Process

Module

The Process module is a collection of methods used to manipulate processes.

Constants

WNOHANG

see Process.wait

WUNTRACED

see Process.wait

PRIO_PROCESS

see Process.setpriority

PRIO_PGRP

see Process.setpriority

PRIO_USER

see Process.setpriority

RLIM_SAVED_MAX

see Process.setrlimit

RLIM_INFINITY

see Process.setrlimit

RLIM_SAVED_CUR

see Process.setrlimit

RLIMIT_AS

Maximum size of the process’s virtual memory (address space) in bytes.

see the system getrlimit(2) manual for details.

RLIMIT_CORE

Maximum size of the core file.

see the system getrlimit(2) manual for details.

RLIMIT_CPU

CPU time limit in seconds.

see the system getrlimit(2) manual for details.

RLIMIT_DATA

Maximum size of the process’s data segment.

see the system getrlimit(2) manual for details.

RLIMIT_FSIZE

Maximum size of files that the process may create.

see the system getrlimit(2) manual for details.

RLIMIT_MEMLOCK

Maximum number of bytes of memory that may be locked into RAM.

see the system getrlimit(2) manual for details.

RLIMIT_MSGQUEUE

Specifies the limit on the number of bytes that can be allocated for POSIX message queues for the real user ID of the calling process.

see the system getrlimit(2) manual for details.

RLIMIT_NICE

Specifies a ceiling to which the process’s nice value can be raised.

see the system getrlimit(2) manual for details.

RLIMIT_NOFILE

Specifies a value one greater than the maximum file descriptor number that can be opened by this process.

see the system getrlimit(2) manual for details.

RLIMIT_NPROC

The maximum number of processes that can be created for the real user ID of the calling process.

see the system getrlimit(2) manual for details.

RLIMIT_RSS

Specifies the limit (in pages) of the process’s resident set.

see the system getrlimit(2) manual for details.

RLIMIT_RTPRIO

Specifies a ceiling on the real-time priority that may be set for this process.

see the system getrlimit(2) manual for details.

RLIMIT_RTTIME

Specifies limit on CPU time this process scheduled under a real-time scheduling policy can consume.

see the system getrlimit(2) manual for details.

RLIMIT_SBSIZE

Maximum size of the socket buffer.

RLIMIT_SIGPENDING

Specifies a limit on the number of signals that may be queued for the real user ID of the calling process.

see the system getrlimit(2) manual for details.

RLIMIT_STACK

Maximum size of the stack, in bytes.

see the system getrlimit(2) manual for details.

CLOCK_REALTIME

see Process.clock_gettime

CLOCK_MONOTONIC

see Process.clock_gettime

CLOCK_PROCESS_CPUTIME_ID

see Process.clock_gettime

CLOCK_THREAD_CPUTIME_ID

see Process.clock_gettime

CLOCK_VIRTUAL

see Process.clock_gettime

CLOCK_PROF

see Process.clock_gettime

CLOCK_REALTIME_FAST

see Process.clock_gettime

CLOCK_REALTIME_PRECISE

see Process.clock_gettime

CLOCK_REALTIME_COARSE

see Process.clock_gettime

CLOCK_REALTIME_ALARM

see Process.clock_gettime

CLOCK_MONOTONIC_FAST

see Process.clock_gettime

CLOCK_MONOTONIC_PRECISE

see Process.clock_gettime

CLOCK_MONOTONIC_RAW

see Process.clock_gettime

CLOCK_MONOTONIC_RAW_APPROX

see Process.clock_gettime

CLOCK_MONOTONIC_COARSE

see Process.clock_gettime

CLOCK_BOOTTIME

see Process.clock_gettime

CLOCK_BOOTTIME_ALARM

see Process.clock_gettime

CLOCK_UPTIME

see Process.clock_gettime

CLOCK_UPTIME_FAST

see Process.clock_gettime

CLOCK_UPTIME_PRECISE

see Process.clock_gettime

CLOCK_UPTIME_RAW

see Process.clock_gettime

CLOCK_UPTIME_RAW_APPROX

see Process.clock_gettime

CLOCK_SECOND

see Process.clock_gettime

CLOCK_TAI

see Process.clock_gettime

Class Methods

abort

Kernel::abort([msg])

Process.abort([msg])
::

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

Process.argv0 → frozen_string
::

Returns the name of the script being executed. The value is not affected by assigning a new value to $0.

