f682b4786a
This isn't particularly useful in and of itself, but it does introduce the first (trivial) unit test, improves the documentation (including details about how to debug init crashes), and made me aware of how unpleasant the existing parser is. I also fixed a bug in passing --- unless you thought the "peboot" and "pm" commands were features... Bug: 19217569 Change-Id: I6ab76129a543ce3ed3dab52ef2c638009874c3de
364 lines
11 KiB
Text
364 lines
11 KiB
Text
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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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One can also test multiple properties to execute a group
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of commands. For example:
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on property:test.a=1 && property:test.b=1
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setprop test.c 1
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The above stub sets test.c to 1 only when
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both test.a=1 and test.b=1
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Commands
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--------
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exec <path> [ <argument> ]*
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This command is not implemented.
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execonce <path> [ <argument> ]*
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Fork and execute a program (<path>). This will block until
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the program completes execution. This command can be run at most
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once during init's lifetime. Subsequent invocations are ignored.
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It is best to avoid exec as unlike the builtin commands, it runs
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the risk of getting init "stuck".
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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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loglevel <level>
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Sets the kernel log level to level. Properties are expanded within <level>.
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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>. Properties are expanded
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within <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> <content>
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Open the file at <path> and write a string to it with write(2).
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If the file does not exist, it will be created. If it does exist,
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it will be truncated. Properties are expanded within <content>.
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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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Android 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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For quicker turnaround when working on init itself, use:
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mm
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m ramdisk-nodeps
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m bootimage-nodeps
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adb reboot bootloader
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fastboot boot $ANDROID_PRODUCT_OUT/boot.img
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Alternatively, use the emulator:
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emulator -partition-size 1024 -verbose -show-kernel -no-window
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You might want to call klog_set_level(6) after the klog_init() call
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so you see the kernel logging in dmesg (or the emulator output).
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