# cockpit.js: Spawning Processes

This is the API for spawning a process and receiving its output, as well as exit codes.

## cockpit.spawn()

    process = cockpit.spawn(args, [options])

Spawns a process on the system.

The `args` should be an array starting with the executable and containing all the arguments to pass on the command line. If `args` is a string then it is interpreted as an executable name. The optional `options` argument is a javascript plain object and can contain any of the following fields:

`"binary"`

  If set to `true` then handle the input and output of the process as arrays of binary bytes.

`"directory"`

  The directory to spawn the process in.

`"err"`

  Controls where the standard error is sent. By default it is logged to the journal. If set to `"out"` it is included in with the output data. If set to `"ignore"` then the error output is discarded. If set to `"message"`, then it will be returned as the error message. When the `"pty"` field is set, this field has no effect.

`"environ"`

  An optional array that contains strings to be used as additional environment variables for the new process. These are `"NAME=VALUE"` strings.

`"pty"`

  Launch the process in its own PTY terminal, and send/receive terminal input and output.

`"batch"`

  Batch data coming from the process in blocks of at least this size. This is not a guarantee. After a short timeout the data will be sent even if the data doesn’t match the batch size. Defaults to zero.

`"latency"`

  The timeout for flushing any cached data in milliseconds.

`"superuser"`

  Set to `"require"` to spawn the process as root instead of the logged in user. If the currently logged in user is not permitted to become root (eg: via `pkexec`) then the `client` will immediately be closed with a `"access-denied"` problem code. + Set to `"try"` to try to run the process as root, but if that fails, fall back to an unprivileged process.

The spawned process is a promise that will complete if the process exits successfully, or fail if there’s a problem. Some additional methods besides the standard promise methods are documented below.

The standard output of the process is made available via the spawned process object. Any non-UTF8 output from the process will be coerced into textual form. It is highly recommended that only textual output be produced by the command. The standard error is logged to the journal.

## cockpit.script()

    process = cockpit.script(script, [args], [options])

Run a shell script on the system.

This function spawns a Bourne shell script process. The full text of the `/bin/sh` shell script should be passed in as the first argument. The `args` can be an array of arguments, not including the executable, which are passed to the script as `$1`, `$2` and so on. Shebang options are not used or respected.

The `options` is an optional javascript plain object and can include any of the fields listed for the `cockpit.spawn()` function.

The spawned process is a promise that will complete if the script exits successfully, or fail if there’s a problem. Some additional methods besides the standard promise methods are documented below.

The standard output of the process is made available via the spawned process object. Any non-UTF8 output from the process will be coerced into textual form. It is highly recommended that only textual output be produced by the command. The standard error is logged to the journal by default.

## process.then()

    process.then((data[, message]) => { ... })

This is a standard promise method. It sets up a handler to be called when the process finishes successfully.

The `data` argument contains the standard output of the process. If it a string, unless the process was opened in binary mode, in which case the `data` is an array of bytes. If a `process.stream()` handler is set up, then any standard output data consumed by the handler will not be included in the `data` argument.

If the process was spawned with the `"err"` option set to `"message"` then the second argument will contain the standard error output of the process.

## process.catch()

    process.catch((exception[, data]) => { ... })

This is a standard Promise method. It sets up a handler to be called when the process fails, terminates or exits.

The `exception` object passed to the handler can have the following fields:

`message`

  A message describing the exception. If the process was spawned with the `"err"` option set to `"message"` then the second argument will contain the standard error output of the process.

`problem`

  A problem code string when a problem occurred starting or communicating with the process. This is `null` if the process exited or was terminated.

`exit_status`

  The numeric exit status of the process. This is `null` if the process did not exit.

`exit_signal`

  A string representing a unix signal that caused the process to terminate. This is `null` if the process did not terminate because of a signal.

If the process actually ran and produced output before failing, it will be available in the `data` argument. Otherwise this argument will be `undefined`.

## process.stream()

    process.stream(data => { ... })

This sets up a handler to be called when the process has standard output. The handler will be called multiple times. The handler will be called regardless of whether the process ends up exiting successfully or not.

Only one handler may be registered at a time. Registering an additional handler replaces the previous one. The handler receives either string `data` or an array of binary bytes as its argument. A stream handler may return a number, which indicates the number of characters or bytes consumed from `data`. Any data not consumed will be included again the next time the handler is called.

If a `process.stream()` handler is set up, then the `process.then()` handlers will only get any remaining data not consumed by the stream handler.

## process.input()

    process.input(data, [stream])

This method writes `data` to the standard input of the process. If `data` is `null` or `undefined` it is not sent. The `data` should be a string or an array of bytes if the process was opened in binary mode.

If `stream` is set to `true` then this function may be called again with further input. Otherwise the standard input of the process is closed.

## process.close()

    process.close([problem])

Close the process by closing its standard input and output. If `problem` is specified it should be a standard problem code string. In this case the process will be terminated with a signal.