# `uv_process_t` — Process handle

Process handles will spawn a new process and allow the user to control it and establish communication channels with it using streams.

## Data types

type uv_process_t

  Process handle type.

type uv_process_options_t

  Options for spawning the process (passed to `uv_spawn()`.

      typedef struct uv_process_options_s {
          uv_exit_cb exit_cb;
          const char* file;
          char** args;
          char** env;
          const char* cwd;
          unsigned int flags;
          int stdio_count;
          uv_stdio_container_t* stdio;
          uv_uid_t uid;
          uv_gid_t gid;
      } uv_process_options_t;

typedef void (*uv_exit_cb)(uv_process_t*, int64_t exit_status, int term_signal)

  Type definition for callback passed in `uv_process_options_t` which will indicate the exit status and the signal that caused the process to terminate, if any.

enum uv_process_flags

  Flags to be set on the flags field of `uv_process_options_t`.

      enum uv_process_flags {
          /*
          * Set the child process' user id.
          */
          UV_PROCESS_SETUID = (1 << 0),
          /*
          * Set the child process' group id.
          */
          UV_PROCESS_SETGID = (1 << 1),
          /*
          * Do not wrap any arguments in quotes, or perform any other escaping, when
          * converting the argument list into a command line string. This option is
          * only meaningful on Windows systems. On Unix it is silently ignored.
          */
          UV_PROCESS_WINDOWS_VERBATIM_ARGUMENTS = (1 << 2),
          /*
          * Spawn the child process in a detached state - this will make it a process
          * group leader, and will effectively enable the child to keep running after
          * the parent exits. Note that the child process will still keep the
          * parent's event loop alive unless the parent process calls uv_unref() on
          * the child's process handle.
          */
          UV_PROCESS_DETACHED = (1 << 3),
          /*
          * Hide the subprocess window that would normally be created. This option is
          * only meaningful on Windows systems. On Unix it is silently ignored.
          */
          UV_PROCESS_WINDOWS_HIDE = (1 << 4),
          /*
          * Hide the subprocess console window that would normally be created. This
          * option is only meaningful on Windows systems. On Unix it is silently
          * ignored.
          */
          UV_PROCESS_WINDOWS_HIDE_CONSOLE = (1 << 5),
          /*
          * Hide the subprocess GUI window that would normally be created. This
          * option is only meaningful on Windows systems. On Unix it is silently
          * ignored.
          */
          UV_PROCESS_WINDOWS_HIDE_GUI = (1 << 6),
          /*
           * On Windows, if the path to the program to execute, specified in
           * uv_process_options_t's file field, has a directory component,
           * search for the exact file name before trying variants with
           * extensions like '.exe' or '.cmd'.
           */
          UV_PROCESS_WINDOWS_FILE_PATH_EXACT_NAME = (1 << 7)
      };

type uv_stdio_container_t

  Container for each stdio handle or fd passed to a child process.

      typedef struct uv_stdio_container_s {
          uv_stdio_flags flags;
          union {
              uv_stream_t* stream;
              int fd;
          } data;
      } uv_stdio_container_t;

enum uv_stdio_flags

  Flags specifying how a stdio should be transmitted to the child process.

      typedef enum {
          /*
          * The following four options are mutually-exclusive, and define
          * the operation to perform for the corresponding file descriptor
          * in the child process:
          */

          /*
          * No file descriptor will be provided (or redirected to
          * `/dev/null` if it is fd 0, 1 or 2).
          */
          UV_IGNORE = 0x00,

          /*
          * Open a new pipe into `data.stream`, per the flags below. The
          * `data.stream` field must point to a uv_pipe_t object that has
          * been initialized with `uv_pipe_init(loop, data.stream, ipc);`,
          * but not yet opened or connected.
          /*
          UV_CREATE_PIPE = 0x01,

          /*
          * The child process will be given a duplicate of the parent's
          * file descriptor given by `data.fd`.
          */
          UV_INHERIT_FD = 0x02,

          /*
          * The child process will be given a duplicate of the parent's
          * file descriptor being used by the stream handle given by
          * `data.stream`.
          */
          UV_INHERIT_STREAM = 0x04,

