module Process

Terminate execution immediately, effectively by calling Kernel.exit(false). If msg is given, it is written to STDERR prior to terminating.

VALUE
rb_f_abort(int argc, VALUE *argv)
{
    rb_secure(4);
    if (argc == 0) {
        if (!NIL_P(GET_THREAD()->errinfo)) {
            ruby_error_print();
        }
        rb_exit(EXIT_FAILURE);
    }
    else {
        VALUE args[2];

        rb_scan_args(argc, argv, "1", &args[1]);
        StringValue(argv[0]);
        rb_io_puts(argc, argv, rb_stderr);
        args[0] = INT2NUM(EXIT_FAILURE);
        rb_exc_raise(rb_class_new_instance(2, args, rb_eSystemExit));
    }

    UNREACHABLE;
}

Detach the process from controlling terminal and run in the background as system daemon. Unless the argument nochdir is true (i.e. non false), it changes the current working directory to the root (“/”). Unless the argument noclose is true, daemon() will redirect standard input, standard output and standard error to /dev/null. Return zero on success, or raise one of Errno::*.

static VALUE
proc_daemon(int argc, VALUE *argv)
{
    VALUE nochdir, noclose;
    int n;

    rb_secure(2);
    rb_scan_args(argc, argv, "02", &nochdir, &noclose);

    prefork();
    n = rb_daemon(RTEST(nochdir), RTEST(noclose));
    if (n < 0) rb_sys_fail("daemon");
    return INT2FIX(n);
}

Some operating systems retain the status of terminated child processes until the parent collects that status (normally using some variant of wait(). If the parent never collects this status, the child stays around as a zombie process. Process::detach prevents this by setting up a separate Ruby thread whose sole job is to reap the status of the process pid when it terminates. Use detach only when you do not intent to explicitly wait for the child to terminate.

The waiting thread returns the exit status of the detached process when it terminates, so you can use Thread#join to know the result. If specified pid is not a valid child process ID, the thread returns nil immediately.

The waiting thread has pid method which returns the pid.

In this first example, we don't reap the first child process, so it appears as a zombie in the process status display.

p1 = fork { sleep 0.1 }
p2 = fork { sleep 0.2 }
Process.waitpid(p2)
sleep 2
system("ps -ho pid,state -p #{p1}")

produces:

27389 Z

In the next example, Process::detach is used to reap the child automatically.

p1 = fork { sleep 0.1 }
p2 = fork { sleep 0.2 }
Process.detach(p1)
Process.waitpid(p2)
sleep 2
system("ps -ho pid,state -p #{p1}")

(produces no output)

static VALUE
proc_detach(VALUE obj, VALUE pid)
{
    rb_secure(2);
    return rb_detach_process(NUM2PIDT(pid));
}

Returns the effective group ID for this process. Not available on all platforms.

Process.egid   #=> 500

static VALUE
proc_getegid(VALUE obj)
{
    rb_gid_t egid = getegid();

    return GIDT2NUM(egid);
}

Sets the effective group ID for this process. Not available on all platforms.

static VALUE
proc_setegid(VALUE obj, VALUE egid)
{
#if defined(HAVE_SETRESGID) || defined(HAVE_SETREGID) || defined(HAVE_SETEGID) || defined(HAVE_SETGID)
    rb_gid_t gid;
#endif

    check_gid_switch();

#if defined(HAVE_SETRESGID) || defined(HAVE_SETREGID) || defined(HAVE_SETEGID) || defined(HAVE_SETGID)
    gid = OBJ2GID(egid);
#endif

#if defined(HAVE_SETRESGID)
    if (setresgid(-1, gid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREGID
    if (setregid(-1, gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETEGID
    if (setegid(gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETGID
    if (gid == getgid()) {
        if (setgid(gid) < 0) rb_sys_fail(0);
    }
    else {
        rb_notimplement();
    }
#else
    rb_notimplement();
#endif
    return egid;
}

Returns the effective user ID for this process.

Process.euid   #=> 501

static VALUE
proc_geteuid(VALUE obj)
{
    rb_uid_t euid = geteuid();
    return UIDT2NUM(euid);
}

Sets the effective user ID for this process. Not available on all platforms.

static VALUE
proc_seteuid_m(VALUE mod, VALUE euid)
{
    check_uid_switch();
    proc_seteuid(OBJ2UID(euid));
    return euid;
}

Replaces the current process by running the given external command. command… is one of following forms.

commandline                 : command line string which is passed to the standard shell
cmdname, arg1, ...          : command name and one or more arguments (no shell)
[cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)

If single string is given as the command, it is taken as a command line that is subject to shell expansion before being executed.

The standard shell means always "/bin/sh" on Unix-like systems, ENV["RUBYSHELL"] or ENV["COMSPEC"] on Windows NT series, and similar.

If two or more string given, the first is taken as a command name and the rest are passed as parameters to command with no shell expansion.

If a two-element array at the beginning of the command, the first element is the command to be executed, and the second argument is used as the argv[0] value, which may show up in process listings.

In order to execute the command, one of the exec(2) system calls is used, so the running command may inherit some of the environment of the original program (including open file descriptors). This behavior is modified by env and options. See spawn for details.

Raises SystemCallError if the command couldn't execute (typically Errno::ENOENT when it was not found).

