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> [ <seclabel> ] ] ] 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 'seclabel' is the SELinux security context for the socket. 78 It defaults to the service security context, as specified by seclabel or 79 computed based on the service executable file security context. 80 81 user <username> 82 Change to username before exec'ing this service. 83 Currently defaults to root. (??? probably should default to nobody) 84 Currently, if your process requires linux capabilities then you cannot use 85 this command. You must instead request the capabilities in-process while 86 still root, and then drop to your desired uid. 87 88 group <groupname> [ <groupname> ]* 89 Change to groupname before exec'ing this service. Additional 90 groupnames beyond the (required) first one are used to set the 91 supplemental groups of the process (via setgroups()). 92 Currently defaults to root. (??? probably should default to nobody) 93 94 seclabel <seclabel> 95 Change to 'seclabel' before exec'ing this service. 96 Primarily for use by services run from the rootfs, e.g. ueventd, adbd. 97 Services on the system partition can instead use policy-defined transitions 98 based on their file security context. 99 If not specified and no transition is defined in policy, defaults to the init context. 100 101 oneshot 102 Do not restart the service when it exits. 103 104 class <name> 105 Specify a class name for the service. All services in a 106 named class may be started or stopped together. A service 107 is in the class "default" if one is not specified via the 108 class option. 109 110 onrestart 111 Execute a Command (see below) when service restarts. 112 113 writepid <file...> 114 Write the child's pid to the given files when it forks. Meant for 115 cgroup/cpuset usage. 116 117 118 Triggers 119 -------- 120 Triggers are strings which can be used to match certain kinds 121 of events and used to cause an action to occur. 122 123 boot 124 This is the first trigger that will occur when init starts 125 (after /init.conf is loaded) 126 127 <name>=<value> 128 Triggers of this form occur when the property <name> is set 129 to the specific value <value>. 130 131 One can also test multiple properties to execute a group 132 of commands. For example: 133 134 on property:test.a=1 && property:test.b=1 135 setprop test.c 1 136 137 The above stub sets test.c to 1 only when 138 both test.a=1 and test.b=1 139 140 141 Commands 142 -------- 143 144 bootchart_init 145 Start bootcharting if configured (see below). 146 This is included in the default init.rc. 147 148 chmod <octal-mode> <path> 149 Change file access permissions. 150 151 chown <owner> <group> <path> 152 Change file owner and group. 153 154 class_start <serviceclass> 155 Start all services of the specified class if they are 156 not already running. 157 158 class_stop <serviceclass> 159 Stop and disable all services of the specified class if they are 160 currently running. 161 162 class_reset <serviceclass> 163 Stop all services of the specified class if they are 164 currently running, without disabling them. They can be restarted 165 later using class_start. 166 167 copy <src> <dst> 168 Copies a file. Similar to write, but useful for binary/large 169 amounts of data. 170 171 domainname <name> 172 Set the domain name. 173 174 enable <servicename> 175 Turns a disabled service into an enabled one as if the service did not 176 specify disabled. 177 If the service is supposed to be running, it will be started now. 178 Typically used when the bootloader sets a variable that indicates a specific 179 service should be started when needed. E.g. 180 on property:ro.boot.myfancyhardware=1 181 enable my_fancy_service_for_my_fancy_hardware 182 183 exec [ <seclabel> [ <user> [ <group> ]* ] ] -- <command> [ <argument> ]* 184 Fork and execute command with the given arguments. The command starts 185 after "--" so that an optional security context, user, and supplementary 186 groups can be provided. No other commands will be run until this one 187 finishes. <seclabel> can be a - to denote default. 188 189 export <name> <value> 190 Set the environment variable <name> equal to <value> in the 191 global environment (which will be inherited by all processes 192 started after this command is executed) 193 194 hostname <name> 195 Set the host name. 196 197 ifup <interface> 198 Bring the network interface <interface> online. 199 200 import <filename> 201 Parse an init config file, extending the current configuration. 202 203 insmod <path> 204 Install the module at <path> 205 206 load_all_props 207 Loads properties from /system, /vendor, et cetera. 208 This is included in the default init.rc. 209 210 load_persist_props 211 Loads persistent properties when /data has been decrypted. 212 This is included in the default init.rc. 213 214 loglevel <level> 215 Sets the kernel log level to level. Properties are expanded within <level>. 216 217 mkdir <path> [mode] [owner] [group] 218 Create a directory at <path>, optionally with the given mode, owner, and 219 group. If not provided, the directory is created with permissions 755 and 220 owned by the root user and root group. If provided, the mode, owner and group 221 will be updated if the directory exists already. 222 223 mount_all <fstab> 224 Calls fs_mgr_mount_all on the given fs_mgr-format fstab. 