Spawning Processes

## Spawning Processes Spawning Processes — process launching |

## Synopsis

    #include <glib.h>

    enum                GSpawnError;
    #define             G_SPAWN_ERROR
    enum                GSpawnFlags;
    void                (*GSpawnChildSetupFunc)             (gpointer user_data);
    gboolean            g_spawn_async_with_pipes            (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             GPid *child_pid,
                                                             gint *standard_input,
                                                             gint *standard_output,
                                                             gint *standard_error,
                                                             GError **error);
    gboolean            g_spawn_async                       (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             GPid *child_pid,
                                                             GError **error);
    gboolean            g_spawn_sync                        (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             gchar **standard_output,
                                                             gchar **standard_error,
                                                             gint *exit_status,
                                                             GError **error);
    gboolean            g_spawn_command_line_async          (const gchar *command_line,
                                                             GError **error);
    gboolean            g_spawn_command_line_sync           (const gchar *command_line,
                                                             gchar **standard_output,
                                                             gchar **standard_error,
                                                             gint *exit_status,
                                                             GError **error);
    void                g_spawn_close_pid                   (GPid pid);

## Description

## Details

### enum GSpawnError

    typedef enum {
      G_SPAWN_ERROR_FORK,   /* fork failed due to lack of memory */
      G_SPAWN_ERROR_READ,   /* read or select on pipes failed */
      G_SPAWN_ERROR_CHDIR,  /* changing to working dir failed */
      G_SPAWN_ERROR_ACCES,  /* execv() returned EACCES */
      G_SPAWN_ERROR_PERM,   /* execv() returned EPERM */
      G_SPAWN_ERROR_2BIG,   /* execv() returned E2BIG */
      G_SPAWN_ERROR_NOEXEC, /* execv() returned ENOEXEC */
      G_SPAWN_ERROR_NAMETOOLONG, /* ""  "" ENAMETOOLONG */
      G_SPAWN_ERROR_NOENT,       /* ""  "" ENOENT */
      G_SPAWN_ERROR_NOMEM,       /* ""  "" ENOMEM */
      G_SPAWN_ERROR_NOTDIR,      /* ""  "" ENOTDIR */
      G_SPAWN_ERROR_LOOP,        /* ""  "" ELOOP   */
      G_SPAWN_ERROR_TXTBUSY,     /* ""  "" ETXTBUSY */
      G_SPAWN_ERROR_IO,          /* ""  "" EIO */
      G_SPAWN_ERROR_NFILE,       /* ""  "" ENFILE */
      G_SPAWN_ERROR_MFILE,       /* ""  "" EMFLE */
      G_SPAWN_ERROR_INVAL,       /* ""  "" EINVAL */
      G_SPAWN_ERROR_ISDIR,       /* ""  "" EISDIR */
      G_SPAWN_ERROR_LIBBAD,      /* ""  "" ELIBBAD */
      G_SPAWN_ERROR_FAILED       /* other fatal failure, error->message
                                  * should explain
                                  */
    } GSpawnError;

Error codes returned by spawning processes.

`G_SPAWN_ERROR_FORK` | Fork failed due to lack of memory.
`G_SPAWN_ERROR_READ` | Read or select on pipes failed.
`G_SPAWN_ERROR_CHDIR` | Changing to working directory failed.
`G_SPAWN_ERROR_ACCES` | execv() returned `EACCES`.
`G_SPAWN_ERROR_PERM` | execv() returned `EPERM`.
`G_SPAWN_ERROR_2BIG` | execv() returned `E2BIG`.
`G_SPAWN_ERROR_NOEXEC` | execv() returned `ENOEXEC`.
`G_SPAWN_ERROR_NAMETOOLONG` | execv() returned `ENAMETOOLONG`.
`G_SPAWN_ERROR_NOENT` | execv() returned `ENOENT`.
`G_SPAWN_ERROR_NOMEM` | execv() returned `ENOMEM`.
`G_SPAWN_ERROR_NOTDIR` | execv() returned `ENOTDIR`.
`G_SPAWN_ERROR_LOOP` | execv() returned `ELOOP`.
`G_SPAWN_ERROR_TXTBUSY` | execv() returned `ETXTBUSY`.
`G_SPAWN_ERROR_IO` | execv() returned `EIO`.
`G_SPAWN_ERROR_NFILE` | execv() returned `ENFILE`.
`G_SPAWN_ERROR_MFILE` | execv() returned `EMFILE`.
`G_SPAWN_ERROR_INVAL` | execv() returned `EINVAL`.
`G_SPAWN_ERROR_ISDIR` | execv() returned `EISDIR`.
`G_SPAWN_ERROR_LIBBAD` | execv() returned `ELIBBAD`.
`G_SPAWN_ERROR_FAILED` | Some other fatal failure, `error->message` should explain.

