333 lines
9.7 KiB
Plaintext
333 lines
9.7 KiB
Plaintext
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Android Init Language
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---------------------
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The Android Init Language consists of four broad classes of statements,
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which are Actions, Commands, Services, and Options.
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All of these are line-oriented, consisting of tokens separated by
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whitespace. The c-style backslash escapes may be used to insert
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whitespace into a token. Double quotes may also be used to prevent
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whitespace from breaking text into multiple tokens. The backslash,
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when it is the last character on a line, may be used for line-folding.
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Lines which start with a # (leading whitespace allowed) are comments.
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Actions and Services implicitly declare a new section. All commands
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or options belong to the section most recently declared. Commands
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or options before the first section are ignored.
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Actions and Services have unique names. If a second Action or Service
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is declared with the same name as an existing one, it is ignored as
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an error. (??? should we override instead)
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Actions
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-------
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Actions are named sequences of commands. Actions have a trigger which
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is used to determine when the action should occur. When an event
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occurs which matches an action's trigger, that action is added to
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the tail of a to-be-executed queue (unless it is already on the
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queue).
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Each action in the queue is dequeued in sequence and each command in
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that action is executed in sequence. Init handles other activities
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(device creation/destruction, property setting, process restarting)
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"between" the execution of the commands in activities.
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Actions take the form of:
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on <trigger>
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<command>
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<command>
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<command>
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Services
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--------
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Services are programs which init launches and (optionally) restarts
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when they exit. Services take the form of:
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service <name> <pathname> [ <argument> ]*
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<option>
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<option>
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...
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Options
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-------
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Options are modifiers to services. They affect how and when init
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runs the service.
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critical
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This is a device-critical service. If it exits more than four times in
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four minutes, the device will reboot into recovery mode.
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disabled
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This service will not automatically start with its class.
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It must be explicitly started by name.
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setenv <name> <value>
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Set the environment variable <name> to <value> in the launched process.
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socket <name> <type> <perm> [ <user> [ <group> [ <context> ] ] ]
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Create a unix domain socket named /dev/socket/<name> and pass
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its fd to the launched process. <type> must be "dgram", "stream" or "seqpacket".
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User and group default to 0.
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Context is the SELinux security context for the socket.
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It defaults to the service security context, as specified by seclabel or
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computed based on the service executable file security context.
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user <username>
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Change to username before exec'ing this service.
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Currently defaults to root. (??? probably should default to nobody)
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Currently, if your process requires linux capabilities then you cannot use
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this command. You must instead request the capabilities in-process while
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still root, and then drop to your desired uid.
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group <groupname> [ <groupname> ]*
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Change to groupname before exec'ing this service. Additional
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groupnames beyond the (required) first one are used to set the
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supplemental groups of the process (via setgroups()).
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Currently defaults to root. (??? probably should default to nobody)
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seclabel <securitycontext>
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Change to securitycontext before exec'ing this service.
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Primarily for use by services run from the rootfs, e.g. ueventd, adbd.
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Services on the system partition can instead use policy-defined transitions
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based on their file security context.
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If not specified and no transition is defined in policy, defaults to the init context.
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oneshot
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Do not restart the service when it exits.
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class <name>
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Specify a class name for the service. All services in a
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named class may be started or stopped together. A service
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is in the class "default" if one is not specified via the
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class option.
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onrestart
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Execute a Command (see below) when service restarts.
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Triggers
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--------
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Triggers are strings which can be used to match certain kinds
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of events and used to cause an action to occur.
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boot
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This is the first trigger that will occur when init starts
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(after /init.conf is loaded)
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<name>=<value>
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Triggers of this form occur when the property <name> is set
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to the specific value <value>.
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Commands
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--------
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exec <path> [ <argument> ]*
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Fork and execute a program (<path>). This will block until
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the program completes execution. It is best to avoid exec
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as unlike the builtin commands, it runs the risk of getting
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init "stuck". (??? maybe there should be a timeout?)
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export <name> <value>
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Set the environment variable <name> equal to <value> in the
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global environment (which will be inherited by all processes
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started after this command is executed)
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ifup <interface>
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Bring the network interface <interface> online.
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import <filename>
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Parse an init config file, extending the current configuration.
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hostname <name>
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Set the host name.
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chdir <directory>
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Change working directory.
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chmod <octal-mode> <path>
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Change file access permissions.
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chown <owner> <group> <path>
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Change file owner and group.
