msantos/prx

an Erlang library for interacting with Unix processes

prx

An Erlang library for Unix process management and system programming tasks.

prx provides:

• a safe, beam-friendly interface to system calls and other POSIX operations

• simple, reliable OS process management by mapping Erlang processes to a hierarchy of system processes

• an interface for privilege separation operations to restrict processes

• operations to isolate processes like containers and jails

Build

$ rebar3 compile

Quick Start

prx has two basic operations: fork and exec.

% Spawn a new system process
{ok, Task} = prx:fork(),

% And a child of the process
{ok, Child} = prx:fork(Task).

After fork()'ing, other calls can be made. For example:

UID = prx:getuid(Task),
PID = prx:getpid(Child).

Calling exec() causes the process I/O to be treated as streams of data:

ok = prx:execvp(Child, ["/bin/cat", "-n"]),
prx:stdin(Child, "test\n"),
receive
    {stdout,Child,Stdout} ->
        Stdout
end.

Usage

• fork and exec /bin/cat

    {ok, Task} = prx:fork(),
    ok = prx:execvp(Task, ["/bin/cat", "-n"],
    prx:stdin(Task, "test\n"),
    receive {stdout, Task, _} = Out -> Out end.
  

• creating a pipeline of child processes

  prx processes can fork child prx processes:

beam
  |-erl_child_setup
  |   `-prx
  |       `-prx

After calling exec, the process tree looks like:

beam
  |-erl_child_setup
  |   `-prx
  |       `-cat

    {ok, Task} = prx:fork(),
    {ok, Child} = prx:fork(Task),
    OSPid = prx:getpid(Child),
    ok = prx:execvp(Child, ["/bin/cat", "-n"],
    prx:stdin(Child, "test\n"),
    receive {stdout, Child, _} = Out -> Out end.

• running cat within a containerized namespace

    application:set_env(prx, options, [{exec, "sudo -n"}]),
    {ok, Task} = prx:fork(),
    {ok, Child} = prx:clone(Task, [clone_newnet, clone_newpid, clone_newipc,
        clone_newuts, clone_newns]),
    OSPid = prx:getpid(Child),
    ok = prx:execvp(Child, ["/bin/cat", "-n"],
    prx:stdin(Child, "test\n"),
    receive {stdout, Child, _} = Out -> Out end.
  

Documentation

https://hexdocs.pm/prx/

See also: alcove

prx's Issues

Can I set beam's own proctitle with this library?

Hello :)

I read the docs but didn't understand if I can set current process title. Sorry, I'm new to Erlang.

We run Erlang 19 and 21 on CentOS 6 and 7 and I would like a simple way to set nice OS process titles. Right now they are just very long beam.smp invokations with a lot of arguments :)

Thanks!

Fail to build

I want to give a try to prx, it seems very interesting. Unfortunately I run into the following error during the build:

[..]/deps/alcove/c_src/sys/clone.c:21:9: note: #pragma message: Support for namespaces using clone(2) enabled
 #pragma message "Support for namespaces using clone(2) enabled"
         ^~~~~~~
[..]/deps/alcove/c_src/sys/setns.c:30:12: error: static declaration of ‘setns’ follows non-static declaration
 static int setns(int fd, int nstype);
            ^~~~~
In file included from /usr/include/sched.h:43,
                 from [..]/deps/alcove/c_src/sys/setns.c:17:
/usr/include/bits/sched.h:94:12: note: previous declaration of ‘setns’ was here
 extern int setns (int __fd, int __nstype) __THROW;
            ^~~~~
make[3]: *** [Makefile:59: [..]/deps/alcove/c_src/../priv/alcove] Error 1
make[3]: Leaving directory '[..]/deps/alcove/c_src'
make[2]: *** [Makefile:37: pre-app] Error 2
make[2]: Leaving directory '[..]/deps/alcove'
make[1]: *** [[..]/erlang.mk:4339: deps] Error 2
make[1]: Leaving directory '[..]/deps/prx'
make: *** [erlang.mk:4339: deps] Error 2

I am running Fedora 28 and OTP-21.0-rc1. I am using erlang.mk to manage my project.
Am i missing any dependency or anything?

Send Stdout after each carriage retrun

I execute a c program with prx which log some useful outputs, I want to receive my outputs line by line (not accumulated in a buffer) after each carriage return .
How can I do it ?