2 Creating a First Target System
2.1 Introduction
Often it is not desirable to use an Erlang/OTP system as is. A developer may create new Erlang/OTP compliant applications for a particular purpose, and several original Erlang/OTP applications may be irrelevant for the purpose in question. Thus, there is a need to be able to create a new system based on a given Erlang/OTP system, where dispensable applications are removed, and a set of new applications that are included in the new system. Documentation and source code is irrelevant and is therefore not included in the new system.
This chapter is about creating such a system, which we call a target system.
In the following sections we consider creating target systems with different requirements of functionality:
- a basic target system that can be started by calling the ordinary
erl
script,
- a simple target system where also code replacement in run-time can be performed, and
- an embedded target system where there is also support for logging output from the system to file for later inspection, and where the system can be started automatically at boot time.
We only consider the case when Erlang/OTP is running on a UNIX system.
There is an example Erlang module
target_system.erl
that contains functions for creating and installing a target system. That module is used in the examples below. The source code of the module is listed at the end of this chapter.2.2 Creating a Target System
It is assumed that you have a working Erlang/OTP system (which you can start with the command
erl
).Step 1. First create a
.rel
file (see the rel(4) manual page for details) that specifies theerts
version and lists all applications that should be included in the new basic target system. An example is the followingmysystem.rel
file:%% mysystem.rel {release, {"MYSYSTEM", "FIRST"}, {erts, "5.1"}, [{kernel, "2.7"}, {stdlib, "1.10"}, {sasl, "1.9.3"}, {pea, "1.0"}]}.The listed applications are not only original Erlang/OTP applications but possibly also new applications that you have written yourself (here examplified by the application
pea
).Step 2. From the directory where the
mysystem.rel
andplain.rel
files reside, start the Erlang/OTP system:erl -pa /home/user/target_system/myapps/pea-1.0/ebinwhere also the path to the
pea-1.0
ebin directory is provided.Step 2. Now create the target system:
1> target_system:create("mysystem").The
target_system:create/1
function does the following:
- Reads the
mysystem.rel
file, and creates a new fileplain.rel
which is identical to former, except that it only lists thekernel
andstdlib
applications.
- From the
mysystem.rel
andplain.rel
files creates the filesmysystem.script
,mysystem.boot
,plain.script
, andplain.boot
through a call tosystools:make_script/2
.
- Creates the file
mysystem.tar.gz
by a call tosystools:make_tar/2
. That file has the following contents:
erts-5.1/bin/ releases/FIRST/start.boot releases/mysystem.rel lib/kernel-2.7/ lib/stdlib-1.10/ lib/sasl-1.9.3/ lib/pea-1.0/The filereleases/FIRST/start.boot
is a copy of ourmysystem.boot
, and a copy of the originalmysystem.rel
has been put in thereleases
directory.
- Creates the temporary directory
tmp
and extracts the tar filemysystem.tar.gz
into that directory.
- Deletes the
erl
andstart
files fromtmp/erts-5.1/bin
. XXX Why.
- Creates the directory
tmp/bin
.
- Copies the previously creates file
plain.boot
totmp/bin/start.boot
.
- Copies the files
epmd
,run_erl
, andto_erl
from the directorytmp/erts-5.1/bin
to the directorytmp/bin
.
- Creates the file
tmp/releases/start_erl.data
with the contents "5.1 FIRST".
- Recreates the file
mysystem.tar.gz
from the directories in the directorytmp
, and removestmp
.
2.3 Installing a Target System
Step 3. Install the created target system in a suitable directory.
3> target_system:install("mysystem", "/usr/local/erl-target").The function
target_system:install/2
does the following:
- Extracts the tar file
mysystem.tar.gz
into the target directory/usr/local/erl-target
.
- In the target directory reads the file
releases/start_erl.data
in order to find the Erlang runtime system version ("5.1").
- Substitutes
%FINAL_ROOTDIR%
and%EMU%
for/usr/local/erl-target
andbeam
, respectively, in the fileserl.src
,start.src
, andstart_erl.src
of the targeterts-5.1/bin
directory, and puts the resulting fileserl
,start
, andrun_erl
in the targetbin
directory.
