Re: ed

From	Lawrence D’Oliveiro <ldo@nz.invalid>
Newsgroups	comp.unix.shell
Subject	Re: ed
Date	2026-06-11 00:53 +0000
Organization	A noiseless patient Spider
Message-ID	<110d0v7$13kte$10@dont-email.me> (permalink)
References	<slrn112c9fb.2pa2.zaydm@new.localdomain> <1108b56$b00$1@nntp.sonologic.net> <1109qej$2vlaa$1@dont-email.me> <110abmr$ckmk$12@dont-email.me> <110cmrj$32trj$1@dont-email.me>

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On Wed, 10 Jun 2026 22:01:23 -0000 (UTC), John McCue wrote:

> On Wed, 10 Jun 2026 00:38:51 -0000 (UTC), Lawrence D’Oliveiro wrote:
>>
>> On Tue, 9 Jun 2026 19:44:19 -0000 (UTC), John McCue wrote:
>>
>>> There is one use for ed(1), when I boot NetBSD into single user
>>> mode, ed(1) is the only one available without jumping through
>>> hoops.
>>
>> Why is that? Is it because NetBSD still has the legacy
>> root-versus-usr separation of executables and libraries?
>
> From what I have seen, seems Linux does not have a real single user
> mode.

There is no “real single user mode” in any *nix. The concept of
single/multi-user mode is irrelevant to the kernel.

> NetBSD and the other BSDs have real single user mode where no file
> systems are mounted, no daemons are started and root is mounted RO.

You contradict yourself by saying “no file systems are mounted” and
then that “root is mounted RO”. Which is it?

There must *always* be a filesystem mounted on / on every *nix OS
worthy of the name -- surely even the BSDs. On Linux, this is
initially initrd (the “initial RAM disk”) which contains some minimal
code, scripts etc sufficient to find and mount the real root, as
specified in the parameters passed across from the boot loader.

But when switching over, then you can’t just unmount the existing root
filesystem, because after all it is the root filesystem. So you mount
the new root in a temporary directory, and use a special system call
“pivot_root” <https://manpages.debian.org/pivot_root(2)>, to switch
their places around. Now when you unmount the directory where the new
root was previously mounted, it is actually the initrd you’re
unmounting.

As per the man page, pivot_root doesn’t just play a role at boot time,
it is also useful in the setup of filesystem namespaces for containers
etc.

> NetBSD boots into /bin/sh or a shell of your choice and you work
> from that, no login needed. Also I think only static executables are
> available for use.

On Linux, there is the option to specify the word “single” among the
boot parameters. This is a signal to the init process to pause the
startup of regular services and spawn a shell; if/when this
terminates, it continues with the full startup, including mounting of
non-root filesystem volumes. (Note the kernel itself assigns no
meaning to this boot parameter).

One recent time I tried this, it insisted in asking for the root
password before giving me shell access (could have been just that
distro). But another option that should bypass this is a boot
parameter setting like like “init=/bin/bash” -- this tells the kernel
to run something other than the usual /sbin/init as PID 1. This
disables the normal userland startup process altogether.

But then, you could continue the normal startup with the command
“exec /sbin/init”. Or, of course, terminate the shell, which will
trigger a reboot.

> I do not know what "legacy root-versus-usr" means, I would never
> want a system that does not have a clear separation between root and
> users.

Why, do you still keep user directories in /usr?

