes to be run by init.
##
service ueventd /sbin/ueventd
    class core
    critical
    seclabel u:r:ueventd:s0

service logd /system/bin/logd
    class core
    socket logd stream 0666 logd logd
    socket logdr seqpacket 0666 logd logd
    socket logdw dgram 0222 logd logd
    seclabel u:r:logd:s0

service healthd /sbin/healthd
    class core
    critical
    seclabel u:r:healthd:s0

service console /system/bin/sh
    class core
    console
    disabled
    user shell
    group shell log
    seclabel u:r:shell:s0

on property:ro.debuggable=1
    start console

# adbd is controlled via property triggers in init.<platform>.usb.rc
service adbd /sbin/adbd --root_seclabel=u:r:su:s0
    class core
    socket adbd stream 660 system system
    disabled
    seclabel u:r:adbd:s0

# adbd on at boot in emulator
on property:ro.kernel.qemu=1
    start adbd

service lmkd /system/bin/lmkd
    class core
    critical
    socket lmkd seqpacket 0660 system system

service servicemanager /system/bin/servicemanager
    class core
    user system
    group system
    critical
    onrestart restart healthd
    onrestart restart zygote
    onrestart restart media
    onrestart restart surfaceflinger
    onrestart restart drm

service vold /system/bin/vold
    class core
    socket vold stream 0660 root mount
    ioprio be 2

service netd /system/bin/netd
    class main
    socket netd stream 0660 root system
    socket dnsproxyd stream 0660 root inet
    socket mdns stream 0660 root system
    socket fwmarkd stream 0660 root inet

service debuggerd /system/bin/debuggerd
    class main

service debuggerd64 /system/bin/debuggerd64
    class main

service ril-daemon /system/bin/rild
    class main
    socket rild stream 660 root radio
    socket rild-debug stream 660 radio system
    user root
    group radio cache inet misc audio log

service surfaceflinger /system/bin/surfaceflinger
    class core
    user system
    group graphics drmrpc
    onrestart restart zygote

service drm /system/bin/drmserver
    class main
    user drm
    group drm system inet drmrpc

service media /system/bin/mediaserver
    class main
    user media
    group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
    ioprio rt 4

# One shot invocation to deal with encrypted volume.
service defaultcrypto /system/bin/vdc --wait cryptfs mountdefaultencrypted
    disabled
    oneshot
    # vold will set vold.decrypt to trigger_restart_framework (default
    # encryption) or trigger_restart_min_framework (other encryption)

# One shot invocation to encrypt unencrypted volumes
service encrypt /system/bin/vdc --wait cryptfs enablecrypto inplace default
    disabled
    oneshot
    # vold will set vold.decrypt to trigger_restart_framework (default
    # encryption)

service bootanim /system/bin/bootanimation
    class core
    user graphics
    group graphics audio
    disabled
    oneshot

service installd /system/bin/installd
    class main
    socket installd stream 600 system system

service flash_recovery /system/bin/install-recovery.sh
    class main
    seclabel u:r:install_recovery:s0
    oneshot

service racoon /system/bin/racoon
    class main
    socket racoon stream 600 system system
    # IKE uses UDP port 500. Racoon will setuid to vpn after binding the port.
    group vpn net_admin inet
    disabled
    oneshot

service mtpd /system/bin/mtpd
    class main
    socket mtpd stream 600 system system
    user vpn
    group vpn net_admin inet net_raw
    disabled
    oneshot

service keystore /system/bin/keystore /data/misc/keystore
    class main
    user keystore
    group keystore drmrpc

service dumpstate /system/bin/dumpstate -s
    class main
    socket dumpstate stream 0660 shell log
    disabled
    oneshot

service mdnsd /system/bin/mdnsd
    class main
    user mdnsr
    group inet net_raw
    socket mdnsd stream 0660 mdnsr inet
    disabled
    oneshot

service pre-recovery /system/bin/uncrypt
    class main
    disabled
    oneshot

inti.rc

节选部分关键代码：

on init
    sysclktz 0    //设置基准时间，默认是0

    loglevel 3

    # Backward compatibility
    symlink /system/etc /etc            //设置链接文件
    symlink /sys/kernel/debug /d     //设置链接文件

    # Right now vendor lives on the same filesystem as system,
    # but someday that may change.
    symlink /system/vendor /vendor

