1 2 Android Init Language 3 --------------------- 4 5 The Android Init Language consists of four broad classes of statements, 6 which are Actions, Commands, Services, and Options. 7 8 All of these are line-oriented, consisting of tokens separated by 9 whitespace. The c-style backslash escapes may be used to insert 10 whitespace into a token. Double quotes may also be used to prevent 11 whitespace from breaking text into multiple tokens. The backslash, 12 when it is the last character on a line, may be used for line-folding. 13 14 Lines which start with a # (leading whitespace allowed) are comments. 15 16 Actions and Services implicitly declare a new section. All commands 17 or options belong to the section most recently declared. Commands 18 or options before the first section are ignored. 19 20 Actions and Services have unique names. If a second Action or Service 21 is declared with the same name as an existing one, it is ignored as 22 an error. (??? should we override instead) 23 24 25 Actions 26 ------- 27 Actions are named sequences of commands. Actions have a trigger which 28 is used to determine when the action should occur. When an event 29 occurs which matches an action's trigger, that action is added to 30 the tail of a to-be-executed queue (unless it is already on the 31 queue). 32 33 Each action in the queue is dequeued in sequence and each command in 34 that 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 38 Actions take the form of: 39 40 on <trigger> 41 <command> 42 <command> 43 <command> 44 45 46 Services 47 -------- 48 Services are programs which init launches and (optionally) restarts 49 when they exit. Services take the form of: 50 51 service <name> <pathname> [ <argument> ]* 52 <option> 53 <option> 54 ... 55 56 57 Options 58 ------- 59 Options are modifiers to services. They affect how and when init 60 runs the service. 61 62 critical 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 66 disabled 67 This service will not automatically start with its class. 68 It must be explicitly started by name. 69 70 setenv <name> <value> 71 Set the environment variable <name> to <value> in the launched process. 72 73 socket <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 78 user <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 85 group <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 91 seclabel <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 98 oneshot 99 Do not restart the service when it exits. 100 101 class <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. 106 107 onrestart 108 Execute a Command (see below) when service restarts. 109 110 Triggers 111 -------- 112 Triggers are strings which can be used to match certain kinds 113 of events and used to cause an action to occur. 114 115 boot 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>. 122 123 device-added-<path> 124 device-removed-<path> 125 Triggers of these forms occur when a device node is added 126 or removed. 127 128 service-exited-<name> 129 Triggers of this form occur when the specified service exits. 130 131 132 Commands 133 -------- 134 135 exec <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?) 140 141 export <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) 145 146 ifup <interface> 147 Bring the network interface <interface> online. 148 149 import <filename> 150 Parse an init config file, extending the current configuration. 151 152 hostname <name> 153 Set the host name. 154 155 chdir <directory> 156 Change working directory. 157 158 chmod <octal-mode> <path> 159 Change file access permissions. 160 161 chown <owner> <group> <path> 162 Change file owner and group. 163 164 chroot <directory> 165 Change process root directory. 166 167 class_start <serviceclass> 168 Start all services of the specified class if they are 169 not already running. 170 171 class_stop <serviceclass> 172 Stop all services of the specified class if they are 173 currently running. 174 175 domainname <name> 176 Set the domain name. 177 178 insmod <path> 179 Install the module at <path> 180 181 mkdir <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. 185 186 mount <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", ... 191 192 restorecon <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. 197 198 setcon <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. 202 203 setenforce 0|1 204 Set the SELinux system-wide enforcing status. 205 0 is permissive (i.e. log but do not deny), 1 is enforcing. 206 207 setkey 208 TBD 209 210 setprop <name> <value> 211 Set system property <name> to <value>. 212 213 setrlimit <resource> <cur> <max> 214 Set the rlimit for a resource. 215 216 setsebool <name> <value> 217 Set SELinux boolean <name> to <value>. 218 <value> may be 1|true|on or 0|false|off 219 220 start <service> 221 Start a service running if it is not already running. 222 223 stop <service> 224 Stop a service from running if it is currently running. 225 226 symlink <target> <path> 227 Create a symbolic link at <path> with the value <target> 228 229 sysclktz <mins_west_of_gmt> 230 Set the system clock base (0 if system clock ticks in GMT) 231 232 trigger <event> 233 Trigger an event. Used to queue an action from another 234 action. 235 236 wait <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. 240 241 write <path> <string> [ <string> ]* 242 Open the file at <path> and write one or more strings 243 to it with write(2) 244 245 246 Properties 247 ---------- 248 Init updates some system properties to provide some insight into 249 what it's doing: 250 251 init.action 252 Equal to the name of the action currently being executed or "" if none 253 254 init.command 255 Equal to the command being executed or "" if none. 256 257 init.svc.<name> 258 State of a named service ("stopped", "running", "restarting") 259 260 261 Example init.conf 262 ----------------- 263 264 # not complete -- just providing some examples of usage 265 # 266 on 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 294 295 service adbd /sbin/adbd 296 user adb 297 group adb 298 299 service usbd /system/bin/usbd -r 300 user usbd 301 group usbd 302 socket usbd 666 303 304 service zygote /system/bin/app_process -Xzygote /system/bin --zygote 305 socket zygote 666 306 307 service runtime /system/bin/runtime 308 user system 309 group system 310 311 on device-added-/dev/compass 312 start akmd 313 314 on device-removed-/dev/compass 315 stop akmd 316 317 service akmd /sbin/akmd 318 disabled 319 user akmd 320 group akmd 321 322 Debugging notes 323 --------------- 324 By 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 326 Andoird program logwrapper. This will redirect stdout/stderr into the 327 Android logging system (accessed via logcat). 328 329 For example 330 service akmd /system/bin/logwrapper /sbin/akmd 331