### G_SPAWN_ERROR

    #define G_SPAWN_ERROR g_spawn_error_quark ()

Error domain for spawning processes. Errors in this domain will be from the GSpawnError enumeration. See GError for information on error domains.

### enum GSpawnFlags

    typedef enum {
      G_SPAWN_LEAVE_DESCRIPTORS_OPEN = 1 << 0,
      G_SPAWN_DO_NOT_REAP_CHILD      = 1 << 1,
      /* look for argv[0] in the path i.e. use execvp() */
      G_SPAWN_SEARCH_PATH            = 1 << 2,
      /* Dump output to /dev/null */
      G_SPAWN_STDOUT_TO_DEV_NULL     = 1 << 3,
      G_SPAWN_STDERR_TO_DEV_NULL     = 1 << 4,
      G_SPAWN_CHILD_INHERITS_STDIN   = 1 << 5,
      G_SPAWN_FILE_AND_ARGV_ZERO     = 1 << 6
    } GSpawnFlags;

Flags passed to `g_spawn_sync()`, `g_spawn_async()` and `g_spawn_async_with_pipes()`.

`G_SPAWN_LEAVE_DESCRIPTORS_OPEN` | the parent's open file descriptors will be inherited by the child; otherwise all descriptors except stdin/stdout/stderr will be closed before calling `exec()` in the child.
`G_SPAWN_DO_NOT_REAP_CHILD` | the child will not be automatically reaped; you must use `g_child_watch_add()` yourself (or call `waitpid()` or handle `SIGCHLD` yourself), or the child will become a zombie.
`G_SPAWN_SEARCH_PATH` | `argv[0]` need not be an absolute path, it will be looked for in the user's `PATH`.
`G_SPAWN_STDOUT_TO_DEV_NULL` | the child's standard output will be discarded, instead of going to the same location as the parent's standard output.
`G_SPAWN_STDERR_TO_DEV_NULL` | the child's standard error will be discarded.
`G_SPAWN_CHILD_INHERITS_STDIN` | the child will inherit the parent's standard input (by default, the child's standard input is attached to `/dev/null`).
`G_SPAWN_FILE_AND_ARGV_ZERO` | the first element of `argv` is the file to execute, while the remaining elements are the actual argument vector to pass to the file. Normally `g_spawn_async_with_pipes()` uses `argv[0]` as the file to execute, and passes all of `argv` to the child.

### GSpawnChildSetupFunc ()

    void                (*GSpawnChildSetupFunc)             (gpointer user_data);

Specifies the type of the setup function passed to `g_spawn_async()`, `g_spawn_sync()` and `g_spawn_async_with_pipes()`. On POSIX platforms it is called in the child after GLib has performed all the setup it plans to perform but before calling `exec()`. On POSIX actions taken in this function will thus only affect the child, not the parent.

Note that POSIX allows only async-signal-safe functions (see signal(7)) to be called in the child between `fork()` and `exec()`, which drastically limits the usefulness of child setup functions.

Also note that modifying the environment from the child setup function may not have the intended effect, since it will get overridden by a non-`NULL` `env` argument to the `g_spawn...` functions.

On Windows the function is called in the parent. Its usefulness on Windows is thus questionable. In many cases executing the child setup function in the parent can have ill effects, and you should be very careful when porting software to Windows that uses child setup functions.

`user_data` : | user data to pass to the function.

### g_spawn_async_with_pipes ()

    gboolean            g_spawn_async_with_pipes            (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             GPid *child_pid,
                                                             gint *standard_input,
                                                             gint *standard_output,
                                                             gint *standard_error,
                                                             GError **error);

Executes a child program asynchronously (your program will not block waiting for the child to exit). The child program is specified by the only argument that must be provided, `argv`. `argv` should be a `NULL`-terminated array of strings, to be passed as the argument vector for the child. The first string in `argv` is of course the name of the program to execute. By default, the name of the program must be a full path; the `PATH` shell variable will only be searched if you pass the `G_SPAWN_SEARCH_PATH` flag. If the program name is not a full path and `G_SPAWN_SEARCH_PATH` flag is not used, then the program will be run from the current directory (or `working_directory`, if specified); this might be unexpected or even dangerous in some cases when the current directory is world-writable.

On Windows, note that all the string or string vector arguments to this function and the other g_spawn*() functions are in UTF-8, the GLib file name encoding. Unicode characters that are not part of the system codepage passed in these arguments will be correctly available in the spawned program only if it uses wide character API to retrieve its command line. For C programs built with Microsoft's tools it is enough to make the program have a `wmain()` instead of `main()`. `wmain()` has a wide character argument vector as parameter.