This method modifies process attributes according to options (details described in spawn) before exec(2) system call. The modified attributes may be retained when exec(2) system call fails. For example, hard resource limits is not restorable. If it is not acceptable, consider to create a child process using spawn or system.

exec "echo *"       # echoes list of files in current directory
# never get here

exec "echo", "*"    # echoes an asterisk
# never get here

VALUE
rb_f_exec(int argc, VALUE *argv)
{
    VALUE execarg_obj, fail_str;
    struct rb_execarg *eargp;
#define CHILD_ERRMSG_BUFLEN 80
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };

    execarg_obj = rb_execarg_new(argc, argv, TRUE);
    eargp = rb_execarg_get(execarg_obj);
    rb_execarg_fixup(execarg_obj);
    fail_str = eargp->use_shell ? eargp->invoke.sh.shell_script : eargp->invoke.cmd.command_name;

#if defined(__APPLE__) || defined(__HAIKU__)
    rb_exec_without_timer_thread(eargp, errmsg, sizeof(errmsg));
#else
    rb_exec_async_signal_safe(eargp, errmsg, sizeof(errmsg));
#endif
    RB_GC_GUARD(execarg_obj);
    if (errmsg[0])
        rb_sys_fail(errmsg);
    rb_sys_fail_str(fail_str);
    return Qnil;                /* dummy */
}

Initiates the termination of the Ruby script by raising the SystemExit exception. This exception may be caught. The optional parameter is used to return a status code to the invoking environment. true and FALSE of status means success and failure respectively. The interpretation of other integer values are system dependent.

begin
  exit
  puts "never get here"
rescue SystemExit
  puts "rescued a SystemExit exception"
end
puts "after begin block"

produces:

rescued a SystemExit exception
after begin block

Just prior to termination, Ruby executes any at_exit functions (see Kernel::at_exit) and runs any object finalizers (see ObjectSpace.define_finalizer).

at_exit { puts "at_exit function" }
ObjectSpace.define_finalizer("string",  proc { puts "in finalizer" })
exit

produces:

at_exit function
in finalizer

VALUE
rb_f_exit(int argc, VALUE *argv)
{
    VALUE status;
    int istatus;

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
        istatus = exit_status_code(status);
    }
    else {
        istatus = EXIT_SUCCESS;
    }
    rb_exit(istatus);

    UNREACHABLE;
}

Exits the process immediately. No exit handlers are run. status is returned to the underlying system as the exit status.

Process.exit!(true)

static VALUE
rb_f_exit_bang(int argc, VALUE *argv, VALUE obj)
{
    VALUE status;
    int istatus;

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
        istatus = exit_status_code(status);
    }
    else {
        istatus = EXIT_FAILURE;
    }
    _exit(istatus);

    UNREACHABLE;
}

Creates a subprocess. If a block is specified, that block is run in the subprocess, and the subprocess terminates with a status of zero. Otherwise, the fork call returns twice, once in the parent, returning the process ID of the child, and once in the child, returning nil. The child process can exit using Kernel.exit! to avoid running any at_exit functions. The parent process should use Process.wait to collect the termination statuses of its children or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.

The thread calling fork is the only thread in the created child process. fork doesn't copy other threads.

If fork is not usable, Process.respond_to?(:fork) returns false.

static VALUE
rb_f_fork(VALUE obj)
{
    rb_pid_t pid;

    rb_secure(2);

    switch (pid = rb_fork_ruby(NULL)) {
      case 0:
        rb_thread_atfork();
        if (rb_block_given_p()) {
            int status;

            rb_protect(rb_yield, Qundef, &status);
            ruby_stop(status);
        }
        return Qnil;

      case -1:
        rb_sys_fail("fork(2)");
        return Qnil;

      default:
        return PIDT2NUM(pid);
    }
}

Returns the process group ID for the given process id. Not available on all platforms.

Process.getpgid(Process.ppid())   #=> 25527

static VALUE
proc_getpgid(VALUE obj, VALUE pid)
{
    rb_pid_t i;

    rb_secure(2);
    i = getpgid(NUM2PIDT(pid));
    if (i < 0) rb_sys_fail(0);
    return PIDT2NUM(i);
}

Returns the process group ID for this process. Not available on all platforms.

Process.getpgid(0)   #=> 25527
Process.getpgrp      #=> 25527

static VALUE
proc_getpgrp(void)
{
    rb_pid_t pgrp;

    rb_secure(2);
#if defined(HAVE_GETPGRP) && defined(GETPGRP_VOID)
    pgrp = getpgrp();
    if (pgrp < 0) rb_sys_fail(0);
    return PIDT2NUM(pgrp);
#else /* defined(HAVE_GETPGID) */
    pgrp = getpgid(0);
    if (pgrp < 0) rb_sys_fail(0);
    return PIDT2NUM(pgrp);
#endif
}

Gets the scheduling priority for specified process, process group, or user. kind indicates the kind of entity to find: one of Process::PRIO_PGRP, Process::PRIO_USER, or Process::PRIO_PROCESS. integer is an id indicating the particular process, process group, or user (an id of 0 means current). Lower priorities are more favorable for scheduling. Not available on all platforms.