    # Create cgroup mount point for cpu accounting
    mkdir /acct                            //创建acct文件夹
    mount cgroup none /acct cpuacct
    mkdir /acct/uid

    # Create cgroup mount point for memory
    mount tmpfs none /sys/fs/cgroup mode=0750,uid=0,gid=1000
    mkdir /sys/fs/cgroup/memory 0750 root system
    mount cgroup none /sys/fs/cgroup/memory memory
    write /sys/fs/cgroup/memory/memory.move_charge_at_immigrate 1
    chown root system /sys/fs/cgroup/memory/tasks
    chmod 0660 /sys/fs/cgroup/memory/tasks
    mkdir /sys/fs/cgroup/memory/sw 0750 root system
    write /sys/fs/cgroup/memory/sw/memory.swappiness 100
    write /sys/fs/cgroup/memory/sw/memory.move_charge_at_immigrate 1
    chown root system /sys/fs/cgroup/memory/sw/tasks
    chmod 0660 /sys/fs/cgroup/memory/sw/tasks

    mkdir /system
    mkdir /data 0771 system system
    mkdir /cache 0770 system cache
    mkdir /config 0500 root root    

如上所示，主要是创建文件夹，链接文件，挂载等等的操作。

on boot
    # basic network init
    ifup lo
    hostname localhost
    domainname localdomain

    # set RLIMIT_NICE to allow priorities from 19 to -20
    setrlimit 13 40 40

    # Memory management.  Basic kernel parameters, and allow the high
    # level system server to be able to adjust the kernel OOM driver
    # parameters to match how it is managing things.
    write /proc/sys/vm/overcommit_memory 1
    write /proc/sys/vm/min_free_order_shift 4
    chown root system /sys/module/lowmemorykiller/parameters/adj
    chmod 0220 /sys/module/lowmemorykiller/parameters/adj
    chown root system /sys/module/lowmemorykiller/parameters/minfree
    chmod 0220 /sys/module/lowmemorykiller/parameters/minfree

    # Tweak background writeout
    write /proc/sys/vm/dirty_expire_centisecs 200
    write /proc/sys/vm/dirty_background_ratio  5

    # Permissions for System Server and daemons.
    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 system system /sys/power/autosleep
    chown system system /sys/power/state
    chown system system /sys/power/wakeup_count
    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

都是设置权限的操作。

service servicemanager /system/bin/servicemanager
    class core
    user system
    group system
    critical
    onrestart restart healthd
    onrestart restart zygote
    onrestart restart media
    onrestart restart surfaceflinger
    onrestart restart drm

启动servicemanager这个大管家。

其他还有很多，具体看init.rc文件。

3.系统关键服务启动简析

3.1 servicemanager---大管家

如上，servicemanager的启动，会同时restart其他一些关键的进程。

core的特性表示其他同类型的class。会同时启动或者关闭。

service ueventd /sbin/ueventd
    class core
    critical
    seclabel u:r:ueventd:s0

service logd /system/bin/logd
    class core
    socket logd stream 0666 logd logd
    socket logdr seqpacket 0666 logd logd
    socket logdw dgram 0222 logd logd
    seclabel u:r:logd:s0

service healthd /sbin/healthd
    class core
    critical
    seclabel u:r:healthd:s0

service console /system/bin/sh
    class core
    console
    disabled
    user shell
    group shell log
    seclabel u:r:shell:s0

critical意味着，这个是关键进程，一旦进程在4分钟内退出了4次，手机将会进入还原模式。

3.2 Zygote

android中绝大部分进程都是从zygote中来的。

zygote的启动在android5.0的时候，可以进行配置。

service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd

我们选择一个看看：

从上面可以看出：

ServiceName：zygote

path：/system/bin/app_process64

启动的位置在app_process64 并且之后启动systemserver。

先看看app_process64是什么鬼？

源码在：frameworks\base\cmds\app_process\app_main.cpp

int main(int argc, char* const argv[])
{
    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) {
        // Older kernels don't understand PR_SET_NO_NEW_PRIVS and return
        // EINVAL. Don't die on such kernels.
        if (errno != EINVAL) {
            LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno));
            return 12;
        }
    }

    AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
    // Process command line arguments
    // ignore argv[0]
    argc--;
    argv++;

    // Everything up to '--' or first non '-' arg goes to the vm.
    //
    // The first argument after the VM args is the "parent dir", which
    // is currently unused.
    //
    // After the parent dir, we expect one or more the following internal
    // arguments :
    //
    // --zygote : Start in zygote mode
    // --start-system-server : Start the system server.
    // --application : Start in application (stand alone, non zygote) mode.
    // --nice-name : The nice name for this process.
    //
    // For non zygote starts, these arguments will be followed by
    // the main class name. All remaining arguments are passed to
    // the main method of this class.
    //
    // For zygote starts, all remaining arguments are passed to the zygote.
    // main function.
    //
    // Note that we must copy argument string values since we will rewrite the
    // entire argument block when we apply the nice name to argv0.

    int i;
    for (i = 0; i < argc; i++) {
        if (argv[i][0] != '-') {
            break;
        }
        if (argv[i][1] == '-' && argv[i][2] == 0) {
            ++i; // Skip --.
            break;
        }
        runtime.addOption(strdup(argv[i]));
    }

    // Parse runtime arguments.  Stop at first unrecognized option.
    bool zygote = false;
    bool startSystemServer = false;
    bool application = false;
    String8 niceName;
    String8 className;

    ++i;  // Skip unused "parent dir" argument.
    while (i < argc) {
        const char* arg = argv[i++];
        if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;
        } else if (strcmp(arg, "--start-system-server") == 0) {
            startSystemServer = true;
        } else if (strcmp(arg, "--application") == 0) {
            application = true;
        } else if (strncmp(arg, "--nice-name=", 12) == 0) {
            niceName.setTo(arg + 12);
        } else if (strncmp(arg, "--", 2) != 0) {
            className.setTo(arg);
            break;
        } else {
            --i;
            break;
        }
    }

    Vector<String8> args;
    if (!className.isEmpty()) {
        // We're not in zygote mode, the only argument we need to pass
        // to RuntimeInit is the application argument.
        //
        // The Remainder of args get passed to startup class main(). Make
        // copies of them before we overwrite them with the process name.
        args.add(application ? String8("application") : String8("tool"));
        runtime.setClassNameAndArgs(className, argc - i, argv + i);
    } else {
        // We're in zygote mode.
        maybeCreateDalvikCache();

        if (startSystemServer) {
            args.add(String8("start-system-server"));
        }

        char prop[PROP_VALUE_MAX];
        if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
            LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
                ABI_LIST_PROPERTY);
            return 11;
        }

        String8 abiFlag("--abi-list=");
        abiFlag.append(prop);
        args.add(abiFlag);

        // In zygote mode, pass all remaining arguments to the zygote
        // main() method.
        for (; i < argc; ++i) {
            args.add(String8(argv[i]));
        }
    }

    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string());
        set_process_name(niceName.string());
    }

    if (zygote) {
        runtime.start("com.android.internal.os.ZygoteInit", args);
    } else if (className) {
        runtime.start("com.android.internal.os.RuntimeInit", args);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
        return 10;
    }
}

main

关键代码是

if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;

如果是zygote，就启动它：

runtime.start("com.android.internal.os.ZygoteInit", args);

3.3 systemserver

systemservice中的main，然后启动run：

        // Start services.
        try {
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
        } catch (Throwable ex) {
            Slog.e("System", "******************************************");
            Slog.e("System", "************ Failure starting system services", ex);
            throw ex;
        }

在startBootstrapServices中启动，

AMS，PMS等服务

startOtherServices中启动

启动了WMS，

是的，android最重要的2个系统服务，启动了。