          /*
          * When UV_CREATE_PIPE is specified, UV_READABLE_PIPE and UV_WRITABLE_PIPE
          * determine the direction of flow, from the child process' perspective. Both
          * flags may be specified to create a duplex data stream.
          */
          UV_READABLE_PIPE = 0x10,
          UV_WRITABLE_PIPE = 0x20,

          /*
          * When UV_CREATE_PIPE is specified, specifying UV_NONBLOCK_PIPE opens the
          * handle in non-blocking mode in the child. This may cause loss of data,
          * if the child is not designed to handle to encounter this mode,
          * but can also be significantly more efficient.
          */
          UV_NONBLOCK_PIPE = 0x40
      } uv_stdio_flags;

### Public members

int uv_process_t.pid

  The PID of the spawned process. It’s set after calling `uv_spawn()`.

Note

The `uv_handle_t` members also apply.

uv_exit_cb uv_process_options_t.exit_cb

  Callback called after the process exits.

const char *uv_process_options_t.file

  Path pointing to the program to be executed.

char **uv_process_options_t.args

  Command line arguments. args[0] should be the path to the program. On Windows this uses CreateProcess which concatenates the arguments into a string this can cause some strange errors. See the `UV_PROCESS_WINDOWS_VERBATIM_ARGUMENTS` flag on `uv_process_flags`.

char **uv_process_options_t.env

  Environment for the new process. If NULL the parents environment is used.

const char *uv_process_options_t.cwd

  Current working directory for the subprocess.

unsigned int uv_process_options_t.flags

  Various flags that control how `uv_spawn()` behaves. See `uv_process_flags`.

int uv_process_options_t.stdio_count

uv_stdio_container_t *uv_process_options_t.stdio

  The stdio field points to an array of `uv_stdio_container_t` structs that describe the file descriptors that will be made available to the child process. The convention is that stdio[0] points to stdin, fd 1 is used for stdout, and fd 2 is stderr.

  Note

  On Windows file descriptors greater than 2 are available to the child process only if the child processes uses the MSVCRT runtime.

uv_uid_t uv_process_options_t.uid

uv_gid_t uv_process_options_t.gid

  Libuv can change the child process’ user/group id. This happens only when the appropriate bits are set in the flags fields.

  Note

  This is not supported on Windows, `uv_spawn()` will fail and set the error to `UV_ENOTSUP`.

uv_stdio_flags uv_stdio_container_t.flags

  Flags specifying how the stdio container should be passed to the child.

union [anonymous] uv_stdio_container_t.data

  Union containing either the stream or fd to be passed on to the child process.

## API

void uv_disable_stdio_inheritance(void)

  Disables inheritance for file descriptors / handles that this process inherited from its parent. The effect is that child processes spawned by this process don’t accidentally inherit these handles.

  It is recommended to call this function as early in your program as possible, before the inherited file descriptors can be closed or duplicated.

  Note

  This function works on a best-effort basis: there is no guarantee that libuv can discover all file descriptors that were inherited. In general it does a better job on Windows than it does on Unix.

int uv_spawn(uv_loop_t *loop, uv_process_t *handle, const uv_process_options_t *options)

  Initializes the process handle and starts the process. If the process is successfully spawned, this function will return 0. Otherwise, the negative error code corresponding to the reason it couldn’t spawn is returned.

  Possible reasons for failing to spawn would include (but not be limited to) the file to execute not existing, not having permissions to use the setuid or setgid specified, or not having enough memory to allocate for the new process.

  Changed in version 1.24.0: Added UV_PROCESS_WINDOWS_HIDE_CONSOLE and UV_PROCESS_WINDOWS_HIDE_GUI flags.

  Changed in version 1.48.0: Added the UV_PROCESS_WINDOWS_FILE_PATH_EXACT_NAME flag.

int uv_process_kill(uv_process_t *handle, int signum)

  Sends the specified signal to the given process handle. Check the documentation on uv_signal_t — Signal handle for signal support, specially on Windows.

int uv_kill(int pid, int signum)

  Sends the specified signal to the given PID. Check the documentation on uv_signal_t — Signal handle for signal support, specially on Windows.

uv_pid_t uv_process_get_pid(const uv_process_t *handle)

  Returns handle->pid.

  Added in version 1.19.0.

See also

The `uv_handle_t` API functions also apply.