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 91seclabel <securitycontext> 92 Change to securitycontext before exec'ing this service. 93 Primarily for use by services run from the rootfs, e.g. ueventd, adbd. 94 Services on the system partition can instead use policy-defined transitions 95 based on their file security context. 96 If not specified and no transition is defined in policy, defaults to the init context. 97 98oneshot 99 Do not restart the service when it exits. 100 101class <name> 102 Specify a class name for the service. All services in a 103 named class may be started or stopped together. A service 104 is in the class "default" if one is not specified via the 105 class option. 106 107onrestart 108 Execute a Command (see below) when service restarts. 109 110Triggers 111-------- 112 Triggers are strings which can be used to match certain kinds 113 of events and used to cause an action to occur. 114 115boot 116 This is the first trigger that will occur when init starts 117 (after /init.conf is loaded) 118 119<name>=<value> 120 Triggers of this form occur when the property <name> is set 121 to the specific value <value>. 122 123device-added-<path> 124device-removed-<path> 125 Triggers of these forms occur when a device node is added 126 or removed. 127 128service-exited-<name> 129 Triggers of this form occur when the specified service exits. 130 131 132Commands 133-------- 134 135exec <path> [ <argument> ]* 136 Fork and execute a program (<path>). This will block until 137 the program completes execution. It is best to avoid exec 138 as unlike the builtin commands, it runs the risk of getting 139 init "stuck". (??? maybe there should be a timeout?) 140 141export <name> <value> 142 Set the environment variable <name> equal to <value> in the 143 global environment (which will be inherited by all processes 144 started after this command is executed) 145 146ifup <interface> 147 Bring the network interface <interface> online. 148 149import <filename> 150 Parse an init config file, extending the current configuration. 151 152hostname <name> 153 Set the host name. 154 155chdir <directory> 156 Change working directory. 157 158chmod <octal-mode> <path> 159 Change file access permissions. 160 161chown <owner> <group> <path> 162 Change file owner and group. 163 164chroot <directory> 165 Change process root directory. 166 167class_start <serviceclass> 168 Start all services of the specified class if they are 169 not already running. 170 171class_stop <serviceclass> 172 Stop all services of the specified class if they are 173 currently running. 174 175domainname <name> 176 Set the domain name. 177 178insmod <path> 179 Install the module at <path> 180 181mkdir <path> [mode] [owner] [group] 182 Create a directory at <path>, optionally with the given mode, owner, and 183 group. If not provided, the directory is created with permissions 755 and 184 owned by the root user and root group. 185 186mount <type> <device> <dir> [ <mountoption> ]* 187 Attempt to mount the named device at the directory <dir> 188 <device> may be of the form mtd@name to specify a mtd block 189 device by name. 190 <mountoption>s include "ro", "rw", "remount", "noatime", ... 191 192restorecon <path> 193 Restore the file named by <path> to the security context specified 194 in the file_contexts configuration. 195 Not required for directories created by the init.rc as these are 196 automatically labeled correctly by init. 197 198setcon <securitycontext> 199 Set the current process security context to the specified string. 200 This is typically only used from early-init to set the init context 201 before any other process is started. 202 203setenforce 0|1 204 Set the SELinux system-wide enforcing status. 205 0 is permissive (i.e. log but do not deny), 1 is enforcing. 206 207setkey 208 TBD 209 210setprop <name> <value> 211 Set system property <name> to <value>. 212 213setrlimit <resource> <cur> <max> 214 Set the rlimit for a resource. 215 216setsebool <name> <value> 217 Set SELinux boolean <name> to <value>. 218 <value> may be 1|true|on or 0|false|off 219 220start <service> 221 Start a service running if it is not already running. 222 223stop <service> 224 Stop a service from running if it is currently running. 225 226symlink <target> <path> 227 Create a symbolic link at <path> with the value <target> 228 229sysclktz <mins_west_of_gmt> 230 Set the system clock base (0 if system clock ticks in GMT) 231 232trigger <event> 233 Trigger an event. Used to queue an action from another 234 action. 235 236wait <path> [ <timeout> ] 237 Poll for the existence of the given file and return when found, 238 or the timeout has been reached. If timeout is not specified it 239 currently defaults to five seconds. 240 241write <path> <string> [ <string> ]* 242 Open the file at <path> and write one or more strings 243 to it with write(2) 244 245 246Properties 247---------- 248Init updates some system properties to provide some insight into 249what it's doing: 250 251init.action 252 Equal to the name of the action currently being executed or "" if none 253 254init.command 255 Equal to the command being executed or "" if none. 256 257init.svc.<name> 258 State of a named service ("stopped", "running", "restarting") 259 260 261Example init.conf 262----------------- 263 264# not complete -- just providing some examples of usage 265# 266on boot 267 export PATH /sbin:/system/sbin:/system/bin 268 export LD_LIBRARY_PATH /system/lib 269 270 mkdir /dev 271 mkdir /proc 272 mkdir /sys 273 274 mount tmpfs tmpfs /dev 275 mkdir /dev/pts 276 mkdir /dev/socket 277 mount devpts devpts /dev/pts 278 mount proc proc /proc 279 mount sysfs sysfs /sys 280 281 write /proc/cpu/alignment 4 282 283 ifup lo 284 285 hostname localhost 286 domainname localhost 287 288 mount yaffs2 mtd@system /system 289 mount yaffs2 mtd@userdata /data 290 291 import /system/etc/init.conf 292 293 class_start default 294 295service adbd /sbin/adbd 296 user adb 297 group adb 298 299service usbd /system/bin/usbd -r 300 user usbd 301 group usbd 302 socket usbd 666 303 304service zygote /system/bin/app_process -Xzygote /system/bin --zygote 305 socket zygote 666 306 307service runtime /system/bin/runtime 308 user system 309 group system 310 311on device-added-/dev/compass 312 start akmd 313 314on device-removed-/dev/compass 315 stop akmd 316 317service akmd /sbin/akmd 318 disabled 319 user akmd 320 group akmd 321 322Debugging notes 323--------------- 324By default, programs executed by init will drop stdout and stderr into 325/dev/null. To help with debugging, you can execute your program via the 326Andoird program logwrapper. This will redirect stdout/stderr into the 327Android logging system (accessed via logcat). 328 329For example 330service akmd /system/bin/logwrapper /sbin/akmd 331