- Finally the target
releases/RELEASES
file is created from data in thereleases/mysystem.rel
file.
2.4 Starting a Target System
Now we have a target system that can be started in various ways.
We start it as a basic target system by invoking
/usr/local/erl-target/erlwhere only the
kernel
andstdlib
applications are started, i.e. the system is started as an ordinary development system. There are only two files needed for all this to work:bin/erl
file (obtained fromerts-5.1/bin/erl.src
) and thebin/start.boot
file (a copy ofplain.boot
).We can also start a distributed system (requires
bin/epmd
).To start all applications specified in the original
mysystem.rel
file, use the-boot
flag as follows:/usr/local/erl-target/erl -boot /usr/local/erl-target/releases/FIRST/startWe start a simple target system as above. The only difference is that also the file
releases/RELEASES
is present for code replacement in run-time to work.To start an embedded target system the shell script
bin/start
is used. That shell script callsbin/run_erl
, which in turn callsbin/start_erl
(roughly,start_erl
is an embedded variant oferl
).The shell script
start
is only an example. You should edit it to suite your needs. Typically it is executed when the UNIX system boots.
run_erl
is a wrapper that provides logging of output from the run-time system to file. It also provides a simple mechanism for attaching to the Erlang shell (to_erl
).
start_erl
requires the root directory ("/usr/local/erl-target"
), the releases directory ("/usr/local/erl-target/releases"
), and the location of thestart_erl.data
file. It reads the run-time system version ("5.1"
) and release version ("FIRST"
) from thestart_erl.data
file, starts the run-time system of the version found, and provides-boot
flag specifying the boot file of the release version found ("releases/FIRST/start.boot"
).
start_erl
also assumes that there issys.config
in release version directory ("releases/FIRST/sys.config
). That is the topic of the next section (see below).The
start_erl
shell script should normally not be altered by the user.2.5 System Configuration Parameters
As was pointed out above
start_erl
requires asys.config
in the release version directory ("releases/FIRST/sys.config"
). If there is no such a file, the system start will fail. Hence such a file has to added as well.
If you have system configuration data that are neither file location dependent nor site dependent, it may be convenient to create the
sys.config
early, so that it becomes a part of the target system tar file created bytarget_system:create/1
. In fact, if you create, in the current directory, not only themysystem.rel
file, but also asys.config
file, that latter file will be tacitly put in the apropriate directory.2.6 Differences from the Install Script
The above
install/2
procedure differs somewhat from that of the ordinaryInstall
shell script. In fact,create/1
makes the release package as complete as possible, and leave to theinstall/2
procedure to finish by only considering location dependent files.2.7 Listing of target_system.erl
