bwrap.xml

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<refentry id="bwrap">

<refentryinfo>
  <title>bwrap</title>
  <productname>Project Atomic</productname>
  <authorgroup>
    <author>
      <contrib>Developer</contrib>
      <firstname>Alexander</firstname>
      <surname>Larsson</surname>
    </author>
    <author>
      <contrib>Developer</contrib>
      <firstname>Colin</firstname>
      <surname>Walters</surname>
    </author>
  </authorgroup>
</refentryinfo>

<refmeta>
  <refentrytitle>bwrap</refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo class="manual">User Commands</refmiscinfo>
</refmeta>

<refnamediv>
  <refname>bwrap</refname>
  <refpurpose>container setup utility</refpurpose>
</refnamediv>

<refsynopsisdiv>
<cmdsynopsis>
<command>bwrap</command>
<arg choice="opt" rep="repeat"><replaceable>OPTION</replaceable></arg>
<arg choice="opt"><replaceable>COMMAND</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1><title>Description</title>
<para>
  <command>bwrap</command> is a privileged helper for container setup. You
  are unlikely to use it directly from the commandline, although that is possible.
</para>
<para>
  It works by creating a new, completely empty, filesystem namespace where the root
  is on a tmpfs that is invisible from the host, and which will be automatically
  cleaned up when the last process exits. You can then use commandline options to
  construct the root filesystem and process environment for the command to run in
  the namespace.
</para>
<para>
  By default, <command>bwrap</command> creates a new mount namespace for the sandbox.
  Optionally it also sets up new user, ipc, pid, network and uts namespaces (but note the
  user namespace is required if bwrap is not installed setuid root).
  The application in the sandbox can be made to run with a different UID and GID.
</para>
<para>
  If needed (e.g. when using a PID namespace) <command>bwrap</command>
  is running a minimal pid 1 process in the sandbox that is
  responsible for reaping zombies. It also detects when the initial
  application process (pid 2) dies and reports its exit status back to
  the original spawner.  The pid 1 process exits to clean up the
  sandbox when there are no other processes in the sandbox left.
</para>
</refsect1>

