1 2Android Init Language 3--------------------- 4 5The Android Init Language consists of four broad classes of statements, 6which are Actions, Commands, Services, and Options. 7 8All of these are line-oriented, consisting of tokens separated by 9whitespace. The c-style backslash escapes may be used to insert 10whitespace into a token. Double quotes may also be used to prevent 11whitespace from breaking text into multiple tokens. The backslash, 12when it is the last character on a line, may be used for line-folding. 13 14Lines which start with a # (leading whitespace allowed) are comments. 15 16Actions and Services implicitly declare a new section. All commands 17or options belong to the section most recently declared. Commands 18or options before the first section are ignored. 19 20Actions and Services have unique names. If a second Action or Service 21is declared with the same name as an existing one, it is ignored as 22an error. (??? should we override instead) 23 24 25Actions 26------- 27Actions are named sequences of commands. Actions have a trigger which 28is used to determine when the action should occur. When an event 29occurs which matches an action's trigger, that action is added to 30the tail of a to-be-executed queue (unless it is already on the 31queue). 32 33Each action in the queue is dequeued in sequence and each command in 34that action is executed in sequence. Init handles other activities 35(device creation/destruction, property setting, process restarting) 36"between" the execution of the commands in activities. 37 38Actions take the form of: 39 40on <trigger> 41 <command> 42 <command> 43 <command> 44 45 46Services 47-------- 48Services are programs which init launches and (optionally) restarts 49when they exit. Services take the form of: 50 51service <name> <pathname> [ <argument> ]* 52 <option> 53 <option> 54 ... 55 56 57Options 58------- 59Options are modifiers to services. They affect how and when init 60runs the service. 61 62critical 63 This is a device-critical service. If it exits more than four times in 64 four minutes, the device will reboot into recovery mode. 65 66disabled 67 This service will not automatically start with its class. 68 It must be explicitly started by name. 69 70setenv <name> <value> 71 Set the environment variable <name> to <value> in the launched process. 72 73socket <name> <type> <perm> [ <user> [ <group> ] ] 74 Create a unix domain socket named /dev/socket/<name> and pass 75 its fd to the launched process. <type> must be "dgram", "stream" or "seqpacket". 76 User and group default to 0. 77 78user <username> 79 Change to username before exec'ing this service. 80 Currently defaults to root. (??? probably should default to nobody) 81 Currently, if your process requires linux capabilities then you cannot use 82 this command. You must instead request the capabilities in-process while 83 still root, and then drop to your desired uid. 84 85group <groupname> [ <groupname> ]* 86 Change to groupname before exec'ing this service. Additional 87 groupnames beyond the (required) first one are used to set the 88 supplemental groups of the process (via setgroups()). 89 Currently defaults to root. (??? probably should default to nobody) 90 91oneshot 92 Do not restart the service when it exits. 93 94class <name> 95 Specify a class name for the service. All services in a 96 named class may be started or stopped together. A service 97 is in the class "default" if one is not specified via the 98 class option. 99 100onrestart 101 Execute a Command (see below) when service restarts. 102 103Triggers 104-------- 105 Triggers are strings which can be used to match certain kinds 106 of events and used to cause an action to occur. 107 108boot 109 This is the first trigger that will occur when init starts 110 (after /init.conf is loaded) 111 112<name>=<value> 113 Triggers of this form occur when the property <name> is set 114 to the specific value <value>. 115 116device-added-<path> 117device-removed-<path> 118 Triggers of these forms occur when a device node is added 119 or removed. 120 121service-exited-<name> 122 Triggers of this form occur when the specified service exits. 123 124 125Commands 126-------- 127 128exec <path> [ <argument> ]* 129 Fork and execute a program (<path>). This will block until 130 the program completes execution. It is best to avoid exec 131 as unlike the builtin commands, it runs the risk of getting 132 init "stuck". (??? maybe there should be a timeout?) 