BSD-3-Clause licensed
Maintained by [email protected]
This version can be pinned in stack with:process-,3025

Module documentation for

This package contains libraries for dealing with system processes.

The typed-process package is a more recent take on a process API, which uses this package internally. It features better binary support, easier concurrency, and a more composable API. You can read more about it at


Changelog for process package September 2023

  • Fix deadlock when waiting for process completion and process jobs #273
  • Support delegate_ctlc on Windows. #278
  • Drop support for vfork #261
  • Javascript backend support
  • Fix potential segmentation fault on macOS #295 February 2023

  • Improved documentation for the OpenExtHandle constructor. October 2022

  • posix_spawn: Don’t rely on addclose not failing for closed fds #251
  • Support unix 2.8 #258 August 2022

  • Correct permissions on createPipe on Windows 234
  • Ensure that both ends of pipes on Windows are created in the same mode 234
  • Fixed an issue with WINIO where giving an application an inherited pipe can cause it to misbehave 245
  • Set the encoding on WINIO created pipes to the local encoding as with MIO 248
  • cbits/fork-exec: Don’t dup2 identical fds #250 February 2022

  • posix: Ensure that errno is set after posix_spawnp fails #228
  • Fix waitForProcess not closing process handles with delegate_ctlc #231
  • Don’t use posix_spawn on platforms where it does not report ENOENT in caes where the requested executable does not exist #224
  • Ensure that find_executable correctly-locates executables when a change in working directory is requested #219
  • Fix capitalization error allowing execvpe to be used when available. July 2021

  • posix_spawn: Don’t attempt to dup2 identical fds #214 July 2021

  • Patches for the previous release July 2021

  • Refactoring of POSIX process logic #208 June 2021

  • Add function getCurrentPid to get the currently executing process’ ID #205 January 2021

  • Windows: Add support for new I/O manager in GHC 8.12#177
  • Deprecate use of createPipeFd in favor of createPipe
  • Fix MVar re-entrant problem on Windows with terminateProcess and process jobs. See #199 June 2020

  • Give a usable buffer to _pipe on Windows #182

1.6.9 May 2020

  • Windows: Fix buffer size of QueryInformationJobObject request #176 March 2020

  • Fix another process wait bug on Windows. March 2020

  • Fix a few warnings on Windows. February 2020

  • Fix several bugs on Windows where use of process jobs would result in the process being prematurely terminated. See #168. November 2019

  • Fix a race condition on Windows that happens when you use process jobs and one of the child processes terminates but doesn’t release its resources immediately. Control returns to the caller too soon in this scenario. See #159 October 2019

  • Fix a potential privilege escalation issue (or, more precisely, privileges not being dropped when this was the user’s intent) where the groups of the spawning process’s user would be incorrectly retained due to a missing call to initgroups [#149].
  • Bug fix: Prevent stripping undecodable bytes from environment variables when in a non-unicode locale. #152
  • Expose runInteractiveProcess_lock in System.Process.Internals #154 June 2019

  • Version bound bumps
  • Slightly nicer error messages for internal errors December 2018

  • Bug fix: On Windows ignore ERROR_ACCESS_DENIED for TerminateProcess() if the process did terminate #110
  • Improve documentation of the NoStream data constructor July 2018

  • Bug fix: Don’t leak pipes on failure #122
  • Expose cleanupProcess from System.Process #130
  • Drop support for GHC before 7.10.3 January 2018

  • Added getPid and export of platform specific Pid type #109 October 2017

  • Allow async exceptions to be delivered to masked thread calling waitForProcess #101
  • Update Win32 package version to 2.6.x July 2017

  • Expose CGid, GroupID, and UserID from System.Process.Internals #90 #91 February 2017

  • Fix: waitForProcess race condition #46 #58 February 2017

  • Bug fix: Don’t close already closed pipes #81
  • Relax version bounds of Win32 to allow 2.5.
  • Add support for monitoring process tree for termination with the parameter use_process_jobs in CreateProcess on Windows. Also added a function terminateJob to kill entire process tree. December 2016

  • New exposed withCreateProcess
  • Derive Show and Eq for CreateProcess, CmdSpec, and StdStream January 2016

  • Added createPipeFD #52
    • New function createPipeFD added which returns a POSIX File Descriptor (CInt) instead of a GHC Handle to a pipe November 2015

  • Use less CPP #47
    • Refactor to have separate Windows and POSIX modules internally
    • Remove the broken non-GHC code paths November 2015

  • Added child_user and child_group to CreateProcess for unix. #45 August 2015

  • Add StdStream(NoStream) to have standard handles closed. #13
  • Support for Windows DETACHED_PROCESS and setsid #32
  • Support for Windows CREATE_NEW_CONSOLE #38 March 2015 Jan 2015

  • Fix delegated CTRL-C handling in createProcess in case of failed process creation. See issue #15 for more details.

  • waitpid on child PID after pre-exec failure in child to prevent zombies. See also issue #14. Dec 2014

  • Add support for base-

  • Remove Hugs98 specific code

  • New IsString CmdSpec instance

  • Expose documentation for System.Process.Internals

  • With GHC 7.10, System.Cmd and System.Process are now Safe (when compiled with older GHC versions they are just Trustworthy)

  • Expose createProcess_ function, and document behavior of UseHandle for createProcess. See issue #2.

  • New System.Process.createPipe operation. See also GHC #8943 Dec 2013

  • Update to Cabal 1.10 format
  • Remove NHC specific code
  • Add support for base-
  • Improve showCommandForUser to reduce redundant quoting
  • New functions callProcess, callCommand, spawnProcess and spawnCommand
  • Implement WCE handling according to
  • New delegate_ctlc field in CreateProcess for WCE handling
  • Use ExitFailure (-signum) on Unix when a proc is terminated due to a signal.
  • Deprecate module System.Cmd
  • On non-Windows, the child thread now comunicates any errors back to the parent thread via pipes.
  • Fix deadlocks in readProcess and readProcessWithExitCode