1init(3) Erlang Module Definition init(3)
2
6 init - Coordination of system startup.
7
9 This module is preloaded and contains the code for the init system
10 process that coordinates the startup of the system. The first function
11 evaluated at startup is boot(BootArgs), where BootArgs is a list of
12 command-line arguments supplied to the Erlang runtime system from the
13 local operating system; see erl(1).
14 init reads the boot script, which contains instructions on how to ini‐
16 tiate the system. For more information about boot scripts, see
17 script(4).
18 init also contains functions to restart, reboot, and stop the system.
20
22 boot(BootArgs) -> no_return()
23 Types:
25 BootArgs = [binary()]
27 Starts the Erlang runtime system. This function is called when
29 the emulator is started and coordinates system startup.
30 BootArgs are all command-line arguments except the emulator
32 flags, that is, flags and plain arguments; see erl(1).
33 init interprets some of the flags, see section Command-Line
35 Flags below. The remaining flags ("user flags") and plain argu‐
36 ments are passed to the init loop and can be retrieved by call‐
37 ing get_arguments/0 and get_plain_arguments/0, respectively.
38 get_argument(Flag) -> {ok, Arg} | error
40 Types:
42 Flag = atom()
44 Arg = [Values :: [string()]]
45 Returns all values associated with the command-line user flag
47 Flag. If Flag is provided several times, each Values is returned
48 in preserved order. Example:
49 % erl -a b c -a d
51 1> init:get_argument(a).
52 {ok,[["b","c"],["d"]]}
53 The following flags are defined automatically and can be
55 retrieved using this function:
56 root:
58 The installation directory of Erlang/OTP, $ROOT:
59 2> init:get_argument(root).
61 {ok,[["/usr/local/otp/releases/otp_beam_solaris8_r10b_patched"]]}
62 progname:
64 The name of the program which started Erlang:
65 3> init:get_argument(progname).
67 {ok,[["erl"]]}
68 home:
70 The home directory (on Unix, the value of $HOME):
71 4> init:get_argument(home).
73 {ok,[["/home/harry"]]}
74 Returns error if no value is associated with Flag.
76 get_arguments() -> Flags
78 Types:
80 Flags = [{Flag :: atom(), Values :: [string()]}]
82 Returns all command-line flags and the system-defined flags, see
84 get_argument/1.
85 get_plain_arguments() -> [Arg]
87 Types:
89 Arg = string()
91 Returns any plain command-line arguments as a list of strings
93 (possibly empty).
94 get_status() -> {InternalStatus, ProvidedStatus}
96 Types:
98 InternalStatus = internal_status()
100 ProvidedStatus = term()
101 internal_status() = starting | started | stopping
102 The current status of the init process can be inspected. During
104 system startup (initialization), InternalStatus is starting, and
105 ProvidedStatus indicates how far the boot script has been inter‐
106 preted. Each {progress, Info} term interpreted in the boot
107 script affects ProvidedStatus, that is, ProvidedStatus gets the
108 value of Info.
109 reboot() -> ok
111 All applications are taken down smoothly, all code is unloaded,
113 and all ports are closed before the system terminates. If com‐
114 mand-line flag -heart was specified, the heart program tries to
115 reboot the system. For more information, see heart(3).
116 To limit the shutdown time, the time init is allowed to spend
118 taking down applications, command-line flag -shutdown_time is to
119 be used.
120 restart() -> ok
122 The system is restarted inside the running Erlang node, which
124 means that the emulator is not restarted. All applications are
125 taken down smoothly, all code is unloaded, and all ports are
126 closed before the system is booted again in the same way as ini‐
127 tially started. The same BootArgs are used again.
128 To limit the shutdown time, the time init is allowed to spend
130 taking down applications, command-line flag -shutdown_time is to
131 be used.
132 script_id() -> Id
134 Types:
136 Id = term()
138 Gets the identity of the boot script used to boot the system. Id
140 can be any Erlang term. In the delivered boot scripts, Id is
141 {Name, Vsn}. Name and Vsn are strings.
142 stop() -> ok
144 The same as stop(0).
146 stop(Status) -> ok
148 Types:
150 Status = integer() >= 0 | string()
152 All applications are taken down smoothly, all code is unloaded,
154 and all ports are closed before the system terminates by calling
155 halt(Status). If command-line flag -heart was specified, the
156 heart program is terminated before the Erlang node terminates.