Process.getpriority(Process::PRIO_USER, 0)      #=> 19
Process.getpriority(Process::PRIO_PROCESS, 0)   #=> 19

static VALUE
proc_getpriority(VALUE obj, VALUE which, VALUE who)
{
    int prio, iwhich, iwho;

    rb_secure(2);
    iwhich = NUM2INT(which);
    iwho   = NUM2INT(who);

    errno = 0;
    prio = getpriority(iwhich, iwho);
    if (errno) rb_sys_fail(0);
    return INT2FIX(prio);
}

Gets the resource limit of the process. cur_limit means current (soft) limit and max_limit means maximum (hard) limit.

resource indicates the kind of resource to limit. It is specified as a symbol such as :CORE, a string such as "CORE" or a constant such as Process::RLIMIT_CORE. See ::setrlimit for details.

cur_limit and max_limit may be Process::RLIM_INFINITY, Process::RLIM_SAVED_MAX or Process::RLIM_SAVED_CUR. See ::setrlimit and the system getrlimit(2) manual for details.

static VALUE
proc_getrlimit(VALUE obj, VALUE resource)
{
    struct rlimit rlim;

    rb_secure(2);

    if (getrlimit(rlimit_resource_type(resource), &rlim) < 0) {
        rb_sys_fail("getrlimit");
    }
    return rb_assoc_new(RLIM2NUM(rlim.rlim_cur), RLIM2NUM(rlim.rlim_max));
}

Returns the session ID for for the given process id. If not give, return current process sid. Not available on all platforms.

Process.getsid()                #=> 27422
Process.getsid(0)               #=> 27422
Process.getsid(Process.pid())   #=> 27422

static VALUE
proc_getsid(int argc, VALUE *argv)
{
    rb_pid_t sid;
    VALUE pid;

    rb_secure(2);
    rb_scan_args(argc, argv, "01", &pid);

    if (NIL_P(pid))
        pid = INT2NUM(0);

    sid = getsid(NUM2PIDT(pid));
    if (sid < 0) rb_sys_fail(0);
    return PIDT2NUM(sid);
}

Returns the (real) group ID for this process.

Process.gid   #=> 500

static VALUE
proc_getgid(VALUE obj)
{
    rb_gid_t gid = getgid();
    return GIDT2NUM(gid);
}

Sets the group ID for this process.

static VALUE
proc_setgid(VALUE obj, VALUE id)
{
    rb_gid_t gid;

    check_gid_switch();

    gid = OBJ2GID(id);
#if defined(HAVE_SETRESGID)
    if (setresgid(gid, -1, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREGID
    if (setregid(gid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETRGID
    if (setrgid(gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETGID
    {
        if (getegid() == gid) {
            if (setgid(gid) < 0) rb_sys_fail(0);
        }
        else {
            rb_notimplement();
        }
    }
#endif
    return GIDT2NUM(gid);
}

Get an Array of the gids of groups in the supplemental group access list for this process.

Process.groups   #=> [27, 6, 10, 11]

static VALUE
proc_getgroups(VALUE obj)
{
    VALUE ary, tmp;
    int i, ngroups;
    rb_gid_t *groups;

    ngroups = getgroups(0, NULL);
    if (ngroups == -1)
        rb_sys_fail(0);

    groups = ALLOCV_N(rb_gid_t, tmp, ngroups);

    ngroups = getgroups(ngroups, groups);
    if (ngroups == -1)
        rb_sys_fail(0);

    ary = rb_ary_new();
    for (i = 0; i < ngroups; i++)
        rb_ary_push(ary, GIDT2NUM(groups[i]));

    ALLOCV_END(tmp);

    return ary;
}

Set the supplemental group access list to the given Array of group IDs.

Process.groups   #=> [0, 1, 2, 3, 4, 6, 10, 11, 20, 26, 27]
Process.groups = [27, 6, 10, 11]   #=> [27, 6, 10, 11]
Process.groups   #=> [27, 6, 10, 11]

static VALUE
proc_setgroups(VALUE obj, VALUE ary)
{
    int ngroups, i;
    rb_gid_t *groups;
    VALUE tmp;
    PREPARE_GETGRNAM;

    Check_Type(ary, T_ARRAY);

    ngroups = RARRAY_LENINT(ary);
    if (ngroups > maxgroups())
        rb_raise(rb_eArgError, "too many groups, %d max", maxgroups());

    groups = ALLOCV_N(rb_gid_t, tmp, ngroups);

    for (i = 0; i < ngroups; i++) {
        VALUE g = RARRAY_PTR(ary)[i];

        groups[i] = OBJ2GID1(g);
    }
    FINISH_GETGRNAM;

    if (setgroups(ngroups, groups) == -1) /* ngroups <= maxgroups */
        rb_sys_fail(0);

    ALLOCV_END(tmp);

    return proc_getgroups(obj);
}

Initializes the supplemental group access list by reading the system group database and using all groups of which the given user is a member. The group with the specified gid is also added to the list. Returns the resulting Array of the gids of all the groups in the supplementary group access list. Not available on all platforms.