<refsect1><title>Options</title>
  <para>
    When options are used multiple times, the last option wins, unless otherwise
    specified.
  </para>
  <para>General options:</para>
  <variablelist>
    <varlistentry>
      <term><option>--help</option></term>
      <listitem><para>Print help and exit</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--version</option></term>
      <listitem><para>Print version</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--args <arg choice="plain">FD</arg></option></term>
      <listitem><para>
        Parse nul-separated arguments from the given file descriptor.
        This option can be used multiple times to parse options from
        multiple sources.
      </para></listitem>
    </varlistentry>
  </variablelist>
  <para>Options related to kernel namespaces:</para>
  <variablelist>
    <varlistentry>
      <term><option>--unshare-user</option></term>
      <listitem><para>Create a new user namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-user-try</option></term>
      <listitem><para>Create a new user namespace if possible else skip it</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-ipc</option></term>
      <listitem><para>Create a new ipc namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-pid</option></term>
      <listitem><para>Create a new pid namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-net</option></term>
      <listitem><para>Create a new network namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-uts</option></term>
      <listitem><para>Create a new uts namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-cgroup</option></term>
      <listitem><para>Create a new cgroup namespace</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-cgroup-try</option></term>
      <listitem><para>Create a new cgroup namespace if possible else skip it</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unshare-all</option></term>
      <listitem><para>Unshare all possible namespaces. Currently equivalent with: <option>--unshare-user-try</option> <option>--unshare-ipc</option> <option>--unshare-pid</option> <option>--unshare-net</option> <option>--unshare-uts</option> <option>--unshare-cgroup-try</option></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--userns <arg choice="plain">FD</arg></option></term>
      <listitem><para>Use an existing user namespace instead of creating a new one. The namespace must fulfil the permission requirements for setns(), which generally means that it must be a decendant of the currently active user namespace, owned by the same user. </para>
      <para>This is incompatible with --unshare-user, and doesn't work in the setuid version of bubblewrap.</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--userns2 <arg choice="plain">FD</arg></option></term>
      <listitem><para>After setting up the new namespace, switch into the specified namespace. For this to work the specified namespace must be a decendant of the user namespace used for the setup, so this is only useful in combination with --userns.</para>
      <para>This is useful because sometimes bubblewrap itself creates nested user namespaces (to work around some kernel issues) and --userns2 can be used to enter these.</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--pidns <arg choice="plain">FD</arg></option></term>
      <listitem><para>Use an existing pid namespace instead of creating one. This is often used with --userns, because the pid namespace must be owned by the same user namespace that bwrap uses. </para>
      <para>Note that this can be combined with --unshare-pid, and in that case it means that the sandbox will be in its own pid namespace, which is a child of the passed in one.</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--uid <arg choice="plain">UID</arg></option></term>
      <listitem><para>Use a custom user id in the sandbox (requires <option>--unshare-user</option>)</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--gid <arg choice="plain">GID</arg></option></term>
      <listitem><para>Use a custom group id in the sandbox (requires <option>--unshare-user</option>)</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--hostname <arg choice="plain">HOSTNAME</arg></option></term>
      <listitem><para>Use a custom hostname in the sandbox (requires <option>--unshare-uts</option>)</para></listitem>
    </varlistentry>
  </variablelist>
  <para>Options about environment setup:</para>
  <variablelist>
    <varlistentry>
      <term><option>--chdir <arg choice="plain">DIR</arg></option></term>
      <listitem><para>Change directory to <arg choice="plain">DIR</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--setenv <arg choice="plain">VAR</arg> <arg choice="plain">VALUE</arg></option></term>
      <listitem><para>Set an environment variable</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--unsetenv <arg choice="plain">VAR</arg></option></term>
      <listitem><para>Unset an environment variable</para></listitem>
    </varlistentry>
  </variablelist>
  <para>Options for monitoring the sandbox from the outside:</para>
  <variablelist>
    <varlistentry>
      <term><option>--lock-file <arg choice="plain">DEST</arg></option></term>
      <listitem><para>
        Take a lock on <arg choice="plain">DEST</arg> while the sandbox is running.
        This option can be used multiple times to take locks on multiple files.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--sync-fd <arg choice="plain">FD</arg></option></term>
      <listitem><para>Keep this file descriptor open while the sandbox is running</para></listitem>
    </varlistentry>
  </variablelist>
  <para>
    Filesystem related options. These are all operations that modify the filesystem directly, or
    mounts stuff in the filesystem. These are applied in the order they are given as arguments.
    Any missing parent directories that are required to create a specified destination are
    automatically created as needed.
  </para>
  <variablelist>
    <varlistentry>