-module(target_system). -include_lib("kernel/include/file.hrl"). -export([create/1, install/2]). -define(BUFSIZE, 8192). %% Note: RelFileName below is the *stem* without trailing .rel, %% .script etc. %% %% create(RelFileName) %% create(RelFileName) -> RelFile = RelFileName ++ ".rel", io:fwrite("Reading file: \"~s\" ...~n", [RelFile]), {ok, [RelSpec]} = file:consult(RelFile), io:fwrite("Creating file: \"~s\" from \"~s\" ...~n", ["plain.rel", RelFile]), {release, {RelName, RelVsn}, {erts, ErtsVsn}, AppVsns} = RelSpec, PlainRelSpec = {release, {RelName, RelVsn}, {erts, ErtsVsn}, lists:filter(fun({kernel, _}) -> true; ({stdlib, _}) -> true; (_) -> false end, AppVsns) }, {ok, Fd} = file:open("plain.rel", [write]), io:fwrite(Fd, "~p.~n", [PlainRelSpec]), file:close(Fd), io:fwrite("Making \"plain.script\" and \"plain.boot\" files ...~n"), make_script("plain"), io:fwrite("Making \"~s.script\" and \"~s.boot\" files ...~n", [RelFileName, RelFileName]), make_script(RelFileName), TarFileName = io_lib:fwrite("~s.tar.gz", [RelFileName]), io:fwrite("Creating tar file \"~s\" ...~n", [TarFileName]), make_tar(RelFileName), io:fwrite("Creating directory \"tmp\" ...~n"), file:make_dir("tmp"), io:fwrite("Extracting \"~s\" into directory \"tmp\" ...~n", [TarFileName]), extract_tar(TarFileName, "tmp"), TmpBinDir = filename:join(["tmp", "bin"]), ErtsBinDir = filename:join(["tmp", "erts-" ++ ErtsVsn, "bin"]), io:fwrite("Deleting \"erl\" and \"start\" in directory \"~s\" ...~n", [ErtsBinDir]), file:delete(filename:join([ErtsBinDir, "erl"])), file:delete(filename:join([ErtsBinDir, "start"])), io:fwrite("Creating temporary directory \"~s\" ...~n", [TmpBinDir]), file:make_dir(TmpBinDir), io:fwrite("Copying file \"plain.boot\" to \"~s\" ...~n", [filename:join([TmpBinDir, "start.boot"])]), copy_file("plain.boot", filename:join([TmpBinDir, "start.boot"])), io:fwrite("Copying files \"epmd\", \"run_erl\" and \"to_erl\" from \n" "\"~s\" to \"~s\" ...~n", [ErtsBinDir, TmpBinDir]), copy_file(filename:join([ErtsBinDir, "epmd"]), filename:join([TmpBinDir, "epmd"]), [preserve]), copy_file(filename:join([ErtsBinDir, "run_erl"]), filename:join([TmpBinDir, "run_erl"]), [preserve]), copy_file(filename:join([ErtsBinDir, "to_erl"]), filename:join([TmpBinDir, "to_erl"]), [preserve]), StartErlDataFile = filename:join(["tmp", "releases", "start_erl.data"]), io:fwrite("Creating \"~s\" ...~n", [StartErlDataFile]), StartErlData = io_lib:fwrite("~s ~s~n", [ErtsVsn, RelVsn]), write_file(StartErlDataFile, StartErlData), io:fwrite("Recreating tar file \"~s\" from contents in directory " "\"tmp\" ...~n", [TarFileName]), {ok, Tar} = erl_tar:open(TarFileName, [write, compressed]), {ok, Cwd} = file:get_cwd(), file:set_cwd("tmp"), erl_tar:add(Tar, "bin", []), erl_tar:add(Tar, "erts-" ++ ErtsVsn, []), erl_tar:add(Tar, "releases", []), erl_tar:add(Tar, "lib", []), erl_tar:close(Tar), file:set_cwd(Cwd), io:fwrite("Removing directory \"tmp\" ...~n"), remove_dir_tree("tmp"), ok. install(RelFileName, RootDir) -> TarFile = RelFileName ++ ".tar.gz", io:fwrite("Extracting ~s ...~n", [TarFile]), extract_tar(TarFile, RootDir), StartErlDataFile = filename:join([RootDir, "releases", "start_erl.data"]), {ok, StartErlData} = read_txt_file(StartErlDataFile), [ErlVsn, RelVsn| _] = string:tokens(StartErlData, " \n"), ErtsBinDir = filename:join([RootDir, "erts-" ++ ErlVsn, "bin"]), BinDir = filename:join([RootDir, "bin"]), io:fwrite("Substituting in erl.src, start.src and start_erl.src to\n" "form erl, start and start_erl ...\n"), subst_src_scripts(["erl", "start", "start_erl"], ErtsBinDir, BinDir, [{"FINAL_ROOTDIR", RootDir}, {"EMU", "beam"}], [preserve]), io:fwrite("Creating the RELEASES file ...