Process.groups   #=> [0, 1, 2, 3, 4, 6, 10, 11, 20, 26, 27]
Process.initgroups( "mgranger", 30 )   #=> [30, 6, 10, 11]
Process.groups   #=> [30, 6, 10, 11]

static VALUE
proc_initgroups(VALUE obj, VALUE uname, VALUE base_grp)
{
    if (initgroups(StringValuePtr(uname), OBJ2GID(base_grp)) != 0) {
        rb_sys_fail(0);
    }
    return proc_getgroups(obj);
}

Sends the given signal to the specified process id(s) if pid is positive. If pid is zero signal is sent to all processes whose group ID is equal to the group ID of the process. signal may be an integer signal number or a POSIX signal name (either with or without a SIG prefix). If signal is negative (or starts with a minus sign), kills process groups instead of processes. Not all signals are available on all platforms.

pid = fork do
   Signal.trap("HUP") { puts "Ouch!"; exit }
   # ... do some work ...
end
# ...
Process.kill("HUP", pid)
Process.wait

produces:

Ouch!

If signal is an integer but wrong for signal, Errno::EINVAL or RangeError will be raised. Otherwise unless signal is a String or a Symbol, and a known signal name, ArgumentError will be raised.

Also, Errno::ESRCH or RangeError for invalid pid, Errno::EPERM when failed because of no privilege, will be raised. In these cases, signals may have been sent to preceding processes.

VALUE
rb_f_kill(int argc, VALUE *argv)
{
#ifndef HAVE_KILLPG
#define killpg(pg, sig) kill(-(pg), (sig))
#endif
    int negative = 0;
    int sig;
    int i;
    volatile VALUE str;
    const char *s;

    rb_secure(2);
    rb_check_arity(argc, 2, UNLIMITED_ARGUMENTS);

    switch (TYPE(argv[0])) {
      case T_FIXNUM:
	sig = FIX2INT(argv[0]);
	break;

      case T_SYMBOL:
	s = rb_id2name(SYM2ID(argv[0]));
	if (!s) rb_raise(rb_eArgError, "bad signal");
	goto str_signal;

      case T_STRING:
	s = RSTRING_PTR(argv[0]);
      str_signal:
	if (s[0] == '-') {
	    negative++;
	    s++;
	}
	if (strncmp("SIG", s, 3) == 0)
	    s += 3;
	if ((sig = signm2signo(s)) == 0)
	    rb_raise(rb_eArgError, "unsupported name `SIG%s'", s);

	if (negative)
	    sig = -sig;
	break;

      default:
	str = rb_check_string_type(argv[0]);
	if (!NIL_P(str)) {
	    s = RSTRING_PTR(str);
	    goto str_signal;
	}
	rb_raise(rb_eArgError, "bad signal type %s",
		 rb_obj_classname(argv[0]));
	break;
    }

    if (sig < 0) {
	sig = -sig;
	for (i=1; i<argc; i++) {
	    if (killpg(NUM2PIDT(argv[i]), sig) < 0)
		rb_sys_fail(0);
	}
    }
    else {
	for (i=1; i<argc; i++) {
	    if (kill(NUM2PIDT(argv[i]), sig) < 0)
		rb_sys_fail(0);
	}
    }
    return INT2FIX(i-1);
}

Returns the maximum number of gids allowed in the supplemental group access list.

Process.maxgroups   #=> 32

static VALUE
proc_getmaxgroups(VALUE obj)
{
    return INT2FIX(maxgroups());
}

Sets the maximum number of gids allowed in the supplemental group access list.

static VALUE
proc_setmaxgroups(VALUE obj, VALUE val)
{
    int ngroups = FIX2INT(val);
    int ngroups_max = get_sc_ngroups_max();

    if (ngroups <= 0)
        rb_raise(rb_eArgError, "maxgroups %d shold be positive", ngroups);

    if (ngroups > RB_MAX_GROUPS)
        ngroups = RB_MAX_GROUPS;

    if (ngroups_max > 0 && ngroups > ngroups_max)
        ngroups = ngroups_max;

    _maxgroups = ngroups;

    return INT2FIX(_maxgroups);
}

Returns the process id of this process. Not available on all platforms.

Process.pid   #=> 27415

static VALUE
get_pid(void)
{
    rb_secure(2);
    return PIDT2NUM(getpid());
}

Returns the process id of the parent of this process. Returns untrustworthy value on Win32/64. Not available on all platforms.

puts "I am #{Process.pid}"
Process.fork { puts "Dad is #{Process.ppid}" }

produces:

I am 27417
Dad is 27417

static VALUE
get_ppid(void)
{
    rb_secure(2);
    return PIDT2NUM(getppid());
}

Sets the process group ID of pid (0 indicates this process) to integer. Not available on all platforms.

static VALUE
proc_setpgid(VALUE obj, VALUE pid, VALUE pgrp)
{
    rb_pid_t ipid, ipgrp;

    rb_secure(2);
    ipid = NUM2PIDT(pid);
    ipgrp = NUM2PIDT(pgrp);

    if (setpgid(ipid, ipgrp) < 0) rb_sys_fail(0);
    return INT2FIX(0);
}

Equivalent to setpgid(0,0). Not available on all platforms.

static VALUE
proc_setpgrp(void)
{
    rb_secure(2);
  /* check for posix setpgid() first; this matches the posix */
  /* getpgrp() above.  It appears that configure will set SETPGRP_VOID */
  /* even though setpgrp(0,0) would be preferred. The posix call avoids */
  /* this confusion. */
#ifdef HAVE_SETPGID
    if (setpgid(0,0) < 0) rb_sys_fail(0);
#elif defined(HAVE_SETPGRP) && defined(SETPGRP_VOID)
    if (setpgrp() < 0) rb_sys_fail(0);
#endif
    return INT2FIX(0);
}

See Process#getpriority.

