systemd-stable/man/systemd-ask-password.xml

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<refentry id="systemd-ask-password"
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-ask-password</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-ask-password</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-ask-password</refname>
    <refpurpose>Query the user for a system password</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-ask-password <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">MESSAGE</arg></command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-ask-password</command> may be used to query
    a system password or passphrase from the user, using a question
    message specified on the command line. When run from a TTY it will
    query a password on the TTY and print it to standard output. When
    run with no TTY or with <option>--no-tty</option> it will use the
    system-wide query mechanism, which allows active users to respond via
    several agents, listed below.</para>

    <para>The purpose of this tool is to query system-wide passwords
    — that is passwords not attached to a specific user account.
    Examples include: unlocking encrypted hard disks when they are
    plugged in or at boot, entering an SSL certificate passphrase for
    web and VPN servers.</para>

    <para>Existing agents are:
    <itemizedlist>

      <listitem><para>A boot-time password agent asking the user for
      passwords using
      <citerefentry project='die-net'><refentrytitle>plymouth</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      </para></listitem>

      <listitem><para>A boot-time password agent querying the user
      directly on the console —
      <citerefentry><refentrytitle>systemd-ask-password-console.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      </para></listitem>

      <listitem><para>An agent requesting password input via a
      <citerefentry project='man-pages'><refentrytitle>wall</refentrytitle><manvolnum>1</manvolnum></citerefentry>
      message —
      <citerefentry><refentrytitle>systemd-ask-password-wall.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      </para></listitem>

      <listitem><para>A TTY agent that is temporarily spawned during
      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
      invocations,</para></listitem>

      <listitem><para>A command line agent which can be started
      temporarily to process queued password
      requests — <command>systemd-tty-ask-password-agent --query</command>.
      </para></listitem>
    </itemizedlist></para>

    <para>Answering system-wide password queries is a privileged operation, hence
    all the agents listed above (except for the last one), run as privileged
    system services. The last one also needs elevated privileges, so
    should be run through
    <citerefentry project='die-net'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    or similar.</para>

    <para>Additional password agents may be implemented according to
    the <ulink
    url="https://www.freedesktop.org/wiki/Software/systemd/PasswordAgents">systemd
    Password Agent Specification</ulink>.</para>

    <para>If a password is queried on a TTY, the user may press TAB to
    hide the asterisks normally shown for each character typed.
    Pressing Backspace as first key achieves the same effect.</para>

  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The following options are understood:</para>

    <variablelist>
      <varlistentry>
        <term><option>--icon=</option></term>

        <listitem><para>Specify an icon name alongside the password
        query, which may be used in all agents supporting graphical
        display. The icon name should follow the <ulink
        url="http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html">XDG
        Icon Naming Specification</ulink>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--id=</option></term>
        <listitem><para>Specify an identifier for this password
        query. This identifier is freely choosable and allows
        recognition of queries by involved agents. It should include
        the subsystem doing the query and the specific object the
        query is done for. Example:
        <literal>--id=cryptsetup:/dev/sda5</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--keyname=</option></term>
        <listitem><para>Configure a kernel keyring key name to use as
        cache for the password. If set, then the tool will try to push
        any collected passwords into the kernel keyring of the root
        user, as a key of the specified name. If combined with
        <option>--accept-cached</option>, it will also try to retrieve
        such cached passwords from the key in the kernel keyring
        instead of querying the user right away. By using this option,
        the kernel keyring may be used as effective cache to avoid
        repeatedly asking users for passwords, if there are multiple
        objects that may be unlocked with the same password. The
        cached key will have a timeout of 2.5min set, after which it
        will be purged from the kernel keyring. Note that it is
        possible to cache multiple passwords under the same keyname,
        in which case they will be stored as NUL-separated list of
        passwords. Use
        <citerefentry project='die-net'><refentrytitle>keyctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        to access the cached key via the kernel keyring
        directly. Example: <literal>--keyname=cryptsetup</literal></para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--timeout=</option></term>

        <listitem><para>Specify the query timeout in seconds. Defaults
        to 90s. A timeout of 0 waits indefinitely. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--echo</option></term>

        <listitem><para>Echo the user input instead of masking it.
        This is useful when using
        <filename>systemd-ask-password</filename> to query for
        usernames. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--no-tty</option></term>

        <listitem><para>Never ask for password on current TTY even if
        one is available. Always use agent system.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--accept-cached</option></term>

        <listitem><para>If passed, accept cached passwords, i.e.
        passwords previously entered.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--multiple</option></term>

        <listitem><para>When used in conjunction with
        <option>--accept-cached</option> accept multiple passwords.
        This will output one password per line.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--no-output</option></term>

        <listitem><para>Do not print passwords to standard output.
        This is useful if you want to store a password in kernel
        keyring with <option>--keyname</option> but do not want it
        to show up on screen or in logs.</para></listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
    </variablelist>

  </refsect1>

  <refsect1>
    <title>Exit status</title>

    <para>On success, 0 is returned, a non-zero failure code
    otherwise.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-ask-password-console.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-tty-ask-password-agent</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>keyctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>plymouth</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>wall</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>