      <term><option>--bind <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Bind mount the host path <arg choice="plain">SRC</arg> on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--bind-try <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Equal to <option>--bind</option> but ignores non-existent <arg choice="plain">SRC</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--dev-bind <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Bind mount the host path <arg choice="plain">SRC</arg> on <arg choice="plain">DEST</arg>, allowing device access</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--dev-bind-try <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Equal to <option>--dev-bind</option> but ignores non-existent <arg choice="plain">SRC</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--ro-bind <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Bind mount the host path <arg choice="plain">SRC</arg> readonly on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--ro-bind-try <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Equal to <option>--ro-bind</option> but ignores non-existent <arg choice="plain">SRC</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--remount-ro <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Remount the path <arg choice="plain">DEST</arg> as readonly.  It works only on the specified mount point, without changing any other mount point under the specified path</para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--proc <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Mount procfs on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--dev <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Mount new devtmpfs on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--tmpfs <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Mount new tmpfs on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--mqueue <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Mount new mqueue on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--dir <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Create a directory at <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--file <arg choice="plain">FD</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Copy from the file descriptor <arg choice="plain">FD</arg> to <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--bind-data <arg choice="plain">FD</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Copy from the file descriptor <arg choice="plain">FD</arg> to a file which is bind-mounted on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--ro-bind-data <arg choice="plain">FD</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Copy from the file descriptor <arg choice="plain">FD</arg> to a file which is bind-mounted readonly on <arg choice="plain">DEST</arg></para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--symlink <arg choice="plain">SRC</arg> <arg choice="plain">DEST</arg></option></term>
      <listitem><para>Create a symlink at <arg choice="plain">DEST</arg> with target <arg choice="plain">SRC</arg></para></listitem>
    </varlistentry>
  </variablelist>
  <para>Lockdown options:</para>
  <variablelist>
    <varlistentry>
      <term><option>--seccomp <arg choice="plain">FD</arg></option></term>
      <listitem><para>
        Load and use seccomp rules from <arg choice="plain">FD</arg>.
        The rules need to be in the form of a compiled eBPF program,
        as generated by seccomp_export_bpf.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--exec-label <arg choice="plain">LABEL</arg></option></term>
      <listitem><para>
	Exec Label from the sandbox. On an SELinux system you can specify the SELinux
	context for the sandbox process(s).
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--file-label <arg choice="plain">LABEL</arg></option></term>
      <listitem><para>
	File label for temporary sandbox content. On an SELinux system you can specify
	the SELinux context for the sandbox content.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--block-fd <arg choice="plain">FD</arg></option></term>
      <listitem><para>
	Block the sandbox on reading from FD until some data is available.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--userns-block-fd <arg choice="plain">FD</arg></option></term>
      <listitem><para>
	Do not initialize the user namespace but wait on FD until it is ready.  This allow
        external processes (like newuidmap/newgidmap) to setup the user namespace before it
        is used by the sandbox process.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--info-fd <arg choice="plain">FD</arg></option></term>
      <listitem><para>
	Write information in JSON format about the sandbox to FD.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--new-session</option></term>
      <listitem><para>
	Create a new terminal session for the sandbox (calls setsid()). This
        disconnects the sandbox from the controlling terminal which means
        the sandbox can't for instance inject input into the terminal.
        </para><para>
        Note: In a general sandbox, if you don't use --new-session, it is
        recommended to use seccomp to disallow the TIOCSTI ioctl, otherwise
        the application can feed keyboard input to the terminal.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--die-with-parent</option></term>
      <listitem><para>
    Ensures child process (COMMAND) dies when bwrap's parent dies. Kills (SIGKILL)
        all bwrap sandbox processes in sequence from parent to child
        including COMMAND process when bwrap or bwrap's parent dies.
        See prctl, PR_SET_PDEATHSIG.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--as-pid-1</option></term>
      <listitem><para>
	Do not create a process with PID=1 in the sandbox to reap child processes.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--cap-add <arg choice="plain">CAP</arg></option></term>
      <listitem><para>
        Add the specified capability when running as privileged user.  It accepts
        the special value ALL to add all the permitted caps.
      </para></listitem>
    </varlistentry>
    <varlistentry>
      <term><option>--cap-drop <arg choice="plain">CAP</arg></option></term>
      <listitem><para>
        Drop the specified capability when running as privileged user.  It accepts
        the special value ALL to drop all the caps.

        By default no caps are left in the sandboxed process.  The
        <option>--cap-add</option> and <option>--cap-drop</option>
        options are processed in the order they are specified on the
        command line.  Please be careful to the order they are specified.
      </para></listitem>
    </varlistentry>
  </variablelist>
</refsect1>

<refsect1>
  <title>Environment</title>

  <variablelist>
    <varlistentry>
      <term><envar>HOME</envar></term>
      <listitem><para>
        Used as the cwd in the sandbox if <option>--chdir</option> has not been
        explicitly specified and the current cwd is not present inside the sandbox.
        The <option>--setenv</option> option can be used to override the value
        that is used here.
      </para></listitem>
    </varlistentry>
  </variablelist>
</refsect1>

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

  <para>
    The <command>bwrap</command> command returns the exit status of the
    initial application process (pid 2 in the sandbox).
  </para>
</refsect1>

</refentry>