Process.setpriority(Process::PRIO_USER, 0, 19)      #=> 0
Process.setpriority(Process::PRIO_PROCESS, 0, 19)   #=> 0
Process.getpriority(Process::PRIO_USER, 0)          #=> 19
Process.getpriority(Process::PRIO_PROCESS, 0)       #=> 19

static VALUE
proc_setpriority(VALUE obj, VALUE which, VALUE who, VALUE prio)
{
    int iwhich, iwho, iprio;

    rb_secure(2);
    iwhich = NUM2INT(which);
    iwho   = NUM2INT(who);
    iprio  = NUM2INT(prio);

    if (setpriority(iwhich, iwho, iprio) < 0)
        rb_sys_fail(0);
    return INT2FIX(0);
}

Sets the resource limit of the process. cur_limit means current (soft) limit and max_limit means maximum (hard) limit.

If max_limit is not given, cur_limit is used.

resource indicates the kind of resource to limit. It should be a symbol such as :CORE, a string such as "CORE" or a constant such as Process::RLIMIT_CORE. The available resources are OS dependent. Ruby may support following resources.

AS

total available memory (bytes) (SUSv3, NetBSD, FreeBSD, OpenBSD but 4.4BSD-Lite)

CORE

core size (bytes) (SUSv3)

CPU

CPU time (seconds) (SUSv3)

DATA

data segment (bytes) (SUSv3)

FSIZE

file size (bytes) (SUSv3)

MEMLOCK

total size for mlock(2) (bytes) (4.4BSD, GNU/Linux)

MSGQUEUE

allocation for POSIX message queues (bytes) (GNU/Linux)

NICE

ceiling on process's nice(2) value (number) (GNU/Linux)

NOFILE

file descriptors (number) (SUSv3)

NPROC

number of processes for the user (number) (4.4BSD, GNU/Linux)

RSS

resident memory size (bytes) (4.2BSD, GNU/Linux)

RTPRIO

ceiling on the process's real-time priority (number) (GNU/Linux)

RTTIME

CPU time for real-time process (us) (GNU/Linux)

SBSIZE

all socket buffers (bytes) (NetBSD, FreeBSD)

SIGPENDING

number of queued signals allowed (signals) (GNU/Linux)

STACK

stack size (bytes) (SUSv3)

cur_limit and max_limit may be :INFINITY, "INFINITY" or Process::RLIM_INFINITY, which means that the resource is not limited. They may be Process::RLIM_SAVED_MAX, Process::RLIM_SAVED_CUR and corresponding symbols and strings too. See system setrlimit(2) manual for details.

The following example raises the soft limit of core size to the hard limit to try to make core dump possible.

Process.setrlimit(:CORE, Process.getrlimit(:CORE)[1])

static VALUE
proc_setrlimit(int argc, VALUE *argv, VALUE obj)
{
    VALUE resource, rlim_cur, rlim_max;
    struct rlimit rlim;

    rb_secure(2);

    rb_scan_args(argc, argv, "21", &resource, &rlim_cur, &rlim_max);
    if (rlim_max == Qnil)
        rlim_max = rlim_cur;

    rlim.rlim_cur = rlimit_resource_value(rlim_cur);
    rlim.rlim_max = rlimit_resource_value(rlim_max);

    if (setrlimit(rlimit_resource_type(resource), &rlim) < 0) {
        rb_sys_fail("setrlimit");
    }
    return Qnil;
}

Establishes this process as a new session and process group leader, with no controlling tty. Returns the session id. Not available on all platforms.

Process.setsid   #=> 27422

static VALUE
proc_setsid(void)
{
    rb_pid_t pid;

    rb_secure(2);
    pid = setsid();
    if (pid < 0) rb_sys_fail(0);
    return PIDT2NUM(pid);
}

spawn executes specified command and return its pid.

This method doesn't wait for end of the command. The parent process should use Process.wait to collect the termination status of its child or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.

spawn has bunch of options to specify process attributes:

env: hash
  name => val : set the environment variable
  name => nil : unset the environment variable
command...:
  commandline                 : command line string which is passed to the standard shell
  cmdname, arg1, ...          : command name and one or more arguments (no shell)
  [cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
options: hash
  clearing environment variables:
    :unsetenv_others => true   : clear environment variables except specified by env
    :unsetenv_others => false  : don't clear (default)
  process group:
    :pgroup => true or 0 : make a new process group
    :pgroup => pgid      : join to specified process group
    :pgroup => nil       : don't change the process group (default)
  create new process group: Windows only
    :new_pgroup => true  : the new process is the root process of a new process group
    :new_pgroup => false : don't create a new process group (default)
  resource limit: resourcename is core, cpu, data, etc.  See Process.setrlimit.
    :rlimit_resourcename => limit
    :rlimit_resourcename => [cur_limit, max_limit]
  umask:
    :umask => int
  redirection:
    key:
      FD              : single file descriptor in child process
      [FD, FD, ...]   : multiple file descriptor in child process
    value:
      FD                        : redirect to the file descriptor in parent process
      string                    : redirect to file with open(string, "r" or "w")
      [string]                  : redirect to file with open(string, File::RDONLY)
      [string, open_mode]       : redirect to file with open(string, open_mode, 0644)
      [string, open_mode, perm] : redirect to file with open(string, open_mode, perm)
      [:child, FD]              : redirect to the redirected file descriptor
      :close                    : close the file descriptor in child process
    FD is one of follows
      :in     : the file descriptor 0 which is the standard input
      :out    : the file descriptor 1 which is the standard output
      :err    : the file descriptor 2 which is the standard error
      integer : the file descriptor of specified the integer
      io      : the file descriptor specified as io.fileno
  file descriptor inheritance: close non-redirected non-standard fds (3, 4, 5, ...) or not
    :close_others => true  : don't inherit
  current directory:
    :chdir => str

If a hash is given as env, the environment is updated by env before exec(2) in the child process. If a pair in env has nil as the value, the variable is deleted.