This method first appeared in Ruby 2.1 to serve as a global variable free means to get the script name.

Process.clock_getres(clock_id [, unit]) → number
::

Returns an estimate of the resolution of a clock_id using the POSIX clock_getres() function.

Note the reported resolution is often inaccurate on most platforms due to underlying bugs for this function and therefore the reported resolution often differs from the actual resolution of the clock in practice. Inaccurate reported resolutions have been observed for various clocks including CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW when using Linux, macOS, BSD or AIX platforms, when using ARM processors, or when using virtualization.

clock_id specifies a kind of clock. See the document of Process.clock_gettime for details. clock_id can be a symbol as for Process.clock_gettime.

If the given clock_id is not supported, Errno::EINVAL is raised.

unit specifies the type of the return value. Process.clock_getres accepts unit as Process.clock_gettime. The default value, :float_second, is also the same as Process.clock_gettime.

Process.clock_getres also accepts :hertz as unit. :hertz means the reciprocal of :float_second.

:hertz can be used to obtain the exact value of the clock ticks per second for the times() function and CLOCKS_PER_SEC for the clock() function.

Process.clock_getres(:TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID, :hertz) returns the clock ticks per second.

Process.clock_getres(:CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID, :hertz) returns CLOCKS_PER_SEC.

p Process.clock_getres(Process::CLOCK_MONOTONIC)
#=> 1.0e-09

Process.clock_gettime(clock_id [, unit]) → number
::

Returns a time returned by POSIX clock_gettime() function.

p Process.clock_gettime(Process::CLOCK_MONOTONIC)
#=> 896053.968060096

clock_id specifies a kind of clock. It is specified as a constant which begins with Process::CLOCK_ such as Process::CLOCK_REALTIME and Process::CLOCK_MONOTONIC.

The supported constants depends on OS and version. Ruby provides following types of clock_id if available.

