401 lines
13 KiB
Plaintext
401 lines
13 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> [ <seclabel> ] ] ]
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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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'seclabel' 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 <seclabel>
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Change to 'seclabel' 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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writepid <file...>
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Write the child's pid to the given files when it forks. Meant for
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cgroup/cpuset usage.
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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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bootchart_init
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Start bootcharting if configured (see below).
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This is included in the default init.rc.
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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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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 and disable all services of the specified class if they are
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currently running.
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class_reset <serviceclass>
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Stop all services of the specified class if they are
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currently running, without disabling them. They can be restarted
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later using class_start.
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copy <src> <dst>
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Copies a file. Similar to write, but useful for binary/large
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amounts of data.
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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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exec [ <seclabel> [ <user> [ <group> ]* ] ] -- <command> [ <argument> ]*
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Fork and execute command with the given arguments. The command starts
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after "--" so that an optional security context, user, and supplementary
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groups can be provided. No other commands will be run until this one
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finishes. <seclabel> can be a - to denote default.
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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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hostname <name>
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Set the host name.
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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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insmod <path>
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Install the module at <path>
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load_all_props
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Loads properties from /system, /vendor, et cetera.
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This is included in the default init.rc.
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load_persist_props
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Loads persistent properties when /data has been decrypted.
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This is included in the default init.rc.
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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. If provided, the mode, owner and group
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will be updated if the directory exists already.
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mount_all <fstab>
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Calls fs_mgr_mount_all on the given fs_mgr-format fstab.
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mount <type> <device> <dir> [ <flag> ]* [<options>]
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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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<flag>s include "ro", "rw", "remount", "noatime", ...
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<options> include "barrier=1", "noauto_da_alloc", "discard", ... as
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a comma separated string, eg: barrier=1,noauto_da_alloc
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powerctl
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Internal implementation detail used to respond to changes to the
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"sys.powerctl" system property, used to implement rebooting.
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restart <service>
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Like stop, but doesn't disable the service.
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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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rm <path>
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Calls unlink(2) on the given path. You might want to
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use "exec -- rm ..." instead (provided the system partition is
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already mounted).
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rmdir <path>
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Calls rmdir(2) on the given path.
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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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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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swapon_all <fstab>
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Calls fs_mgr_swapon_all on the given fstab file.
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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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verity_load_state
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Internal implementation detail used to load dm-verity state.
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verity_update_state <mount_point>
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Internal implementation detail used to update dm-verity state and
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set the partition.<mount_point>.verified properties used by adb remount
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because fs_mgr can't set them directly itself.
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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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Bootcharting
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------------
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This version of init contains code to perform "bootcharting": generating log
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files that can be later processed by the tools provided by www.bootchart.org.
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On the emulator, use the -bootchart <timeout> option to boot with bootcharting
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activated for <timeout> seconds.
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On a device, create /data/bootchart/start with a command like the following:
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adb shell 'echo $TIMEOUT > /data/bootchart/start'
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Where the value of $TIMEOUT corresponds to the desired bootcharted period in
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seconds. Bootcharting will stop after that many seconds have elapsed.
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You can also stop the bootcharting at any moment by doing the following:
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adb shell 'echo 1 > /data/bootchart/stop'
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Note that /data/bootchart/stop is deleted automatically by init at the end of
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the bootcharting. This is not the case with /data/bootchart/start, so don't
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forget to delete it when you're done collecting data.
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The log files are written to /data/bootchart/. A script is provided to
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retrieve them and create a bootchart.tgz file that can be used with the
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bootchart command-line utility:
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sudo apt-get install pybootchartgui
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# grab-bootchart.sh uses $ANDROID_SERIAL.
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$ANDROID_BUILD_TOP/system/core/init/grab-bootchart.sh
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One thing to watch for is that the bootchart will show init as if it started
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running at 0s. You'll have to look at dmesg to work out when the kernel
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actually started init.
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Comparing two bootcharts
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------------------------
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A handy script named compare-bootcharts.py can be used to compare the
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start/end time of selected processes. The aforementioned grab-bootchart.sh
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will leave a bootchart tarball named bootchart.tgz at /tmp/android-bootchart.
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If two such barballs are preserved on the host machine under different
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directories, the script can list the timestamps differences. For example:
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Usage: system/core/init/compare-bootcharts.py base_bootchart_dir
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exp_bootchart_dir
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process: baseline experiment (delta)
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- Unit is ms (a jiffy is 10 ms on the system)
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------------------------------------
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/init: 50 40 (-10)
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/system/bin/surfaceflinger: 4320 4470 (+150)
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/system/bin/bootanimation: 6980 6990 (+10)
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zygote64: 10410 10640 (+230)
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zygote: 10410 10640 (+230)
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system_server: 15350 15150 (-200)
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bootanimation ends at: 33790 31230 (-2560)
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Debugging init
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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 -j
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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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