# set FOO as BAR and unset BAZ.
pid = spawn({"FOO"=>"BAR", "BAZ"=>nil}, command)

If a hash is given as options, it specifies process group, create new process group, resource limit, current directory, umask and redirects for the child process. Also, it can be specified to clear environment variables.

The :unsetenv_others key in options specifies to clear environment variables, other than specified by env.

pid = spawn(command, :unsetenv_others=>true) # no environment variable
pid = spawn({"FOO"=>"BAR"}, command, :unsetenv_others=>true) # FOO only

The :pgroup key in options specifies a process group. The corresponding value should be true, zero or positive integer. true and zero means the process should be a process leader of a new process group. Other values specifies a process group to be belongs.

pid = spawn(command, :pgroup=>true) # process leader
pid = spawn(command, :pgroup=>10) # belongs to the process group 10

The :new_pgroup key in options specifies to pass CREATE_NEW_PROCESS_GROUP flag to CreateProcessW() that is Windows API. This option is only for Windows. true means the new process is the root process of the new process group. The new process has CTRL+C disabled. This flag is necessary for Process.kill(:SIGINT, pid) on the subprocess. :new_pgroup is false by default.

pid = spawn(command, :new_pgroup=>true)  # new process group
pid = spawn(command, :new_pgroup=>false) # same process group

The :rlimit_foo key specifies a resource limit. foo should be one of resource types such as core. The corresponding value should be an integer or an array which have one or two integers: same as cur_limit and max_limit arguments for ::setrlimit.

cur, max = Process.getrlimit(:CORE)
pid = spawn(command, :rlimit_core=>[0,max]) # disable core temporary.
pid = spawn(command, :rlimit_core=>max) # enable core dump
pid = spawn(command, :rlimit_core=>0) # never dump core.

The :umask key in options specifies the umask.

pid = spawn(command, :umask=>077)

The :in, :out, :err, a fixnum, an IO and an array key specifies a redirection. The redirection maps a file descriptor in the child process.

For example, stderr can be merged into stdout as follows:

pid = spawn(command, :err=>:out)
pid = spawn(command, 2=>1)
pid = spawn(command, STDERR=>:out)
pid = spawn(command, STDERR=>STDOUT)

The hash keys specifies a file descriptor in the child process started by spawn. :err, 2 and STDERR specifies the standard error stream (stderr).

The hash values specifies a file descriptor in the parent process which invokes spawn. :out, 1 and STDOUT specifies the standard output stream (stdout).

In the above example, the standard output in the child process is not specified. So it is inherited from the parent process.

The standard input stream (stdin) can be specified by :in, 0 and STDIN.

A filename can be specified as a hash value.

pid = spawn(command, :in=>"/dev/null") # read mode
pid = spawn(command, :out=>"/dev/null") # write mode
pid = spawn(command, :err=>"log") # write mode
pid = spawn(command, 3=>"/dev/null") # read mode

For stdout and stderr, it is opened in write mode. Otherwise read mode is used.

For specifying flags and permission of file creation explicitly, an array is used instead.

pid = spawn(command, :in=>["file"]) # read mode is assumed
pid = spawn(command, :in=>["file", "r"])
pid = spawn(command, :out=>["log", "w"]) # 0644 assumed
pid = spawn(command, :out=>["log", "w", 0600])
pid = spawn(command, :out=>["log", File::WRONLY|File::EXCL|File::CREAT, 0600])

The array specifies a filename, flags and permission. The flags can be a string or an integer. If the flags is omitted or nil, File::RDONLY is assumed. The permission should be an integer. If the permission is omitted or nil, 0644 is assumed.

If an array of IOs and integers are specified as a hash key, all the elements are redirected.

# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, [:out, :err]=>["log", "w"])

Another way to merge multiple file descriptors is [:child, fd]. [:child, fd] means the file descriptor in the child process. This is different from fd. For example, :err=>:out means redirecting child stderr to parent stdout. But :err=>[:child, :out] means redirecting child stderr to child stdout. They differ if stdout is redirected in the child process as follows.

# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, :out=>["log", "w"], :err=>[:child, :out])

[:child, :out] can be used to merge stderr into stdout in IO.popen. In this case, IO.popen redirects stdout to a pipe in the child process and [:child, :out] refers the redirected stdout.

io = IO.popen(["sh", "-c", "echo out; echo err >&2", :err=>[:child, :out]])
p io.read #=> "out\nerr\n"

The :chdir key in options specifies the current directory.

pid = spawn(command, :chdir=>"/var/tmp")

spawn closes all non-standard unspecified descriptors by default. The “standard” descriptors are 0, 1 and 2. This behavior is specified by :close_others option. :close_others doesn't affect the standard descriptors which are closed only if :close is specified explicitly.

pid = spawn(command, :close_others=>true)  # close 3,4,5,... (default)
pid = spawn(command, :close_others=>false) # don't close 3,4,5,...