225 226 mount <type> <device> <dir> [ <flag> ]* [<options>] 227 Attempt to mount the named device at the directory <dir> 228 <device> may be of the form mtd@name to specify a mtd block 229 device by name. 230 <flag>s include "ro", "rw", "remount", "noatime", ... 231 <options> include "barrier=1", "noauto_da_alloc", "discard", ... as 232 a comma separated string, eg: barrier=1,noauto_da_alloc 233 234 powerctl 235 Internal implementation detail used to respond to changes to the 236 "sys.powerctl" system property, used to implement rebooting. 237 238 restart <service> 239 Like stop, but doesn't disable the service. 240 241 restorecon <path> [ <path> ]* 242 Restore the file named by <path> to the security context specified 243 in the file_contexts configuration. 244 Not required for directories created by the init.rc as these are 245 automatically labeled correctly by init. 246 247 restorecon_recursive <path> [ <path> ]* 248 Recursively restore the directory tree named by <path> to the 249 security contexts specified in the file_contexts configuration. 250 251 rm <path> 252 Calls unlink(2) on the given path. You might want to 253 use "exec -- rm ..." instead (provided the system partition is 254 already mounted). 255 256 rmdir <path> 257 Calls rmdir(2) on the given path. 258 259 setprop <name> <value> 260 Set system property <name> to <value>. Properties are expanded 261 within <value>. 262 263 setrlimit <resource> <cur> <max> 264 Set the rlimit for a resource. 265 266 start <service> 267 Start a service running if it is not already running. 268 269 stop <service> 270 Stop a service from running if it is currently running. 271 272 swapon_all <fstab> 273 Calls fs_mgr_swapon_all on the given fstab file. 274 275 symlink <target> <path> 276 Create a symbolic link at <path> with the value <target> 277 278 sysclktz <mins_west_of_gmt> 279 Set the system clock base (0 if system clock ticks in GMT) 280 281 trigger <event> 282 Trigger an event. Used to queue an action from another 283 action. 284 285 verity_load_state 286 Internal implementation detail used to load dm-verity state. 287 288 verity_update_state <mount_point> 289 Internal implementation detail used to update dm-verity state and 290 set the partition.<mount_point>.verified properties used by adb remount 291 because fs_mgr can't set them directly itself. 292 293 wait <path> [ <timeout> ] 294 Poll for the existence of the given file and return when found, 295 or the timeout has been reached. If timeout is not specified it 296 currently defaults to five seconds. 297 298 write <path> <content> 299 Open the file at <path> and write a string to it with write(2). 300 If the file does not exist, it will be created. If it does exist, 301 it will be truncated. Properties are expanded within <content>. 302 303 304 Properties 305 ---------- 306 Init updates some system properties to provide some insight into 307 what it's doing: 308 309 init.action 310 Equal to the name of the action currently being executed or "" if none 311 312 init.command 313 Equal to the command being executed or "" if none. 314 315 init.svc.<name> 316 State of a named service ("stopped", "running", "restarting") 317 318 319 Bootcharting 320 ------------ 321 This version of init contains code to perform "bootcharting": generating log 322 files that can be later processed by the tools provided by www.bootchart.org. 323 324 On the emulator, use the -bootchart <timeout> option to boot with bootcharting 325 activated for <timeout> seconds. 326 327 On a device, create /data/bootchart/start with a command like the following: 328 329 adb shell 'echo $TIMEOUT > /data/bootchart/start' 330 331 Where the value of $TIMEOUT corresponds to the desired bootcharted period in 332 seconds. Bootcharting will stop after that many seconds have elapsed. 333 You can also stop the bootcharting at any moment by doing the following: 334 335 adb shell 'echo 1 > /data/bootchart/stop' 336 337 Note that /data/bootchart/stop is deleted automatically by init at the end of 338 the bootcharting. This is not the case with /data/bootchart/start, so don't 339 forget to delete it when you're done collecting data. 340 341 The log files are written to /data/bootchart/. A script is provided to 342 retrieve them and create a bootchart.tgz file that can be used with the 343 bootchart command-line utility: 344 345 sudo apt-get install pybootchartgui 346 # grab-bootchart.sh uses $ANDROID_SERIAL. 347 $ANDROID_BUILD_TOP/system/core/init/grab-bootchart.sh 348 349 One thing to watch for is that the bootchart will show init as if it started 350 running at 0s. You'll have to look at dmesg to work out when the kernel 351 actually started init. 352 353 354 Debugging init 355 -------------- 356 By default, programs executed by init will drop stdout and stderr into 357 /dev/null. To help with debugging, you can execute your program via the 358 Android program logwrapper. This will redirect stdout/stderr into the 359 Android logging system (accessed via logcat). 360 361 For example 362 service akmd /system/bin/logwrapper /sbin/akmd 363 364 For quicker turnaround when working on init itself, use: 365 366 mm -j 367 m ramdisk-nodeps 368 m bootimage-nodeps 369 adb reboot bootloader 370 fastboot boot $ANDROID_PRODUCT_OUT/boot.img 371 372 Alternatively, use the emulator: 373 374 emulator -partition-size 1024 -verbose -show-kernel -no-window 375 376 You might want to call klog_set_level(6) after the klog_init() call 377 so you see the kernel logging in dmesg (or the emulator output). 378
