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Android Init Language
The Android Init Language consists of four broad classes of statements,
which are Actions, Commands, Services, and Options.
whitespace from breaking text into multiple tokens. The backslash,
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 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
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>
Services are programs which init launches and (optionally) restarts
when they exit. Services take the form of:
Options are modifiers to services. They affect how and when init
runs the service.
four minutes, the device will reboot into recovery mode.
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.
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.
'seclabel' is the SELinux security context for the socket.
computed based on the service executable file security context.
user <username>
Change to username before exec'ing this service.
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
supplemental groups of the process (via setgroups()).
seclabel <seclabel>
Change to 'seclabel' before exec'ing this service.
Services on the system partition can instead use policy-defined transitions
based on their file security context.
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.
Execute a Command (see below) when service restarts.
writepid <file...>
cgroup/cpuset usage.
Triggers are strings which can be used to match certain kinds
of events and used to cause an action to occur.
This is the first trigger that will occur when init starts
(after /init.conf is loaded)
Triggers of this form occur when the property <name> is set
to the specific value <value>.
One can also test multiple properties to execute a group
of commands. For example:
on property:test.a=1 && property:test.b=1
setprop test.c 1
The above stub sets test.c to 1 only when
both test.a=1 and test.b=1
Start bootcharting if configured (see below).
This is included in the default init.rc.
chmod <octal-mode> <path>
Change file access permissions.
chown <owner> <group> <path>
Change file owner and group.
class_start <serviceclass>
Start all services of the specified class if they are
not already running.
class_stop <serviceclass>
Stop and disable all services of the specified class if they are
currently running.
class_reset <serviceclass>
Stop all services of the specified class if they are
currently running, without disabling them. They can be restarted
later using class_start.
copy <src> <dst>
amounts of data.
domainname <name>
Set the domain name.
enable <servicename>
specify disabled.
Typically used when the bootloader sets a variable that indicates a specific
service should be started when needed. E.g.
on property:ro.boot.myfancyhardware=1
enable my_fancy_service_for_my_fancy_hardware
exec [ <seclabel> [ <user> [ <group> ]* ] ] -- <command> [ <argument> ]*
Fork and execute command with the given arguments. The command starts
after "--" so that an optional security context, user, and supplementary
finishes. <seclabel> can be a - to denote default.
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)
hostname <name>
Set the host name.
ifup <interface>
Bring the network interface <interface> online.
import <path>
Parse an init config file, extending the current configuration.
If <path> is a directory, each file in the directory is parsed as
a config file. It is not recursive, nested directories will
not be parsed.
insmod <path>
Install the module at <path>
Loads properties from /system, /vendor, et cetera.
This is included in the default init.rc.
Loads persistent properties when /data has been decrypted.
This is included in the default init.rc.
loglevel <level>
Sets the kernel log level to level. Properties are expanded within <level>.
Create a directory at <path>, optionally with the given mode, owner, and
will be updated if the directory exists already.
mount_all <fstab>
Calls fs_mgr_mount_all on the given fs_mgr-format fstab.
mount <type> <device> <dir> [ <flag> ]* [<options>]
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.
<flag>s include "ro", "rw", "remount", "noatime", ...
<options> include "barrier=1", "noauto_da_alloc", "discard", ... as
a comma separated string, eg: barrier=1,noauto_da_alloc
Internal implementation detail used to respond to changes to the
"sys.powerctl" system property, used to implement rebooting.
restart <service>
Like stop, but doesn't disable the service.
restorecon <path> [ <path> ]*
Restore the file named by <path> to the security context specified
in the file_contexts configuration.
Not required for directories created by the init.rc as these are
automatically labeled correctly by init.
restorecon_recursive <path> [ <path> ]*
Recursively restore the directory tree named by <path> to the
security contexts specified in the file_contexts configuration.
rm <path>
use "exec -- rm ..." instead (provided the system partition is
already mounted).
rmdir <path>
Calls rmdir(2) on the given path.
setprop <name> <value>
Set system property <name> to <value>. Properties are expanded
within <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.
swapon_all <fstab>
Calls fs_mgr_swapon_all on the given fstab file.
symlink <target> <path>
Create a symbolic link at <path> with the value <target>
sysclktz <mins_west_of_gmt>
trigger <event>
Trigger an event. Used to queue an action from another
Internal implementation detail used to load dm-verity state.
verity_update_state <mount_point>
Internal implementation detail used to update dm-verity state and
set the partition.<mount_point>.verified properties used by adb remount
because fs_mgr can't set them directly itself.
wait <path> [ <timeout> ]
currently defaults to five seconds.
write <path> <content>
Open the file at <path> and write a string to it with write(2).
it will be truncated. Properties are expanded within <content>.
Init updates some system properties to provide some insight into
what it's doing:
Equal to the name of the action currently being executed or "" if none
Equal to the command being executed or "" if none.
State of a named service ("stopped", "running", "restarting")
This version of init contains code to perform "bootcharting": generating log
files that can be later processed by the tools provided by
On the emulator, use the -bootchart <timeout> option to boot with bootcharting
activated for <timeout> seconds.
On a device, create /data/bootchart/start with a command like the following:
adb shell 'echo $TIMEOUT > /data/bootchart/start'
Where the value of $TIMEOUT corresponds to the desired bootcharted period in
seconds. Bootcharting will stop after that many seconds have elapsed.
You can also stop the bootcharting at any moment by doing the following:
adb shell 'echo 1 > /data/bootchart/stop'
Note that /data/bootchart/stop is deleted automatically by init at the end of
the bootcharting. This is not the case with /data/bootchart/start, so don't
forget to delete it when you're done collecting data.
bootchart command-line utility:
sudo apt-get install pybootchartgui
actually started init.
Comparing two bootcharts
A handy script named can be used to compare the
start/end time of selected processes. The aforementioned
If two such barballs are preserved on the host machine under different
Usage: system/core/init/ base_bootchart_dir
process: baseline experiment (delta)
/init: 50 40 (-10)
zygote64: 10410 10640 (+230)
zygote: 10410 10640 (+230)
system_server: 15350 15150 (-200)
bootanimation ends at: 33790 31230 (-2560)
Debugging init
Android program logwrapper. This will redirect stdout/stderr into the
Android logging system (accessed via logcat).
For example
service akmd /system/bin/logwrapper /sbin/akmd
For quicker turnaround when working on init itself, use:
mm -j
m ramdisk-nodeps
m bootimage-nodeps
adb reboot bootloader
fastboot boot $ANDROID_PRODUCT_OUT/boot.img
Alternatively, use the emulator:
emulator -partition-size 1024 -verbose -show-kernel -no-window
You might want to call klog_set_level(6) after the klog_init() call
so you see the kernel logging in dmesg (or the emulator output).