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chroot <directory>
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Change process root directory.
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class_start <serviceclass>
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Start all services of the specified class if they are
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not already running.
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class_stop <serviceclass>
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Stop all services of the specified class if they are
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currently running.
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domainname <name>
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Set the domain name.
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enable <servicename>
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Turns a disabled service into an enabled one as if the service did not
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specify disabled.
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If the service is supposed to be running, it will be started now.
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Typically used when the bootloader sets a variable that indicates a specific
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service should be started when needed. E.g.
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on property:ro.boot.myfancyhardware=1
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enable my_fancy_service_for_my_fancy_hardware
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insmod <path>
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Install the module at <path>
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mkdir <path> [mode] [owner] [group]
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Create a directory at <path>, optionally with the given mode, owner, and
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group. If not provided, the directory is created with permissions 755 and
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owned by the root user and root group.
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mount <type> <device> <dir> [ <mountoption> ]*
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Attempt to mount the named device at the directory <dir>
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<device> may be of the form mtd@name to specify a mtd block
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device by name.
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<mountoption>s include "ro", "rw", "remount", "noatime", ...
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restorecon <path> [ <path> ]*
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Restore the file named by <path> to the security context specified
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in the file_contexts configuration.
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Not required for directories created by the init.rc as these are
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automatically labeled correctly by init.
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restorecon_recursive <path> [ <path> ]*
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Recursively restore the directory tree named by <path> to the
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security contexts specified in the file_contexts configuration.
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setcon <securitycontext>
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Set the current process security context to the specified string.
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This is typically only used from early-init to set the init context
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before any other process is started.
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setenforce 0|1
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Set the SELinux system-wide enforcing status.
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0 is permissive (i.e. log but do not deny), 1 is enforcing.
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setkey
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TBD
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setprop <name> <value>
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Set system property <name> to <value>.
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setrlimit <resource> <cur> <max>
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Set the rlimit for a resource.
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setsebool <name> <value>
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Set SELinux boolean <name> to <value>.
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<value> may be 1|true|on or 0|false|off
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start <service>
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Start a service running if it is not already running.
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stop <service>
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Stop a service from running if it is currently running.
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symlink <target> <path>
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Create a symbolic link at <path> with the value <target>
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sysclktz <mins_west_of_gmt>
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Set the system clock base (0 if system clock ticks in GMT)
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trigger <event>
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Trigger an event. Used to queue an action from another
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action.
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wait <path> [ <timeout> ]
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Poll for the existence of the given file and return when found,
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or the timeout has been reached. If timeout is not specified it
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currently defaults to five seconds.
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write <path> <string>
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Open the file at <path> and write a string to it with write(2)
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without appending.
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Properties
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----------
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Init updates some system properties to provide some insight into
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what it's doing:
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init.action
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Equal to the name of the action currently being executed or "" if none
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init.command
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Equal to the command being executed or "" if none.
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init.svc.<name>
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State of a named service ("stopped", "running", "restarting")
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Example init.conf
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-----------------
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# not complete -- just providing some examples of usage
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#
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on boot
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export PATH /sbin:/system/sbin:/system/bin
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export LD_LIBRARY_PATH /system/lib
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mkdir /dev
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mkdir /proc
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mkdir /sys
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mount tmpfs tmpfs /dev
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mkdir /dev/pts
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mkdir /dev/socket
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mount devpts devpts /dev/pts
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mount proc proc /proc
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mount sysfs sysfs /sys
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write /proc/cpu/alignment 4
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ifup lo
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hostname localhost
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domainname localhost
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mount yaffs2 mtd@system /system
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mount yaffs2 mtd@userdata /data
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import /system/etc/init.conf
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class_start default
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service adbd /sbin/adbd
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user adb
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group adb
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service usbd /system/bin/usbd -r
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user usbd
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group usbd
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socket usbd 666
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service zygote /system/bin/app_process -Xzygote /system/bin --zygote
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socket zygote 666
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service runtime /system/bin/runtime
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user system
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group system
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service akmd /sbin/akmd
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disabled
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user akmd
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group akmd
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Debugging notes
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---------------
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By default, programs executed by init will drop stdout and stderr into
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/dev/null. To help with debugging, you can execute your program via the
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Andoird program logwrapper. This will redirect stdout/stderr into the
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Android logging system (accessed via logcat).
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For example
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service akmd /system/bin/logwrapper /sbin/akmd
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