At least currently, mingw doesn't support `wmain()`, so if you use mingw to develop the spawned program, it will have to call the undocumented function `__wgetmainargs()` to get the wide character argument vector and environment. See gspawn-win32-helper.c in the GLib sources or init.c in the mingw runtime sources for a prototype for that function. Alternatively, you can retrieve the Win32 system level wide character command line passed to the spawned program using the `GetCommandLineW()` function.

On Windows the low-level child process creation API ``CreateProcess()`` doesn't use argument vectors, but a command line. The C runtime library's `spawn*()` family of functions (which `g_spawn_async_with_pipes()` eventually calls) paste the argument vector elements together into a command line, and the C runtime startup code does a corresponding reconstruction of an argument vector from the command line, to be passed to `main()`. Complications arise when you have argument vector elements that contain spaces of double quotes. The `spawn*()` functions don't do any quoting or escaping, but on the other hand the startup code does do unquoting and unescaping in order to enable receiving arguments with embedded spaces or double quotes. To work around this asymmetry, `g_spawn_async_with_pipes()` will do quoting and escaping on argument vector elements that need it before calling the C runtime `spawn()` function.

The returned `child_pid` on Windows is a handle to the child process, not its identifier. Process handles and process identifiers are different concepts on Windows.

`envp` is a `NULL`-terminated array of strings, where each string has the form `KEY=VALUE`. This will become the child's environment. If `envp` is `NULL`, the child inherits its parent's environment.

`flags` should be the bitwise OR of any flags you want to affect the function's behaviour. The `G_SPAWN_DO_NOT_REAP_CHILD` means that the child will not automatically be reaped; you must use a child watch to be notified about the death of the child process. Eventually you must call `g_spawn_close_pid()` on the `child_pid`, in order to free resources which may be associated with the child process. (On Unix, using a child watch is equivalent to calling `waitpid()` or handling the `SIGCHLD` signal manually. On Windows, calling `g_spawn_close_pid()` is equivalent to calling `CloseHandle()` on the process handle returned in `child_pid`). See `g_child_watch_add()`.

`G_SPAWN_LEAVE_DESCRIPTORS_OPEN` means that the parent's open file descriptors will be inherited by the child; otherwise all descriptors except stdin/stdout/stderr will be closed before calling `exec()` in the child. `G_SPAWN_SEARCH_PATH` means that `argv[0]` need not be an absolute path, it will be looked for in the user's `PATH`. `G_SPAWN_STDOUT_TO_DEV_NULL` means that the child's standard output will be discarded, instead of going to the same location as the parent's standard output. If you use this flag, `standard_output` must be `NULL`. `G_SPAWN_STDERR_TO_DEV_NULL` means that the child's standard error will be discarded, instead of going to the same location as the parent's standard error. If you use this flag, `standard_error` must be `NULL`. `G_SPAWN_CHILD_INHERITS_STDIN` means that the child will inherit the parent's standard input (by default, the child's standard input is attached to /dev/null). If you use this flag, `standard_input` must be `NULL`. `G_SPAWN_FILE_AND_ARGV_ZERO` means that the first element of `argv` is the file to execute, while the remaining elements are the actual argument vector to pass to the file. Normally `g_spawn_async_with_pipes()` uses `argv`[0] as the file to execute, and passes all of `argv` to the child.

`child_setup` and `user_data` are a function and user data. On POSIX platforms, the function is called in the child after GLib has performed all the setup it plans to perform (including creating pipes, closing file descriptors, etc.) but before calling `exec()`. That is, `child_setup` is called just before calling `exec()` in the child. Obviously actions taken in this function will only affect the child, not the parent.

On Windows, there is no separate `fork()` and `exec()` functionality. Child processes are created and run with a single API call, `CreateProcess()`. There is no sensible thing `child_setup` could be used for on Windows so it is ignored and not called.

If non-`NULL`, `child_pid` will on Unix be filled with the child's process ID. You can use the process ID to send signals to the child, or to use `g_child_watch_add()` (or `waitpid()`) if you specified the `G_SPAWN_DO_NOT_REAP_CHILD` flag. On Windows, `child_pid` will be filled with a handle to the child process only if you specified the `G_SPAWN_DO_NOT_REAP_CHILD` flag. You can then access the child process using the Win32 API, for example wait for its termination with the `WaitFor*()` functions, or examine its exit code with `GetExitCodeProcess()`. You should close the handle with `CloseHandle()` or `g_spawn_close_pid()` when you no longer need it.

