[systemd-devel] [PATCH 07/11] Support init=/bin/bash on the kernel command line

[Dr. Werner Fink]

On Fri, Jun 13, 2014 at 05:49:24PM +0200, Tom Gundersen wrote:
> On Fri, Jun 13, 2014 at 4:41 PM, Werner Fink <werner at suse.de> wrote:
> > From: Ruediger Oertel <ro at suse.de>
> >
> > Process 1 (aka init) needs to be started with an empty signal mask.
> > That includes the process 1 that's started after the initrd is finished.
> > When the initrd is using systemd (as it does with dracut based initrds)
> > then it is systemd that calls the real init.  Normally this is systemd
> > again, except when the user uses for instance "init=/bin/bash" on the
> > kernel command line.
> 
> Why is this necessary for /bin/bash, but not for /lib/systemd/systemd?
> Please include the explanation in the commit message.

I do not understand your question.  AFAIK the signal mask is set by
systemd accordingly to man:systemd.service(5) ... the only problem
with this schem is that /bin/bash nor any other shell does reset
its signal mask.  I guess that systemd will support the init=/bin/bash
on the kernel command line.  IMHO this requires a clean signal mask.

Werner


> > ---
> >  src/core/main.c |    9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git src/core/main.c src/core/main.c
> > index d5d1ee2..c082354 100644
> > --- src/core/main.c
> > +++ src/core/main.c
> > @@ -1831,6 +1831,7 @@ finish:
> >          if (reexecute) {
> >                  const char **args;
> >                  unsigned i, args_size;
> > +                sigset_t ss, o_ss;
> >
> >                  /* Close and disarm the watchdog, so that the new
> >                   * instance can reinitialize it, but doesn't get
> > @@ -1914,6 +1915,11 @@ finish:
> >                  args[i++] = NULL;
> >                  assert(i <= args_size);
> >
> > +                /* reenable any blocked signals, especially important
> > +                 * if we switch from initial ramdisk to init=... */
> > +                sigemptyset(&ss);
> > +                sigprocmask(SIG_SETMASK,&ss,&o_ss);
> > +
> >                  if (switch_root_init) {
> >                          args[0] = switch_root_init;
> >                          execv(args[0], (char* const*) args);
> > @@ -1932,6 +1938,9 @@ finish:
> >                          log_error("Failed to execute /bin/sh, giving up: %m");
> >                  } else
> >                          log_warning("Failed to execute /sbin/init, giving up: %m");
> > +
> > +                /* back to saved state if reexec failed */
> > +                sigprocmask(SIG_SETMASK,&o_ss,NULL);
> >          }
> >
> >          if (arg_serialization) {
> > --
> > 1.7.9.2

Werner

-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr
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