nspawn: deprecate --share-system support

This removes the --share-system switch: from the documentation, the --help text
as well as the command line parsing. It's an ugly option, given that it kinda
contradicts the whole concept of PID namespaces that nspawn implements. Since
it's barely ever used, let's just deprecate it and remove it from the options.

It might be useful as a debugging option, hence the functionality is kept
around for now, exposed via an undocumented $SYSTEMD_NSPAWN_SHARE_SYSTEM
environment variable.

2 files changed, 10 insertions, 27 deletions

diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml
index 9b623c8353..97b348b565 100644
--- a/man/systemd-nspawn.xml
+++ b/man/systemd-nspawn.xml
@@ -274,8 +274,7 @@
         signals. It is recommended to use this mode to invoke arbitrary commands in containers, unless they have been
         modified to run correctly as PID 1. Or in other words: this switch should be used for pretty much all commands,
         except when the command refers to an init or shell implementation, as these are generally capable of running
-        correctly as PID 1. This option may not be combined with <option>--boot</option> or
-        <option>--share-system</option>.</para>
+        correctly as PID 1. This option may not be combined with <option>--boot</option>.</para>
         </listitem>
       </varlistentry>
 
@@ -285,8 +284,7 @@
 
         <listitem><para>Automatically search for an init binary and invoke it as PID 1, instead of a shell or a user
         supplied program. If this option is used, arguments specified on the command line are used as arguments for the
-        init binary. This option may not be combined with <option>--as-pid2</option> or
-        <option>--share-system</option>.</para>
+        init binary. This option may not be combined with <option>--as-pid2</option>.</para>
 
         <para>The following table explains the different modes of invocation and relationship to
         <option>--as-pid2</option> (see above):</para>
@@ -847,23 +845,6 @@
       </varlistentry>
 
       <varlistentry>
-        <term><option>--share-system</option></term>
-
-        <listitem><para>Allows the container to share certain system
-        facilities with the host. More specifically, this turns off
-        PID namespacing, UTS namespacing and IPC namespacing, and thus
-        allows the guest to see and interact more easily with
-        processes outside of the container. Note that using this
-        option makes it impossible to start up a full Operating System
-        in the container, as an init system cannot operate in this
-        mode. It is only useful to run specific programs or
-        applications this way, without involving an init system in the
-        container. This option implies <option>--register=no</option>.
-        This option may not be combined with
-        <option>--boot</option>.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
         <term><option>--register=</option></term>
 
         <listitem><para>Controls whether the container is registered
@@ -877,9 +858,7 @@
         and shown by tools such as
         <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
         If the container does not run an init system, it is
-        recommended to set this option to <literal>no</literal>. Note
-        that <option>--share-system</option> implies
-        <option>--register=no</option>. </para></listitem>
+        recommended to set this option to <literal>no</literal>.</para></listitem>
       </varlistentry>
 
       <varlistentry>
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 05e1fc1ab7..b7c2fe9e55 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -269,7 +269,6 @@ static void help(void) {
                "     --overlay-ro=PATH[:PATH...]:PATH\n"
                "                            Similar, but creates a read-only overlay mount\n"
                "  -E --setenv=NAME=VALUE    Pass an environment variable to PID 1\n"
-               "     --share-system         Share system namespaces with host\n"
                "     --register=BOOLEAN     Register container as machine\n"
                "     --keep-unit            Do not register a scope for the machine, reuse\n"
                "                            the service unit nspawn is running in\n"
@@ -405,7 +404,7 @@ static int parse_argv(int argc, char *argv[]) {
                 { "selinux-context",       required_argument, NULL, 'Z'                   },
                 { "selinux-apifs-context", required_argument, NULL, 'L'                   },
                 { "quiet",                 no_argument,       NULL, 'q'                   },
-                { "share-system",          no_argument,       NULL, ARG_SHARE_SYSTEM      },
+                { "share-system",          no_argument,       NULL, ARG_SHARE_SYSTEM      }, /* not documented */
                 { "register",              required_argument, NULL, ARG_REGISTER          },
                 { "keep-unit",             no_argument,       NULL, ARG_KEEP_UNIT         },
                 { "network-interface",     required_argument, NULL, ARG_NETWORK_INTERFACE },
@@ -814,6 +813,8 @@ static int parse_argv(int argc, char *argv[]) {
                         break;
 
                 case ARG_SHARE_SYSTEM:
+                        /* We don't officially support this anymore, except for compat reasons. People should use the
+                         * $SYSTEMD_NSPAWN_SHARE_SYSTEM environment variable instead. */
                         arg_share_system = true;
                         break;
 
@@ -1018,6 +1019,9 @@ static int parse_argv(int argc, char *argv[]) {
                         assert_not_reached("Unhandled option");
                 }
 
+        if (getenv_bool("SYSTEMD_NSPAWN_SHARE_SYSTEM") > 0)
+                arg_share_system = true;
+
         if (arg_share_system)
                 arg_register = false;
 
@@ -1025,7 +1029,7 @@ static int parse_argv(int argc, char *argv[]) {
                 arg_userns_chown = true;
 
         if (arg_start_mode != START_PID1 && arg_share_system) {
-                log_error("--boot and --share-system may not be combined.");
+                log_error("--boot and SYSTEMD_NSPAWN_SHARE_SYSTEM=1 may not be combined.");
                 return -EINVAL;
         }