If non-`NULL`, the `standard_input`, `standard_output`, `standard_error` locations will be filled with file descriptors for writing to the child's standard input or reading from its standard output or standard error. The caller of `g_spawn_async_with_pipes()` must close these file descriptors when they are no longer in use. If these parameters are `NULL`, the corresponding pipe won't be created.

If `standard_input` is NULL, the child's standard input is attached to /dev/null unless `G_SPAWN_CHILD_INHERITS_STDIN` is set.

If `standard_error` is NULL, the child's standard error goes to the same location as the parent's standard error unless `G_SPAWN_STDERR_TO_DEV_NULL` is set.

If `standard_output` is NULL, the child's standard output goes to the same location as the parent's standard output unless `G_SPAWN_STDOUT_TO_DEV_NULL` is set.

`error` can be `NULL` to ignore errors, or non-`NULL` to report errors. If an error is set, the function returns `FALSE`. Errors are reported even if they occur in the child (for example if the executable in `argv[0]` is not found). Typically the `message` field of returned errors should be displayed to users. Possible errors are those from the G_SPAWN_ERROR domain.

If an error occurs, `child_pid`, `standard_input`, `standard_output`, and `standard_error` will not be filled with valid values.

If `child_pid` is not `NULL` and an error does not occur then the returned process reference must be closed using `g_spawn_close_pid()`.

### Note

If you are writing a GTK+ application, and the program you are spawning is a graphical application, too, then you may want to use `gdk_spawn_on_screen_with_pipes()` instead to ensure that the spawned program opens its windows on the right screen.

`working_directory` : | child's current working directory, or `NULL` to inherit parent's, in the GLib file name encoding. [allow-none]
`argv` : | child's argument vector, in the GLib file name encoding. [array zero-terminated=1]
`envp` : | child's environment, or `NULL` to inherit parent's, in the GLib file name encoding. [array zero-terminated=1][allow-none]
`flags` : | flags from GSpawnFlags
`child_setup` : | function to run in the child just before `exec()`. [scope async][allow-none]
`user_data` : | user data for `child_setup`. [closure]
`child_pid` : | return location for child process ID, or `NULL`. [out][allow-none]
`standard_input` : | return location for file descriptor to write to child's stdin, or `NULL`. [out][allow-none]
`standard_output` : | return location for file descriptor to read child's stdout, or `NULL`. [out][allow-none]
`standard_error` : | return location for file descriptor to read child's stderr, or `NULL`. [out][allow-none]
`error` : | return location for error
Returns : | `TRUE` on success, `FALSE` if an error was set

### g_spawn_async ()

    gboolean            g_spawn_async                       (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             GPid *child_pid,
                                                             GError **error);

See `g_spawn_async_with_pipes()` for a full description; this function simply calls the `g_spawn_async_with_pipes()` without any pipes.

You should call `g_spawn_close_pid()` on the returned child process reference when you don't need it any more.

### Note

If you are writing a GTK+ application, and the program you are spawning is a graphical application, too, then you may want to use `gdk_spawn_on_screen()` instead to ensure that the spawned program opens its windows on the right screen.

### Note

Note that the returned `child_pid` on Windows is a handle to the child process and not its identifier. Process handles and process identifiers are different concepts on Windows.

`working_directory` : | child's current working directory, or `NULL` to inherit parent's. [allow-none]
`argv` : | child's argument vector. [array zero-terminated=1]
`envp` : | child's environment, or `NULL` to inherit parent's. [array zero-terminated=1][allow-none]
`flags` : | flags from GSpawnFlags
`child_setup` : | function to run in the child just before `exec()`. [scope async][allow-none]
`user_data` : | user data for `child_setup`. [closure]
`child_pid` : | return location for child process reference, or `NULL`. [out][allow-none]
`error` : | return location for error
Returns : | `TRUE` on success, `FALSE` if error is set

### g_spawn_sync ()

    gboolean            g_spawn_sync                        (const gchar *working_directory,
                                                             gchar **argv,
                                                             gchar **envp,
                                                             GSpawnFlags flags,
                                                             GSpawnChildSetupFunc child_setup,
                                                             gpointer user_data,
                                                             gchar **standard_output,
                                                             gchar **standard_error,
                                                             gint *exit_status,
                                                             GError **error);

Executes a child synchronously (waits for the child to exit before returning). All output from the child is stored in `standard_output` and `standard_error`, if those parameters are non-`NULL`. Note that you must set the `G_SPAWN_STDOUT_TO_DEV_NULL` and `G_SPAWN_STDERR_TO_DEV_NULL` flags when passing `NULL` for `standard_output` and `standard_error`. If `exit_status` is non-`NULL`, the exit status of the child is stored there as it would be returned by `waitpid()`; standard UNIX macros such as `WIFEXITED()` and `WEXITSTATUS()` must be used to evaluate the exit status. Note that this function call `waitpid()` even if `exit_status` is `NULL`, and does not accept the `G_SPAWN_DO_NOT_REAP_CHILD` flag. If an error occurs, no data is returned in `standard_output`, `standard_error`, or `exit_status`.

