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<body class="article toc2 toc-left">
<div id="header">
<h1>cockpit.js: Spawning Processes</h1>
<div id="toc" class="toc2">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#cockpit-spawn-spawn">cockpit.spawn()</a></li>
<li><a href="#cockpit-spawn-script">cockpit.script()</a></li>
<li><a href="#cockpit-spawn-then">process.then()</a></li>
<li><a href="#cockpit-spawn-catch">process.catch()</a></li>
<li><a href="#cockpit-spawn-stream">process.stream()</a></li>
<li><a href="#cockpit-spawn-input">process.input()</a></li>
<li><a href="#cockpit-spawn-close">process.close()</a></li>
</ul>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>This is the API for spawning a process and receiving its output, as well
as exit codes.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-spawn">cockpit.spawn()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process = cockpit.spawn(args, [options])</pre>
</div>
</div>
<div class="paragraph">
<p>Spawns a process on the system.</p>
</div>
<div class="paragraph">
<p>The <code>args</code> should be an array starting with the executable and
containing all the arguments to pass on the command line. If <code>args</code> is
a string then it is interpreted as an executable name. The optional
<code>options</code> argument is a javascript plain object and can contain any of
the following fields:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>"binary"</code></dt>
<dd>
<p>If set to <code>true</code> then handle the input and output of the process as
arrays of binary bytes.</p>
</dd>
<dt class="hdlist1"><code>"directory"</code></dt>
<dd>
<p>The directory to spawn the process in.</p>
</dd>
<dt class="hdlist1"><code>"err"</code></dt>
<dd>
<p>Controls where the standard error is sent. By default it is logged to
the journal. If set to <code>"out"</code> it is included in with the output
data. If set to <code>"ignore"</code> then the error output is discarded. If
set to <code>"message"</code>, then it will be returned as the error message.
When the <code>"pty"</code> field is set, this field has no effect.</p>
</dd>
<dt class="hdlist1"><code>"environ"</code></dt>
<dd>
<p>An optional array that contains strings to be used as additional
environment variables for the new process. These are <code>"NAME=VALUE"</code>
strings.</p>
</dd>
<dt class="hdlist1"><code>"pty"</code></dt>
<dd>
<p>Launch the process in its own PTY terminal, and send/receive terminal
input and output.</p>
</dd>
<dt class="hdlist1"><code>"batch"</code></dt>
<dd>
<p>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.</p>
</dd>
<dt class="hdlist1"><code>"latency"</code></dt>
<dd>
<p>The timeout for flushing any cached data in milliseconds.</p>
</dd>
<dt class="hdlist1"><code>"superuser"</code></dt>
<dd>
<p>Set to <code>"require"</code> 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 <code>pkexec</code>) then the <code>client</code> will immediately
be <a href="#cockpit-dbus-onclose">closed</a> with a <code>"access-denied"</code>
problem code.
+
Set to <code>"try"</code> to try to run the process as root, but if that fails,
fall back to an unprivileged process.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>The spawned process is a
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise">promise</a>
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.</p>
</div>
<div class="paragraph">
<p>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.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-script">cockpit.script()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process = cockpit.script(script, [args], [options])</pre>
</div>
</div>
<div class="paragraph">
<p>Run a shell script on the system.</p>
</div>
<div class="paragraph">
<p>This function <a href="#cockpit-spawn-spawn">spawns</a> a Bourne shell script
process. The full text of the <code>/bin/sh</code> shell script should be passed
in as the first argument. The <code>args</code> can be an array of arguments, not
including the executable, which are passed to the script as <code>$1</code>,
<code>$2</code> and so on. Shebang options are not used or respected.</p>
</div>
<div class="paragraph">
<p>The <code>options</code> is an optional javascript plain object and can include
any of the fields listed for the
<a href="#cockpit-spawn-spawn"><code>cockpit.spawn()</code></a> function.</p>
</div>
<div class="paragraph">
<p>The spawned process is a
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise">promise</a>
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.</p>
</div>
<div class="paragraph">
<p>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.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-then">process.then()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process.then((data[, message]) => { ... })</pre>
</div>
</div>
<div class="paragraph">
<p>This is a standard
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise">promise</a>
method. It sets up a handler to be called when the process finishes
successfully.</p>
</div>
<div class="paragraph">
<p>The <code>data</code> argument contains the standard output of the process. If it
a string, unless the process was opened in binary mode, in which case
the <code>data</code> is an array of bytes. If a <code>process.stream()</code> handler is
set up, then any standard output data consumed by the handler will not
be included in the <code>data</code> argument.</p>
</div>
<div class="paragraph">
<p>If the process was spawned with the <code>"err"</code> option set to
<code>"message"</code> then the second argument will contain the standard error
output of the process.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-catch">process.catch()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process.catch((exception[, data]) => { ... })</pre>
</div>
</div>
<div class="paragraph">
<p>This is a standard
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise">Promise</a>
method. It sets up a handler to be called when the process fails,
terminates or exits.</p>
</div>
<div class="paragraph">
<p>The <code>exception</code> object passed to the handler can have the following
fields:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>message</code></dt>
<dd>
<p>A message describing the exception. If the process was spawned with
the <code>"err"</code> option set to <code>"message"</code> then the second argument
will contain the standard error output of the process.</p>
</dd>
<dt class="hdlist1"><code>problem</code></dt>
<dd>
<p>A <a href="#cockpit-problems">problem code</a> string when a problem occurred
starting or communicating with the process. This is <code>null</code> if the
process exited or was terminated.</p>
</dd>
<dt class="hdlist1"><code>exit_status</code></dt>
<dd>
<p>The numeric exit status of the process. This is <code>null</code> if the
process did not exit.</p>
</dd>
<dt class="hdlist1"><code>exit_signal</code></dt>
<dd>
<p>A string representing a unix signal that caused the process to
terminate. This is <code>null</code> if the process did not terminate because
of a signal.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>If the process actually ran and produced output before failing, it will
be available in the <code>data</code> argument. Otherwise this argument will be
<code>undefined</code>.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-stream">process.stream()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process.stream(data => { ... })</pre>
</div>
</div>
<div class="paragraph">
<p>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.</p>
</div>
<div class="paragraph">
<p>Only one handler may be registered at a time. Registering an additional
handler replaces the previous one. The handler receives either string
<code>data</code> 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 <code>data</code>. Any data not consumed will be included again the
next time the handler is called.</p>
</div>
<div class="paragraph">
<p>If a <code>process.stream()</code> handler is set up, then the <code>process.then()</code>
handlers will only get any remaining data not consumed by the stream
handler.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-input">process.input()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process.input(data, [stream])</pre>
</div>
</div>
<div class="paragraph">
<p>This method writes <code>data</code> to the standard input of the process. If
<code>data</code> is <code>null</code> or <code>undefined</code> it is not sent. The <code>data</code>
should be a string or an array of bytes if the process was opened in
binary mode.</p>
</div>
<div class="paragraph">
<p>If <code>stream</code> is set to <code>true</code> then this function may be called again
with further input. Otherwise the standard input of the process is
closed.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="cockpit-spawn-close">process.close()</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre>process.close([problem])</pre>
</div>
</div>
<div class="paragraph">
<p>Close the process by closing its standard input and output. If
<code>problem</code> is specified it should be a standard
<a href="#cockpit-problems">problem code</a> string. In this case the process
will be terminated with a signal.</p>
</div>
</div>
</div>
</div>
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<div id="footer-text">
Last updated 2026-01-28 11:12:25 UTC
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