Thread

ed __ ___ ________ ____ ______. Zayd Mohammed <zaydm@172.24.208.1> - 2026-06-08 02:16 +0000
  Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-08 04:46 +0200
    Re: ed __ ___ ________ ____ ______. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-08 13:44 +0000
      Re: ed __ ___ ________ ____ ______. gazelle@shell.xmission.com (Kenny McCormack) - 2026-06-08 14:12 +0000
        Re: ed. cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-08 19:30 +0000
      Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-08 14:40 -0700
        Re: ed __ ___ ________ ____ ______. groenveld@acm.org (John D Groenveld) - 2026-06-09 00:04 +0000
        Re: ed __ ___ ________ ____ ______. Adam Sampson <ats@offog.org> - 2026-06-09 01:50 +0100
        Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-09 16:47 +0200
          Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-09 16:41 -0700
      Re: ed __ ___ ________ ____ ______. Ben Collver <bencollver@tilde.pink> - 2026-06-09 14:27 +0000
    Re: ed __ ___ ________ ____ ______. Eric Pozharski <apple.universe@posteo.net> - 2026-06-08 22:28 +0000
    Re: ed __ ___ ________ ____ ______. Lumin Etherlight <lumin+usenet@etherlight.link> - 2026-06-09 03:25 +0300
      Re: ed __ ___ ________ ____ ______. Daniel Cerqueira <dan.list@lispclub.com> - 2026-06-09 09:47 +0100
        Re: ed __ ___ ________ ____ ______. Joerg Mertens <joerg-mertens@t-online.de> - 2026-06-09 15:53 +0200
          Re: ed __ ___ ________ ____ ______. Daniel Cerqueira <dan.list@lispclub.com> - 2026-06-09 21:00 +0100
          Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-09 16:29 -0700
            Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-11 08:39 +0200
              Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-11 13:40 -0700
                Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-12 16:56 +0200
                Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-12 15:22 -0700
                Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-13 00:58 +0200
          Re: ed __ ___ ________ ____ ______. Daniel Cerqueira <dan.list@lispclub.com> - 2026-07-03 00:55 +0100
            Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-07-03 00:47 +0000
              Re: ed John McCue <jmclnx@gmail.com.invalid> - 2026-07-03 01:32 +0000
                Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-07-03 04:11 +0000
                Re: ed Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-03 07:57 +0100
                Re: ed Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-07-03 09:32 +0200
            Re: ed __ ___ ________ ____ ______. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-07-02 20:30 -0700
      Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-09 17:57 +0200
  Re: ed __ ___ ________ ____ ______. John McCue <jmclnx@gmail.com.invalid> - 2026-06-08 22:57 +0000
  Re: ed __ ___ ________ ____ ______. Lumin Etherlight <lumin+usenet@etherlight.link> - 2026-06-09 03:02 +0300
  Re: ed __ ___ ________ ____ ______. gmc@metro.cx (Koen Martens) - 2026-06-09 06:17 +0000
    Re: ed __ ___ ________ ____ ______. Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-09 06:55 +0000
    Re: ed __ ___ ________ ____ ______. John McCue <jmclnx@gmail.com.invalid> - 2026-06-09 19:44 +0000
      Re: ed __ ___ ________ ____ ______. Top Dead Ctr <tdc@invalid.invalid> - 2026-06-09 14:09 -0600
      Re: ed __ ___ ________ ____ ______. Christian Weisgerber <naddy@mips.inka.de> - 2026-06-09 23:52 +0000
        Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-10 00:40 +0000
      Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-10 00:38 +0000
        Re: ed John McCue <jmclnx@gmail.com.invalid> - 2026-06-10 22:01 +0000
          Re: ed Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-10 16:43 -0700
            Re: ed Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-10 16:50 -0700
            Re: ed cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-10 23:53 +0000
              Re: ed Eli the Bearded <*@eli.users.panix.com> - 2026-06-11 00:12 +0000
                Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-11 00:55 +0000
                Re: ed cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-11 02:00 +0000
                Re: ed Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-10 19:30 -0700
                Re: ed cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-11 11:31 +0000
                Re: ed Christian Weisgerber <naddy@mips.inka.de> - 2026-06-11 15:02 +0000
              Re: ed Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-11 08:46 +0200
            Re: ed John McCue <jmclnx@gmail.com.invalid> - 2026-06-11 14:28 +0000
          Re: ed cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-10 23:48 +0000
          Re: ed Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2026-06-11 00:24 +0000
            Re: ed John McCue <jmclnx@gmail.com.invalid> - 2026-06-11 14:11 +0000
              Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-12 00:22 +0000
          Re: ed Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-11 00:53 +0000
            Re: ed Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-11 09:02 +0200
    Re: ed __ ___ ________ ____ ______. Nuno Silva <nunojsilva@invalid.invalid> - 2026-06-10 11:03 +0100
      Re: ed __ ___ ________ ____ ______. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-11 09:12 +0200
        Re: ed __ ___ ________ ____ ______. Nuno Silva <nunojsilva@invalid.invalid> - 2026-06-12 09:44 +0100
          Android editor (Was: ed __ ___ ________ ____ ______.) gazelle@shell.xmission.com (Kenny McCormack) - 2026-06-12 09:03 +0000
            Re: Android editor Nuno Silva <nunojsilva@invalid.invalid> - 2026-06-12 12:01 +0100

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