Re: Prevent shutdown with systemctl

From	<tomas@tuxteam.de>
Newsgroups	linux.debian.user
Subject	Re: Prevent shutdown with systemctl
Date	2016-01-04 22:20 +0100
Message-ID	<qNkHM-sc-9@gated-at.bofh.it> (permalink)
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On Mon, Jan 04, 2016 at 03:25:02PM -0500, Gary Dale wrote:
> On 04/01/16 12:14 PM, tomas@tuxteam.de wrote:

[...]

> >Dunno about systemctl, but FWIW you can't change the permissions of
> >a symlink. It's always "all on".
> >
> >
> Interesting. Why do they behave that way? Hard links don't (but
> replacing the symlink with a hardlink would fail if /bin & /sbin
> were on different devices. Also, I gather that systemctl looks at
> how it is called to determine the action it needs to take - would
> that create a problem if called from a hard link instead of a
> symlink?).

Perhaps I was a bit cavalier with my "all on": applications *doing* something
useful with a symlink reference it (except things like "rm", of course).

Thus, the permissions of the referenced-to file apply. Otherwise --
imagine: I do an ln -s /bin/bash $HOME, chmod u+w $HOME/bas
(since I own the link) and now have write access to the system shell?!

Hard links are a completely different kind of animal: they are
alternative directory entries for the same blob of data. Consequently,
there is no "primary" (as there is in symlinks). There are no
dangling hardlinks (unless your file system is corrupted).
As you can well imagine, some restrictions apply in the creation
of hardlinks:

  tomas@rasputin:~$ sudo useradd -m test
  [sudo] password for tomas: 
  tomas@rasputin:~$ ls -al /home/test
  total 20
  drwxr-xr-x 2 test test 4096 Jan  4 21:50 .
  drwxr-xr-x 9 root root 4096 Jan  4 21:50 ..
  -rw-r--r-- 1 test test  220 Apr 10  2010 .bash_logout
  -rw-r--r-- 1 test test 3392 Jul 13  2012 .bashrc
  -rw-r--r-- 1 test test  675 Apr 10  2010 .profile
  tomas@rasputin:~$ ln /home/test/.profile test-profile
  ln: failed to create hard link `test-profile' => `/home/test/.profile': Operation not permitted

Regards
- -- tomás
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Thread

Prevent shutdown with systemctl Floris <jkfloris@dds.nl> - 2016-01-04 17:00 +0100
  Re: Prevent shutdown with systemctl Michael Biebl <biebl@debian.org> - 2016-01-04 18:20 +0100
    Re: Prevent shutdown with systemctl Floris <jkfloris@dds.nl> - 2016-01-04 20:10 +0100
      Re: Prevent shutdown with systemctl Floris <jkfloris@dds.nl> - 2016-01-04 21:00 +0100
        Re: Prevent shutdown with systemctl Michael Biebl <biebl@debian.org> - 2016-01-04 21:20 +0100
      Re: Prevent shutdown with systemctl Brian <ad44@cityscape.co.uk> - 2016-01-04 21:50 +0100
        Re: Prevent shutdown with systemctl Floris <jkfloris@dds.nl> - 2016-01-04 23:50 +0100
          Re: Prevent shutdown with systemctl Michael Biebl <biebl@debian.org> - 2016-01-05 00:50 +0100
            Re: Prevent shutdown with systemctl Brian <ad44@cityscape.co.uk> - 2016-01-05 01:30 +0100
              Re: Prevent shutdown with systemctl Michael Biebl <biebl@debian.org> - 2016-01-05 01:40 +0100
  Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-04 18:20 +0100
    Re: Prevent shutdown with systemctl <tomas@tuxteam.de> - 2016-01-04 18:50 +0100
      Re: Prevent shutdown with systemctl Stuart Longland <stuartl@longlandclan.id.au> - 2016-01-04 21:20 +0100
        Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-04 21:40 +0100
          Re: Prevent shutdown with systemctl Stuart Longland <stuartl@longlandclan.id.au> - 2016-01-04 22:10 +0100
            Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-04 22:50 +0100
              Re: Prevent shutdown with systemctl Michael Biebl <biebl@debian.org> - 2016-01-05 01:20 +0100
                Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-05 18:20 +0100
      Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-04 21:30 +0100
        Re: Prevent shutdown with systemctl Stuart Longland <stuartl@longlandclan.id.au> - 2016-01-04 22:00 +0100
          Re: Prevent shutdown with systemctl David Wright <deblis@lionunicorn.co.uk> - 2016-01-05 05:50 +0100
        Re: Prevent shutdown with systemctl <tomas@tuxteam.de> - 2016-01-04 22:20 +0100
          Re: Prevent shutdown with systemctl Gary Dale <garydale@torfree.net> - 2016-01-04 22:50 +0100
            Re: Prevent shutdown with systemctl David Wright <deblis@lionunicorn.co.uk> - 2016-01-05 06:10 +0100
            Symlinks vs. hardlinks [was: Prevent shutdown with systemctl] <tomas@tuxteam.de> - 2016-01-05 09:40 +0100
              Re: Symlinks vs. hardlinks "Thomas Schmitt" <scdbackup@gmx.net> - 2016-01-05 11:10 +0100
                Re: Symlinks vs. hardlinks <tomas@tuxteam.de> - 2016-01-05 11:40 +0100
              Re: Symlinks vs. hardlinks [was: Prevent shutdown with systemctl] <tomas@tuxteam.de> - 2016-01-05 16:30 +0100
              Re: Symlinks vs. hardlinks [was: Prevent shutdown with systemctl] David Wright <deblis@lionunicorn.co.uk> - 2016-01-05 16:30 +0100
  Re: Prevent shutdown with systemctl Jude DaShiell <jdashiel@panix.com> - 2016-01-04 19:20 +0100
  Re: Prevent shutdown with systemctl Brian <ad44@cityscape.co.uk> - 2016-01-04 19:30 +0100
    Re: Prevent shutdown with systemctl jdd <jdd@dodin.org> - 2016-01-04 20:10 +0100
      Re: Prevent shutdown with systemctl jdd <jdd@dodin.org> - 2016-01-04 20:30 +0100
      Re: Prevent shutdown with systemctl Chris Bannister <cbannister@slingshot.co.nz> - 2016-01-05 11:10 +0100

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