133 134export <name> <value> 135 Set the environment variable <name> equal to <value> in the 136 global environment (which will be inherited by all processes 137 started after this command is executed) 138 139ifup <interface> 140 Bring the network interface <interface> online. 141 142import <filename> 143 Parse an init config file, extending the current configuration. 144 145hostname <name> 146 Set the host name. 147 148chdir <directory> 149 Change working directory. 150 151chmod <octal-mode> <path> 152 Change file access permissions. 153 154chown <owner> <group> <path> 155 Change file owner and group. 156 157chroot <directory> 158 Change process root directory. 159 160class_start <serviceclass> 161 Start all services of the specified class if they are 162 not already running. 163 164class_stop <serviceclass> 165 Stop all services of the specified class if they are 166 currently running. 167 168domainname <name> 169 Set the domain name. 170 171insmod <path> 172 Install the module at <path> 173 174mkdir <path> [mode] [owner] [group] 175 Create a directory at <path>, optionally with the given mode, owner, and 176 group. If not provided, the directory is created with permissions 755 and 177 owned by the root user and root group. 178 179mount <type> <device> <dir> [ <mountoption> ]* 180 Attempt to mount the named device at the directory <dir> 181 <device> may be of the form mtd@name to specify a mtd block 182 device by name. 183 <mountoption>s include "ro", "rw", "remount", "noatime", ... 184 185setkey 186 TBD 187 188setprop <name> <value> 189 Set system property <name> to <value>. 190 191setrlimit <resource> <cur> <max> 192 Set the rlimit for a resource. 193 194start <service> 195 Start a service running if it is not already running. 196 197stop <service> 198 Stop a service from running if it is currently running. 199 200symlink <target> <path> 201 Create a symbolic link at <path> with the value <target> 202 203sysclktz <mins_west_of_gmt> 204 Set the system clock base (0 if system clock ticks in GMT) 205 206trigger <event> 207 Trigger an event. Used to queue an action from another 208 action. 209 210write <path> <string> [ <string> ]* 211 Open the file at <path> and write one or more strings 212 to it with write(2) 213 214 215Properties 216---------- 217Init updates some system properties to provide some insight into 218what it's doing: 219 220init.action 221 Equal to the name of the action currently being executed or "" if none 222 223init.command 224 Equal to the command being executed or "" if none. 225 226init.svc.<name> 227 State of a named service ("stopped", "running", "restarting") 228 229 230Example init.conf 231----------------- 232 233# not complete -- just providing some examples of usage 234# 235on boot 236 export PATH /sbin:/system/sbin:/system/bin 237 export LD_LIBRARY_PATH /system/lib 238 239 mkdir /dev 240 mkdir /proc 241 mkdir /sys 242 243 mount tmpfs tmpfs /dev 244 mkdir /dev/pts 245 mkdir /dev/socket 246 mount devpts devpts /dev/pts 247 mount proc proc /proc 248 mount sysfs sysfs /sys 249 250 write /proc/cpu/alignment 4 251 252 ifup lo 253 254 hostname localhost 255 domainname localhost 256 257 mount yaffs2 mtd@system /system 258 mount yaffs2 mtd@userdata /data 259 260 import /system/etc/init.conf 261 262 class_start default 263 264service adbd /sbin/adbd 265 user adb 266 group adb 267 268service usbd /system/bin/usbd -r 269 user usbd 270 group usbd 271 socket usbd 666 272 273service zygote /system/bin/app_process -Xzygote /system/bin --zygote 274 socket zygote 666 275 276service runtime /system/bin/runtime 277 user system 278 group system 279 280on device-added-/dev/compass 281 start akmd 282 283on device-removed-/dev/compass 284 stop akmd 285 286service akmd /sbin/akmd 287 disabled 288 user akmd 289 group akmd 290 291Debugging notes 292--------------- 293By default, programs executed by init will drop stdout and stderr into 294/dev/null. To help with debugging, you can execute your program via the 295Andoird program logwrapper. This will redirect stdout/stderr into the 296Android logging system (accessed via logcat). 297 298For example 299service akmd /system/bin/logwrapper /sbin/akmd 300