CLOCK_REALTIME

SUSv2 to 4, Linux 2.5.63, FreeBSD 3.0, NetBSD 2.0, OpenBSD 2.1, macOS 10.12

CLOCK_MONOTONIC

SUSv3 to 4, Linux 2.5.63, FreeBSD 3.0, NetBSD 2.0, OpenBSD 3.4, macOS 10.12

CLOCK_PROCESS_CPUTIME_ID

SUSv3 to 4, Linux 2.5.63, FreeBSD 9.3, OpenBSD 5.4, macOS 10.12

CLOCK_THREAD_CPUTIME_ID

SUSv3 to 4, Linux 2.5.63, FreeBSD 7.1, OpenBSD 5.4, macOS 10.12

CLOCK_VIRTUAL

FreeBSD 3.0, OpenBSD 2.1

CLOCK_PROF

FreeBSD 3.0, OpenBSD 2.1

CLOCK_REALTIME_FAST

FreeBSD 8.1

CLOCK_REALTIME_PRECISE

FreeBSD 8.1

CLOCK_REALTIME_COARSE

Linux 2.6.32

CLOCK_REALTIME_ALARM

Linux 3.0

CLOCK_MONOTONIC_FAST

FreeBSD 8.1

CLOCK_MONOTONIC_PRECISE

FreeBSD 8.1

CLOCK_MONOTONIC_COARSE

Linux 2.6.32

CLOCK_MONOTONIC_RAW

Linux 2.6.28, macOS 10.12

CLOCK_MONOTONIC_RAW_APPROX

macOS 10.12

CLOCK_BOOTTIME

Linux 2.6.39

CLOCK_BOOTTIME_ALARM

Linux 3.0

CLOCK_UPTIME

FreeBSD 7.0, OpenBSD 5.5

CLOCK_UPTIME_FAST

FreeBSD 8.1

CLOCK_UPTIME_RAW

macOS 10.12

CLOCK_UPTIME_RAW_APPROX

macOS 10.12

CLOCK_UPTIME_PRECISE

FreeBSD 8.1

CLOCK_SECOND

FreeBSD 8.1

CLOCK_TAI

Linux 3.10

Note that SUS stands for Single Unix Specification. SUS contains POSIX and clock_gettime is defined in the POSIX part. SUS defines CLOCK_REALTIME mandatory but CLOCK_MONOTONIC, CLOCK_PROCESS_CPUTIME_ID and CLOCK_THREAD_CPUTIME_ID are optional.

Also, several symbols are accepted as clock_id. There are emulations for clock_gettime().

For example, Process::CLOCK_REALTIME is defined as :GETTIMEOFDAY_BASED_CLOCK_REALTIME when clock_gettime() is not available.

Emulations for CLOCK_REALTIME:

:GETTIMEOFDAY_BASED_CLOCK_REALTIME

Use gettimeofday() defined by SUS. (SUSv4 obsoleted it, though.) The resolution is 1 microsecond.

:TIME_BASED_CLOCK_REALTIME

Use time() defined by ISO C. The resolution is 1 second.

Emulations for CLOCK_MONOTONIC:

:MACH_ABSOLUTE_TIME_BASED_CLOCK_MONOTONIC

Use mach_absolute_time(), available on Darwin. The resolution is CPU dependent.

:TIMES_BASED_CLOCK_MONOTONIC

Use the result value of times() defined by POSIX. POSIX defines it as “times() shall return the elapsed real time, in clock ticks, since an arbitrary point in the past (for example, system start-up time)”. For example, GNU/Linux returns a value based on jiffies and it is monotonic. However, 4.4BSD uses gettimeofday() and it is not monotonic. (FreeBSD uses clock_gettime(CLOCK_MONOTONIC) instead, though.) The resolution is the clock tick. “getconf CLK_TCK” command shows the clock ticks per second. (The clock ticks per second is defined by HZ macro in older systems.) If it is 100 and clock_t is 32 bits integer type, the resolution is 10 millisecond and cannot represent over 497 days.

Emulations for CLOCK_PROCESS_CPUTIME_ID:

:GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID

Use getrusage() defined by SUS. getrusage() is used with RUSAGE_SELF to obtain the time only for the calling process (excluding the time for child processes). The result is addition of user time (ru_utime) and system time (ru_stime). The resolution is 1 microsecond.

:TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID

Use times() defined by POSIX. The result is addition of user time (tms_utime) and system time (tms_stime). tms_cutime and tms_cstime are ignored to exclude the time for child processes. The resolution is the clock tick. “getconf CLK_TCK” command shows the clock ticks per second. (The clock ticks per second is defined by HZ macro in older systems.) If it is 100, the resolution is 10 millisecond.

:CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID

Use clock() defined by ISO C. The resolution is 1/CLOCKS_PER_SEC. CLOCKS_PER_SEC is the C-level macro defined by time.h. SUS defines CLOCKS_PER_SEC is 1000000. Non-Unix systems may define it a different value, though. If CLOCKS_PER_SEC is 1000000 as SUS, the resolution is 1 microsecond. If CLOCKS_PER_SEC is 1000000 and clock_t is 32 bits integer type, it cannot represent over 72 minutes.

If the given clock_id is not supported, Errno::EINVAL is raised.

unit specifies a type of the return value.

:float_second

number of seconds as a float (default)

:float_millisecond

number of milliseconds as a float

:float_microsecond

number of microseconds as a float

:second

number of seconds as an integer

:millisecond

number of milliseconds as an integer

:microsecond

number of microseconds as an integer

:nanosecond

number of nanoseconds as an integer

The underlying function, clock_gettime(), returns a number of nanoseconds. Float object (IEEE 754 double) is not enough to represent the return value for CLOCK_REALTIME. If the exact nanoseconds value is required, use :nanoseconds as the unit.