This function calls `g_spawn_async_with_pipes()` internally; see that function for full details on the other parameters and details on how these functions work on Windows.

`working_directory` : | child's current working directory, or `NULL` to inherit parent's. [allow-none]
`argv` : | child's argument vector. [array zero-terminated=1]
`envp` : | child's environment, or `NULL` to inherit parent's. [array zero-terminated=1][allow-none]
`flags` : | flags from GSpawnFlags
`child_setup` : | function to run in the child just before `exec()`. [scope async][allow-none]
`user_data` : | user data for `child_setup`. [closure]
`standard_output` : | return location for child output, or `NULL`. [out][array zero-terminated=1][element-type guint8][allow-none]
`standard_error` : | return location for child error messages, or `NULL`. [out][array zero-terminated=1][element-type guint8][allow-none]
`exit_status` : | return location for child exit status, as returned by `waitpid()`, or `NULL`. [out][allow-none]
`error` : | return location for error, or `NULL`
Returns : | `TRUE` on success, `FALSE` if an error was set.

### g_spawn_command_line_async ()

    gboolean            g_spawn_command_line_async          (const gchar *command_line,
                                                             GError **error);

A simple version of `g_spawn_async()` that parses a command line with `g_shell_parse_argv()` and passes it to `g_spawn_async()`. Runs a command line in the background. Unlike `g_spawn_async()`, the `G_SPAWN_SEARCH_PATH` flag is enabled, other flags are not. Note that `G_SPAWN_SEARCH_PATH` can have security implications, so consider using `g_spawn_async()` directly if appropriate. Possible errors are those from `g_shell_parse_argv()` and `g_spawn_async()`.

The same concerns on Windows apply as for `g_spawn_command_line_sync()`.

`command_line` : | a command line
`error` : | return location for errors
Returns : | `TRUE` on success, `FALSE` if error is set.

### g_spawn_command_line_sync ()

    gboolean            g_spawn_command_line_sync           (const gchar *command_line,
                                                             gchar **standard_output,
                                                             gchar **standard_error,
                                                             gint *exit_status,
                                                             GError **error);

A simple version of `g_spawn_sync()` with little-used parameters removed, taking a command line instead of an argument vector. See `g_spawn_sync()` for full details. `command_line` will be parsed by `g_shell_parse_argv()`. Unlike `g_spawn_sync()`, the `G_SPAWN_SEARCH_PATH` flag is enabled. Note that `G_SPAWN_SEARCH_PATH` can have security implications, so consider using `g_spawn_sync()` directly if appropriate. Possible errors are those from `g_spawn_sync()` and those from `g_shell_parse_argv()`.

If `exit_status` is non-`NULL`, the exit status of the child is stored there as it would be returned by `waitpid()`; standard UNIX macros such as `WIFEXITED()` and `WEXITSTATUS()` must be used to evaluate the exit status.

On Windows, please note the implications of `g_shell_parse_argv()` parsing `command_line`. Parsing is done according to Unix shell rules, not Windows command interpreter rules. Space is a separator, and backslashes are special. Thus you cannot simply pass a `command_line` containing canonical Windows paths, like "c:\\program files\\app\\app.exe", as the backslashes will be eaten, and the space will act as a separator. You need to enclose such paths with single quotes, like "'c:\\program files\\app\\app.exe' 'e:\\folder\\argument.txt'".

`command_line` : | a command line
`standard_output` : | return location for child output. [out][array zero-terminated=1][element-type guint8][allow-none]
`standard_error` : | return location for child errors. [out][array zero-terminated=1][element-type guint8][allow-none]
`exit_status` : | return location for child exit status, as returned by `waitpid()`. [out][allow-none]
`error` : | return location for errors
Returns : | `TRUE` on success, `FALSE` if an error was set

### g_spawn_close_pid ()

    void                g_spawn_close_pid                   (GPid pid);

On some platforms, notably Windows, the GPid type represents a resource which must be closed to prevent resource leaking. `g_spawn_close_pid()` is provided for this purpose. It should be used on all platforms, even though it doesn't do anything under UNIX.

`pid` : | The process reference to close