本文共 7709 字，大约阅读时间需要 25 分钟。

Android Init Language: 来源于system/core/init --------------------- The Android Init Language consists of four broad classes of statements, which are Actions, Commands, Services, and Options. All of these are line-oriented, consisting of tokens separated by whitespace.  The c-style backslash escapes may be used to insert whitespace into a token.  Double quotes may also be used to prevent whitespace from breaking text into multiple tokens.  The backslash, when it is the last character on a line, may be used for line-folding. Lines which start with a # (leading whitespace allowed) are comments. Actions and Services implicitly declare a new section.  All commands or options belong to the section most recently declared.  Commands or options before the first section are ignored. Actions and Services have unique names.  If a second Action or Service is declared with the same name as an existing one, it is ignored as an error.  (??? should we override instead) Actions ------- Actions are named sequences of commands.  Actions have a trigger which is used to determine when the action should occur.  When an event occurs which matches an action's trigger, that action is added to the tail of a to-be-executed queue (unless it is already on the queue). Each action in the queue is dequeued in sequence and each command in that action is executed in sequence.  Init handles other activities (device creation/destruction, property setting, process restarting) "between" the execution of the commands in activities. Actions take the form of: on <trigger>    <command>    <command>    <command> Services -------- Services are programs which init launches and (optionally) restarts when they exit.  Services take the form of: service <name> <pathname> [ <argument> ]*    <option>    <option>    ... Options ------- Options are modifiers to services.  They affect how and when init runs the service. critical    This is a device-critical service. If it exits more than four times in    four minutes, the device will reboot into recovery mode. disabled    This service will not automatically start with its class.    It must be explicitly started by name. setenv <name> <value>    Set the environment variable <name> to <value> in the launched process. socket <name> <type> <perm> [ <user> [ <group> ] ]    Create a unix domain socket named /dev/socket/<name> and pass    its fd to the launched process.  <type> must be "dgram", "stream" or "seqpacket".    User and group default to 0. user <username>    Change to username before exec'ing this service.    Currently defaults to root.  (??? probably should default to nobody)    Currently, if your process requires linux capabilities then you cannot use    this command. You must instead request the capabilities in-process while    still root, and then drop to your desired uid. group <groupname> [ <groupname> ]*    Change to groupname before exec'ing this service.  Additional    groupnames beyond the (required) first one are used to set the    supplemental groups of the process (via setgroups()).    Currently defaults to root.  (??? probably should default to nobody) oneshot    Do not restart the service when it exits. class <name>    Specify a class name for the service.  All services in a    named class may be started or stopped together.  A service    is in the class "default" if one is not specified via the    class option. onrestart     Execute a Command (see below) when service restarts. Triggers --------    Triggers are strings which can be used to match certain kinds    of events and used to cause an action to occur. boot    This is the first trigger that will occur when init starts    (after /init.conf is loaded) <name>=<value>    Triggers of this form occur when the property <name> is set    to the specific value <value>. device-added-<path> device-removed-<path>    Triggers of these forms occur when a device node is added    or removed. service-exited-<name>    Triggers of this form occur when the specified service exits. Commands -------- exec <path> [ <argument> ]*    Fork and execute a program (<path>).  This will block until    the program completes execution.  It is best to avoid exec    as unlike the builtin commands, it runs the risk of getting    init "stuck". (??? maybe there should be a timeout?) export <name> <value>    Set the environment variable <name> equal to <value> in the    global environment (which will be inherited by all processes    started after this command is executed) ifup <interface>    Bring the network interface <interface> online. import <filename>    Parse an init config file, extending the current configuration. hostname <name>    Set the host name. chdir <directory>    Change working directory. chmod <octal-mode> <path>    Change file access permissions. chown <owner> <group> <path>    Change file owner and group. chroot <directory>   Change process root directory. class_start <serviceclass>    Start all services of the specified class if they are    not already running. class_stop <serviceclass>    Stop all services of the specified class if they are    currently running. domainname <name>    Set the domain name. insmod <path>    Install the module at <path> mkdir <path> [mode] [owner] [group]    Create a directory at <path>, optionally with the given mode, owner, and    group. If not provided, the directory is created with permissions 755 and    owned by the root user and root group. mount <type> <device> <dir> [ <mountoption> ]*    Attempt to mount the named device at the directory <dir>    <device> may be of the form mtd@name to specify a mtd block    device by name.    <mountoption>s include "ro", "rw", "remount", "noatime", ... setkey    TBD setprop <name> <value>    Set system property <name> to <value>. setrlimit <resource> <cur> <max>    Set the rlimit for a resource. start <service>    Start a service running if it is not already running. stop <service>    Stop a service from running if it is currently running. symlink <target> <path>    Create a symbolic link at <path> with the value <target> sysclktz <mins_west_of_gmt>    Set the system clock base (0 if system clock ticks in GMT) trigger <event>    Trigger an event.  Used to queue an action from another    action. write <path> <string> [ <string> ]*    Open the file at <path> and write one or more strings    to it with write(2) Properties ---------- Init updates some system properties to provide some insight into what it's doing: init.action    Equal to the name of the action currently being executed or "" if none init.command    Equal to the command being executed or "" if none. init.svc.<name>    State of a named service ("stopped", "running", "restarting") Example init.conf ----------------- # not complete -- just providing some examples of usage # on boot    export PATH /sbin:/system/sbin:/system/bin    export LD_LIBRARY_PATH /system/lib    mkdir /dev    mkdir /proc    mkdir /sys    mount tmpfs tmpfs /dev    mkdir /dev/pts    mkdir /dev/socket    mount devpts devpts /dev/pts    mount proc proc /proc    mount sysfs sysfs /sys    write /proc/cpu/alignment 4    ifup lo    hostname localhost    domainname localhost    mount yaffs2 mtd@system /system    mount yaffs2 mtd@userdata /data    import /system/etc/init.conf    class_start default service adbd /sbin/adbd    user adb    group adb service usbd /system/bin/usbd -r    user usbd    group usbd    socket usbd 666 service zygote /system/bin/app_process -Xzygote /system/bin --zygote    socket zygote 666 service runtime /system/bin/runtime    user system    group system on device-added-/dev/compass    start akmd on device-removed-/dev/compass    stop akmd service akmd /sbin/akmd    disabled    user akmd    group akmd Debugging notes --------------- By default, programs executed by init will drop stdout and stderr into /dev/null. To help with debugging, you can execute your program via the Andoird program logwrapper. This will redirect stdout/stderr into the Android logging system (accessed via logcat). For example service akmd /system/bin/logwrapper /sbin/akmd

转载地址：http://gqfvb.baihongyu.com/