:close_others is true by default for spawn and IO.popen.

Note that fds which close-on-exec flag is already set are closed regardless of :close_others option.

So IO.pipe and spawn can be used as IO.popen.

# similar to r = IO.popen(command)
r, w = IO.pipe
pid = spawn(command, :out=>w)   # r, w is closed in the child process.
w.close

:close is specified as a hash value to close a fd individually.

f = open(foo)
system(command, f=>:close)        # don't inherit f.

If a file descriptor need to be inherited, io=>io can be used.

# valgrind has --log-fd option for log destination.
# log_w=>log_w indicates log_w.fileno inherits to child process.
log_r, log_w = IO.pipe
pid = spawn("valgrind", "--log-fd=#{log_w.fileno}", "echo", "a", log_w=>log_w)
log_w.close
p log_r.read

It is also possible to exchange file descriptors.

pid = spawn(command, :out=>:err, :err=>:out)

The hash keys specify file descriptors in the child process. The hash values specifies file descriptors in the parent process. So the above specifies exchanging stdout and stderr. Internally, spawn uses an extra file descriptor to resolve such cyclic file descriptor mapping.

See Kernel.exec for the standard shell.

static VALUE
rb_f_spawn(int argc, VALUE *argv)
{
    rb_pid_t pid;
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };
    VALUE execarg_obj, fail_str;
    struct rb_execarg *eargp;

    execarg_obj = rb_execarg_new(argc, argv, TRUE);
    eargp = rb_execarg_get(execarg_obj);
    rb_execarg_fixup(execarg_obj);
    fail_str = eargp->use_shell ? eargp->invoke.sh.shell_script : eargp->invoke.cmd.command_name;

    pid = rb_spawn_process(eargp, errmsg, sizeof(errmsg));
    RB_GC_GUARD(execarg_obj);

    if (pid == -1) {
        const char *prog = errmsg;
        if (!prog[0]) {
            rb_sys_fail_str(fail_str);
        }
        rb_sys_fail(prog);
    }
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    return PIDT2NUM(pid);
#else
    return Qnil;
#endif
}

Returns a Tms structure (see Struct::Tms) that contains user and system CPU times for this process, and also for children processes.

t = Process.times
[ t.utime, t.stime, t.cutime, t.cstime ]   #=> [0.0, 0.02, 0.00, 0.00]

VALUE
rb_proc_times(VALUE obj)
{
    const double hertz =
#ifdef HAVE__SC_CLK_TCK
        (double)sysconf(_SC_CLK_TCK);
#else
#ifndef HZ
# ifdef CLK_TCK
#   define HZ CLK_TCK
# else
#   define HZ 60
# endif
#endif /* HZ */
        HZ;
#endif
    struct tms buf;
    volatile VALUE utime, stime, cutime, sctime;

    times(&buf);
    return rb_struct_new(rb_cProcessTms,
                         utime = DBL2NUM(buf.tms_utime / hertz),
                         stime = DBL2NUM(buf.tms_stime / hertz),
                         cutime = DBL2NUM(buf.tms_cutime / hertz),
                         sctime = DBL2NUM(buf.tms_cstime / hertz));
}

Returns the (real) user ID of this process.

Process.uid   #=> 501

static VALUE
proc_getuid(VALUE obj)
{
    rb_uid_t uid = getuid();
    return UIDT2NUM(uid);
}

Sets the (user) user ID for this process. Not available on all platforms.

static VALUE
proc_setuid(VALUE obj, VALUE id)
{
    rb_uid_t uid;

    check_uid_switch();

    uid = OBJ2UID(id);
#if defined(HAVE_SETRESUID)
    if (setresuid(uid, -1, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREUID
    if (setreuid(uid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETRUID
    if (setruid(uid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETUID
    {
        if (geteuid() == uid) {
            if (setuid(uid) < 0) rb_sys_fail(0);
        }
        else {
            rb_notimplement();
        }
    }
#endif
    return id;
}

Waits for a child process to exit, returns its process id, and sets $? to a Process::Status object containing information on that process. Which child it waits on depends on the value of pid:

> 0

Waits for the child whose process ID equals pid.

0

Waits for any child whose process group ID equals that of the calling process.

-1

Waits for any child process (the default if no pid is given).

< -1

Waits for any child whose process group ID equals the absolute value of pid.

The flags argument may be a logical or of the flag values Process::WNOHANG (do not block if no child available) or Process::WUNTRACED (return stopped children that haven't been reported). Not all flags are available on all platforms, but a flag value of zero will work on all platforms.