The origin (zero) of the returned value varies. For example, system start up time, process start up time, the Epoch, etc.

The origin in CLOCK_REALTIME is defined as the Epoch (1970-01-01 00:00:00 UTC). But some systems count leap seconds and others doesn’t. So the result can be interpreted differently across systems. Time.now is recommended over CLOCK_REALTIME.

Process.daemon() → 0

Process.daemon(nochdir=nil,noclose=nil) → 0
::

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::*.

Process.detach(pid) → thread
::

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 intend 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)

Process.egid → integer

Process::GID.eid → integer

Process::Sys.geteid → integer
::

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

Process.egid   #=> 500

Process.egid = integer → integer
::

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

Process.euid → integer

Process::UID.eid → integer

Process::Sys.geteuid → integer
::

Returns the effective user ID for this process.

Process.euid   #=> 501

Process.euid= user
::

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

exec([env,] command... [,options])
::

Replaces the current process by running the given external command, which can take one of the following forms:

exec(commandline)

command line string which is passed to the standard shell

exec(cmdname, arg1, ...)

command name and one or more arguments (no shell)

exec([cmdname, argv0], arg1, ...)

command name, argv and zero or more arguments (no shell)

In the first form, the string is taken as a command line that is subject to shell expansion before being executed.

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

If the string from the first form (exec("command")) follows these simple rules:

  • no meta characters

  • no shell reserved word and no special built-in

  • Ruby invokes the command directly without shell

You can force shell invocation by adding “;” to the string (because “;” is a meta character).

Note that this behavior is observable by pid obtained (return value of spawn() and IO#pid for IO.popen) is the pid of the invoked command, not shell.

In the second form (exec("command1", "arg1", ...)), the first is taken as a command name and the rest are passed as parameters to command with no shell expansion.

In the third form (exec(["command", "argv0"], "arg1", ...)), starting 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 are used, so the running command may inherit some of the environment of the original program (including open file descriptors).

This behavior is modified by the given env and options parameters. See ::spawn for details.

If the command fails to execute (typically Errno::ENOENT when it was not found) a SystemCallError exception is raised.

This method modifies process attributes according to given options before exec(2) system call. See ::spawn for more details about the given options.

The modified attributes may be retained when exec(2) system call fails.

For example, hard resource limits are not restorable.

Consider to create a child process using ::spawn or Kernel#system if this is not acceptable.

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

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

exit(status=true)

Kernel::exit(status=true)

Process::exit(status=true)
::

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

Process.exit!(status=false)
::

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

Process.exit!(true)

Kernel.fork [{ block }] → integer or nil

Process.fork [{ block }] → integer or nil
::

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.

Note that fork(2) is not available on some platforms like Windows and NetBSD 4. Therefore you should use spawn() instead of fork().

Process.getpgid(pid) → integer
::

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

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

Process.getpgrp → integer
::

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

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

Process.getpriority(kind, integer) → integer
::

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

Process.getrlimit(resource) → [cur_limit, max_limit]
::

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 Process.setrlimit for details.

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

Process.getsid() → integer

Process.getsid(pid) → integer
::

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

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

Process.gid → integer

Process::GID.rid → integer

Process::Sys.getgid → integer
::

Returns the (real) group ID for this process.

Process.gid   #=> 500

Process.gid= integer → integer
::

Sets the group ID for this process.

Process.groups → array
::

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

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

Note that this method is just a wrapper of getgroups(2). This means that the following characteristics of the result completely depend on your system:

  • the result is sorted

  • the result includes effective GIDs

  • the result does not include duplicated GIDs

You can make sure to get a sorted unique GID list of the current process by this expression:

Process.groups.uniq.sort

Process.groups= array → array
::

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]

Process.initgroups(username, gid) → array
::

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]

Process.kill(signal, pid, ...) → integer
::

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. If pid is negative, results are dependent on the operating system. 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. The keys and values of Signal.list are known signal names and numbers, respectively.