157 For more information, see heart(3).
158 To limit the shutdown time, the time init is allowed to spend
160 taking down applications, command-line flag -shutdown_time is to
161 be used.
162
164 Warning:
165 The support for loading of code from archive files is experimental. The
166 only purpose of releasing it before it is ready is to obtain early
167 feedback. The file format, semantics, interfaces, and so on, can be
168 changed in a future release. The -code_path_choice flag is also experi‐
169 mental.
170 The init module interprets the following command-line flags:
173 --:
175 Everything following -- up to the next flag is considered plain
176 arguments and can be retrieved using get_plain_arguments/0.
177 -code_path_choice Choice:
179 Can be set to strict or relaxed. It controls how each directory in
180 the code path is to be interpreted:
181 * Strictly as it appears in the boot script, or
183 * init is to be more relaxed and try to find a suitable directory
185 if it can choose from a regular ebin directory and an ebin direc‐
186 tory in an archive file.
187 This flag is particular useful when you want to elaborate with code
189 loading from archives without editing the boot script. For more
190 information about interpretation of boot scripts, see script(4).
191 The flag has also a similar effect on how the code server works;
192 see code(3).
193 -epmd_module Module:
195 Specifies the module to use for registration and lookup of node
196 names. Defaults to erl_epmd.
197 -eval Expr:
199 Scans, parses, and evaluates an arbitrary expression Expr during
200 system initialization. If any of these steps fail (syntax error,
201 parse error, or exception during evaluation), Erlang stops with an
202 error message. In the following example Erlang is used as a hexa‐
203 decimal calculator:
204 % erl -noshell -eval 'R = 16#1F+16#A0, io:format("~.16B~n", [R])' \\
206 -s erlang halt
207 BF
208 If multiple -eval expressions are specified, they are evaluated
210 sequentially in the order specified. -eval expressions are evalu‐
211 ated sequentially with -s and -run function calls (this also in the
212 order specified). As with -s and -run, an evaluation that does not
213 terminate blocks the system initialization process.
214 -extra:
216 Everything following -extra is considered plain arguments and can
217 be retrieved using get_plain_arguments/0.
218 -run Mod [Func [Arg1, Arg2, ...]]:
220 Evaluates the specified function call during system initialization.
221 Func defaults to start. If no arguments are provided, the function
222 is assumed to be of arity 0. Otherwise it is assumed to be of arity
223 1, taking the list [Arg1,Arg2,...] as argument. All arguments are
224 passed as strings. If an exception is raised, Erlang stops with an
225 error message.
226 Example:
228 % erl -run foo -run foo bar -run foo bar baz 1 2
230 This starts the Erlang runtime system and evaluates the following
232 functions:
233 foo:start()
235 foo:bar()
236 foo:bar(["baz", "1", "2"]).
237 The functions are executed sequentially in an initialization
239 process, which then terminates normally and passes control to the
240 user. This means that a -run call that does not return blocks fur‐
241 ther processing; to avoid this, use some variant of spawn in such
242 cases.
243 -s Mod [Func [Arg1, Arg2, ...]]:
245 Evaluates the specified function call during system initialization.
246 Func defaults to start. If no arguments are provided, the function
247 is assumed to be of arity 0. Otherwise it is assumed to be of arity
248 1, taking the list [Arg1,Arg2,...] as argument. All arguments are
249 passed as atoms. If an exception is raised, Erlang stops with an
250 error message.
251 Example:
253 % erl -s foo -s foo bar -s foo bar baz 1 2
255 This starts the Erlang runtime system and evaluates the following
257 functions:
258 foo:start()
260 foo:bar()
261 foo:bar([baz, '1', '2']).
262 The functions are executed sequentially in an initialization
264 process, which then terminates normally and passes control to the
265 user. This means that a -s call that does not return blocks further
266 processing; to avoid this, use some variant of spawn in such cases.
267 Because of the limited length of atoms, it is recommended to use
269 -run instead.
270
272 % erl -- a b -children thomas claire -ages 7 3 -- x y
273 1> init:get_plain_arguments().
275 ["a","b","x","y"]
276 2> init:get_argument(children).
277 {ok,[["thomas","claire"]]}
278 3> init:get_argument(ages).
279 {ok, [["7","3"]]}
280 4> init:get_argument(silly).
281 error
282
284 erl_prim_loader(3), heart(3)
285Ericsson AB erts 10.7.1 init(3)