Calling this method raises a SystemCallError if there are no child processes. Not available on all platforms.

include Process
fork { exit 99 }                 #=> 27429
wait                             #=> 27429
$?.exitstatus                    #=> 99

pid = fork { sleep 3 }           #=> 27440
Time.now                         #=> 2008-03-08 19:56:16 +0900
waitpid(pid, Process::WNOHANG)   #=> nil
Time.now                         #=> 2008-03-08 19:56:16 +0900
waitpid(pid, 0)                  #=> 27440
Time.now                         #=> 2008-03-08 19:56:19 +0900

static VALUE
proc_wait(int argc, VALUE *argv)
{
    VALUE vpid, vflags;
    rb_pid_t pid;
    int flags, status;

    rb_secure(2);
    flags = 0;
    if (argc == 0) {
        pid = -1;
    }
    else {
        rb_scan_args(argc, argv, "02", &vpid, &vflags);
        pid = NUM2PIDT(vpid);
        if (argc == 2 && !NIL_P(vflags)) {
            flags = NUM2UINT(vflags);
        }
    }
    if ((pid = rb_waitpid(pid, &status, flags)) < 0)
        rb_sys_fail(0);
    if (pid == 0) {
        rb_last_status_clear();
        return Qnil;
    }
    return PIDT2NUM(pid);
}

Waits for a child process to exit (see ::waitpid for exact semantics) and returns an array containing the process id and the exit status (a Process::Status object) of that child. Raises a SystemCallError if there are no child processes.

Process.fork { exit 99 }   #=> 27437
pid, status = Process.wait2
pid                        #=> 27437
status.exitstatus          #=> 99

static VALUE
proc_wait2(int argc, VALUE *argv)
{
    VALUE pid = proc_wait(argc, argv);
    if (NIL_P(pid)) return Qnil;
    return rb_assoc_new(pid, rb_last_status_get());
}

Waits for all children, returning an array of pid/status pairs (where status is a Process::Status object).

fork { sleep 0.2; exit 2 }   #=> 27432
fork { sleep 0.1; exit 1 }   #=> 27433
fork {            exit 0 }   #=> 27434
p Process.waitall

produces:

[[30982, #<Process::Status: pid 30982 exit 0>],
 [30979, #<Process::Status: pid 30979 exit 1>],
 [30976, #<Process::Status: pid 30976 exit 2>]]

static VALUE
proc_waitall(void)
{
    VALUE result;
    rb_pid_t pid;
    int status;

    rb_secure(2);
    result = rb_ary_new();
#ifdef NO_WAITPID
    if (pid_tbl) {
        st_foreach(pid_tbl, waitall_each, result);
    }
#else
    rb_last_status_clear();
#endif

    for (pid = -1;;) {
#ifdef NO_WAITPID
        pid = wait(&status);
#else
        pid = rb_waitpid(-1, &status, 0);
#endif
        if (pid == -1) {
            if (errno == ECHILD)
                break;
#ifdef NO_WAITPID
            if (errno == EINTR) {
                rb_thread_schedule();
                continue;
            }
#endif
            rb_sys_fail(0);
        }
#ifdef NO_WAITPID
        rb_last_status_set(status, pid);
#endif
        rb_ary_push(result, rb_assoc_new(PIDT2NUM(pid), rb_last_status_get()));
    }
    return result;
}

Waits for a child process to exit, returns its process id, and sets $? to a Process::Status object containing information on that process. Which child it waits on depends on the value of pid:

> 0

Waits for the child whose process ID equals pid.

0

Waits for any child whose process group ID equals that of the calling process.

-1

Waits for any child process (the default if no pid is given).

< -1

Waits for any child whose process group ID equals the absolute value of pid.

The flags argument may be a logical or of the flag values Process::WNOHANG (do not block if no child available) or Process::WUNTRACED (return stopped children that haven't been reported). Not all flags are available on all platforms, but a flag value of zero will work on all platforms.

Calling this method raises a SystemCallError if there are no child processes. Not available on all platforms.

include Process
fork { exit 99 }                 #=> 27429
wait                             #=> 27429
$?.exitstatus                    #=> 99

pid = fork { sleep 3 }           #=> 27440
Time.now                         #=> 2008-03-08 19:56:16 +0900
waitpid(pid, Process::WNOHANG)   #=> nil
Time.now                         #=> 2008-03-08 19:56:16 +0900
waitpid(pid, 0)                  #=> 27440
Time.now                         #=> 2008-03-08 19:56:19 +0900

static VALUE
proc_wait(int argc, VALUE *argv)
{
    VALUE vpid, vflags;
    rb_pid_t pid;
    int flags, status;

    rb_secure(2);
    flags = 0;
    if (argc == 0) {
        pid = -1;
    }
    else {
        rb_scan_args(argc, argv, "02", &vpid, &vflags);
        pid = NUM2PIDT(vpid);
        if (argc == 2 && !NIL_P(vflags)) {
            flags = NUM2UINT(vflags);
        }
    }
    if ((pid = rb_waitpid(pid, &status, flags)) < 0)
        rb_sys_fail(0);
    if (pid == 0) {
        rb_last_status_clear();
        return Qnil;
    }
    return PIDT2NUM(pid);
}

Waits for a child process to exit (see ::waitpid for exact semantics) and returns an array containing the process id and the exit status (a Process::Status object) of that child. Raises a SystemCallError if there are no child processes.

Process.fork { exit 99 }   #=> 27437
pid, status = Process.wait2
pid                        #=> 27437
status.exitstatus          #=> 99

static VALUE
proc_wait2(int argc, VALUE *argv)
{
    VALUE pid = proc_wait(argc, argv);
    if (NIL_P(pid)) return Qnil;
    return rb_assoc_new(pid, rb_last_status_get());
}