\n"), create_RELEASES(RootDir, filename:join([RootDir, "releases", RelFileName])). %% LOCALS %% make_script(RelFileName) %% make_script(RelFileName) -> Opts = [no_module_tests], systools:make_script(RelFileName, Opts). %% make_tar(RelFileName) %% make_tar(RelFileName) -> RootDir = code:root_dir(), systools:make_tar(RelFileName, [{erts, RootDir}]). %% extract_tar(TarFile, DestDir) %% extract_tar(TarFile, DestDir) -> erl_tar:extract(TarFile, [{cwd, DestDir}, compressed]). create_RELEASES(DestDir, RelFileName) -> release_handler:create_RELEASES(DestDir, RelFileName ++ ".rel"). subst_src_scripts(Scripts, SrcDir, DestDir, Vars, Opts) -> lists:foreach(fun(Script) -> subst_src_script(Script, SrcDir, DestDir, Vars, Opts) end, Scripts). subst_src_script(Script, SrcDir, DestDir, Vars, Opts) -> subst_file(filename:join([SrcDir, Script ++ ".src"]), filename:join([DestDir, Script]), Vars, Opts). subst_file(Src, Dest, Vars, Opts) -> {ok, Conts} = read_txt_file(Src), NConts = subst(Conts, Vars), write_file(Dest, NConts), case lists:member(preserve, Opts) of true -> {ok, FileInfo} = file:read_file_info(Src), file:write_file_info(Dest, FileInfo); false -> ok end. %% subst(Str, Vars) %% Vars = [{Var, Val}] %% Var = Val = string() %% Substitute all occurrences of %Var% for Val in Str, using the list %% of variables in Vars. %% subst(Str, Vars) -> subst(Str, Vars, []). subst([$%, C| Rest], Vars, Result) when $A =< C, C =< $Z -> subst_var([C| Rest], Vars, Result, []); subst([$%, C| Rest], Vars, Result) when $a =< C, C =< $z -> subst_var([C| Rest], Vars, Result, []); subst([$%, C| Rest], Vars, Result) when C == $_ -> subst_var([C| Rest], Vars, Result, []); subst([C| Rest], Vars, Result) -> subst(Rest, Vars, [C| Result]); subst([], _Vars, Result) -> lists:reverse(Result). subst_var([$%| Rest], Vars, Result, VarAcc) -> Key = lists:reverse(VarAcc), case lists:keysearch(Key, 1, Vars) of {value, {Key, Value}} -> subst(Rest, Vars, lists:reverse(Value, Result)); false -> subst(Rest, Vars, [$%| VarAcc ++ [$%| Result]]) end; subst_var([C| Rest], Vars, Result, VarAcc) -> subst_var(Rest, Vars, Result, [C| VarAcc]); subst_var([], Vars, Result, VarAcc) -> subst([], Vars, [VarAcc ++ [$%| Result]]). copy_file(Src, Dest) -> copy_file(Src, Dest, []). copy_file(Src, Dest, Opts) -> {ok, InFd} = file:rawopen(Src, {binary, read}), {ok, OutFd} = file:rawopen(Dest, {binary, write}), do_copy_file(InFd, OutFd), file:close(InFd), file:close(OutFd), case lists:member(preserve, Opts) of true -> {ok, FileInfo} = file:read_file_info(Src), file:write_file_info(Dest, FileInfo); false -> ok end. do_copy_file(InFd, OutFd) -> case file:read(InFd, ?BUFSIZE) of {ok, Bin} -> file:write(OutFd, Bin), do_copy_file(InFd, OutFd); eof -> ok end. write_file(FName, Conts) -> {ok, Fd} = file:open(FName, [write]), file:write(Fd, Conts), file:close(Fd). read_txt_file(File) -> {ok, Bin} = file:read_file(File), {ok, binary_to_list(Bin)}. remove_dir_tree(Dir) -> remove_all_files(".", [Dir]). remove_all_files(Dir, Files) -> lists:foreach(fun(File) -> FilePath = filename:join([Dir, File]), {ok, FileInfo} = file:read_file_info(FilePath), case FileInfo#file_info.type of directory -> {ok, DirFiles} = file:list_dir(FilePath), remove_all_files(FilePath, DirFiles), file:del_dir(FilePath); _ -> file:delete(FilePath) end end, Files).