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 oneshot 92 Do not restart the service when it exits. 93 94 class <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. 99 100 onrestart 101 Execute a Command (see below) when service restarts. 102 103 Triggers 104 -------- 105 Triggers are strings which can be used to match certain kinds 106 of events and used to cause an action to occur. 107 108 boot 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>. 115 116 device-added-<path> 117 device-removed-<path> 118 Triggers of these forms occur when a device node is added 119 or removed. 120 121 service-exited-<name> 122 Triggers of this form occur when the specified service exits. 123 124 125 Commands 126 -------- 127 128 exec <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?) 133 134 export <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) 138 139 ifup <interface> 140 Bring the network interface <interface> online. 141 142 import <filename> 143 Parse an init config file, extending the current configuration. 144 145 hostname <name> 146 Set the host name. 147 148 chdir <directory> 149 Change working directory. 150 151 chmod <octal-mode> <path> 152 Change file access permissions. 153 154 chown <owner> <group> <path> 155 Change file owner and group. 156 157 chroot <directory> 158 Change process root directory. 159 160 class_start <serviceclass> 161 Start all services of the specified class if they are 162 not already running. 163 164 class_stop <serviceclass> 165 Stop all services of the specified class if they are 166 currently running. 167 168 domainname <name> 169 Set the domain name. 170 171 insmod <path> 172 Install the module at <path> 173 174 mkdir <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. 178 179 mount <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", ... 184 185 setkey 186 TBD 187 188 setprop <name> <value> 189 Set system property <name> to <value>. 190 191 setrlimit <resource> <cur> <max> 192 Set the rlimit for a resource. 193 194 start <service> 195 Start a service running if it is not already running. 196 197 stop <service> 198 Stop a service from running if it is currently running. 199 200 symlink <target> <path> 201 Create a symbolic link at <path> with the value <target> 202 203 sysclktz <mins_west_of_gmt> 204 Set the system clock base (0 if system clock ticks in GMT) 205 206 trigger <event> 207 Trigger an event. Used to queue an action from another 208 action. 209 210 write <path> <string> [ <string> ]* 211 Open the file at <path> and write one or more strings 212 to it with write(2) 213 214 215 Properties 216 ---------- 217 Init updates some system properties to provide some insight into 218 what it's doing: 219 220 init.action 221 Equal to the name of the action currently being executed or "" if none 222 223 init.command 224 Equal to the command being executed or "" if none. 225 226 init.svc.<name> 227 State of a named service ("stopped", "running", "restarting") 228 229 230 Example init.conf 231 ----------------- 232 233 # not complete -- just providing some examples of usage 234 # 235 on 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 263 264 service adbd /sbin/adbd 265 user adb 266 group adb 267 268 service usbd /system/bin/usbd -r 269 user usbd 270 group usbd 271 socket usbd 666 272 273 service zygote /system/bin/app_process -Xzygote /system/bin --zygote 274 socket zygote 666 275 276 service runtime /system/bin/runtime 277 user system 278 group system 279 280 on device-added-/dev/compass 281 start akmd 282 283 on device-removed-/dev/compass 284 stop akmd 285 286 service akmd /sbin/akmd 287 disabled 288 user akmd 289 group akmd 290 291 Debugging notes 292 --------------- 293 By 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 295 Andoird program logwrapper. This will redirect stdout/stderr into the 296 Android logging system (accessed via logcat). 297 298 For example 299 service akmd /system/bin/logwrapper /sbin/akmd 300