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.

Process.last_status → Process::Status or nil
::

Returns the status of the last executed child process in the current thread.

Process.wait Process.spawn("ruby", "-e", "exit 13")
Process.last_status   #=> #<Process::Status: pid 4825 exit 13>

If no child process has ever been executed in the current thread, this returns nil.

Process.last_status   #=> nil

Process.maxgroups → integer
::

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

Process.maxgroups   #=> 32

Process.maxgroups= integer → integer
::

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

Process.pid → integer
::

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

Process.pid   #=> 27415

Process.ppid → integer
::

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

Process.setpgid(pid, integer) → 0
::

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

Process.setpgrp → 0
::

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

Process.setpriority(kind, integer, priority) → 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

Process.setproctitle(string) → string
::

Sets the process title that appears on the ps(1) command. Not necessarily effective on all platforms. No exception will be raised regardless of the result, nor will NotImplementedError be raised even if the platform does not support the feature.

Calling this method does not affect the value of $0.

Process.setproctitle('myapp: worker #%d' % worker_id)

This method first appeared in Ruby 2.1 to serve as a global variable free means to change the process title.

Process.setrlimit(resource, cur_limit, max_limit) → nil

Process.setrlimit(resource, cur_limit) → nil
::

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])

Process.setsid → integer
::

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

spawn([env,] command... [,options]) → pid

Process.spawn([env,] command... [,options]) → pid
::

spawn executes specified command and return its pid.

pid = spawn("tar xf ruby-2.0.0-p195.tar.bz2")
Process.wait pid

pid = spawn(RbConfig.ruby, "-eputs'Hello, world!'")
Process.wait pid

This method is similar to Kernel#system but it doesn’t wait for the command to finish.

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

  the keys and the values except for +nil+ must be strings.
command...:
  commandline                 : command line string which is passed to the standard shell
  cmdname, arg1, ...          : command name and one or more arguments (This form does not use the shell. See below for caveats.)
  [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 the 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 => false  : inherit
  current directory:
    :chdir => str

The cmdname, arg1, ... form does not use the shell. However, on different OSes, different things are provided as built-in commands. An example of this is +‘echo’+, which is a built-in on Windows, but is a normal program on Linux and Mac OS X. This means that Process.spawn 'echo', '%Path%' will display the contents of the %Path% environment variable on Windows, but Process.spawn 'echo', '$PATH' prints the literal $PATH.

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, a positive integer, or nil. true and zero cause the process to be a process leader of a new process group. A non-zero positive integer causes the process to join the provided process group. The default value, nil, causes the process to remain in the same process group.

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 Process.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, an integer, 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, [:out, :err]=>"/dev/null") # write mode
pid = spawn(command, 3=>"/dev/null") # read mode

For stdout and stderr (and combination of them), 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 false 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.

Process.times → aProcessTms
::

Returns a Tms structure (see Process::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]

Process.uid → integer

Process::UID.rid → integer

Process::Sys.getuid → integer
::

Returns the (real) user ID of this process.

Process.uid   #=> 501

Process.uid= user → numeric
::

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

Process.wait() → integer

Process.wait(pid=-1, flags=0) → integer

Process.waitpid(pid=-1, flags=0) → integer
::

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

Process.wait2(pid=-1, flags=0) → [pid, status]

Process.waitpid2(pid=-1, flags=0) → [pid, status]
::

Waits for a child process to exit (see Process::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

Process.waitall → [ [pid1,status1], ...]
::

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>]]

Process.wait() → integer

Process.wait(pid=-1, flags=0) → integer

Process.waitpid(pid=-1, flags=0) → integer
::

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

Process.wait2(pid=-1, flags=0) → [pid, status]

Process.waitpid2(pid=-1, flags=0) → [pid, status]
::

Waits for a child process to exit (see Process::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