Re: The boring Linux habit that saves machines

From	TheLastSysop <thelastsysop@dev.null>
Newsgroups	comp.os.linux.misc
Subject	Re: The boring Linux habit that saves machines
Date	2026-06-06 11:12 +0000
Organization	The Null Device Restoration Society
Message-ID	<67bea2dbebca296b0531@dev.null> (permalink)
References	(6 earlier) <c666a26d150d22509e46@dev.null> <1100na0$1nk20$3@dont-email.me> <h48dfmxig7.ln2@Telcontar.valinor> <8af2d73348d22ad1e78d@dev.null> <bibdfmxgb4.ln2@Telcontar.valinor>

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>On Sat, 6 Jun 2026 13:06:19 +0200, "Carlos E.R." <robin_listas@es.invalid>
>wrote:
>On 2026-06-06 12:14, TheLastSysop wrote:
>>> On Sat, 6 Jun 2026 12:07:45 +0200, "Carlos E.R." <robin_listas@es.invalid>
>>> wrote:
>>> On 2026-06-06 10:55, Lawrence D’Oliveiro wrote:
>>>> On Sun, 31 May 2026 07:46:12 GMT, TheLastSysop wrote:
>>>>
>>>>> Before any mirroring run, I like a preflight that proves the
>>>>> destination is really mounted and is the expected filesystem, not
>>>>> just an empty directory that happens to exist.
>>>>
>>>> Been there, done that. The simple fix is to make the mount-point
>>>> directory read-only. That puts a stop to any attempts to put stuff in
>>>> there without the actual volume being present.
>>>
>>> That simple? Does this work? Wow.
>>
>> It helps, but I would still treat it as a guard rail rather than the whole
>> check.
>>
>> If the mirroring job runs as an ordinary user, a read-only mount-point will
>> usually catch the "disk not mounted, writing into the empty directory" case
>> nicely.  If the job runs as root, root can still write there unless you add
>> something else, and some tools may change permissions as part of their work.
>>
>> For scripts I like both pieces:
>>
>>      findmnt -rn --target /backup >/dev/null || exit 1
>>
>> and, if appropriate, check the expected source/device or fstype too.  The
>> read-
>> only mount-point is a good extra tripwire, but findmnt/mountpoint makes the
>> failure mode explicit before rsync or cp gets anywhere near the tree.
>>
>
>In my scripts, I always check that destination is mounted.
>
>Maybe "mount | grep destination"

Yes, that is the important part: make the script prove the destination is
mounted before it starts copying.

I would avoid plain "mount | grep destination" if the script matters, though. It
is easy to get a false match, a quoting problem, or a surprise when the path
contains characters grep treats as interesting.  It also answers a slightly
fuzzy question: "does this text appear in mount output?"

I prefer asking the mount table the exact question:

    findmnt -rn --target /backup >/dev/null || exit 1

or, for the simple case:

    mountpoint -q /backup || exit 1

Then add checks for fstype/source if mounting the wrong disk would be just as
bad as mounting no disk.

-- 
TheLastSysop <thelastsysop@dev.null>
"I survived the great rm -rf / rehearsal and all I got was this .signature."

Thread

The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-30 22:28 +0000
  Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-05-30 23:51 -0400
    Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-31 04:23 +0000
      Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-05-31 02:26 -0400
        Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-31 06:41 +0000
          Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-05-31 03:37 -0400
            Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-31 07:46 +0000
              Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 08:55 +0000
                Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 12:07 +0200
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 10:14 +0000
                Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 13:06 +0200
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 11:12 +0000
                Re: The boring Linux habit that saves machines Rich <rich@example.invalid> - 2026-06-06 18:30 +0000
                Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 20:49 +0200
          Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 09:07 +0000
          Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 09:10 +0000
      Re: The boring Linux habit that saves machines Anssi Saari <anssi.saari@usenet.mail.kapsi.fi> - 2026-06-01 12:20 +0300
        Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-01 09:38 +0000
          Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-02 02:20 -0400
            Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-02 11:08 +0000
              Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-02 23:58 -0400
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-04 11:47 +0000
                Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-04 11:57 -0400
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-05 12:53 +0000
                Re: The boring Linux habit that saves machines Richard Kettlewell <invalid@invalid.invalid> - 2026-06-05 17:35 +0100
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-05 16:42 +0000
                Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-06 00:06 -0400
                Re: The boring Linux habit that saves machines Richard Kettlewell <invalid@invalid.invalid> - 2026-06-06 10:35 +0100
                Re: The boring Linux habit that saves machines The Natural Philosopher <tnp@invalid.invalid> - 2026-06-06 10:39 +0100
                Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-05 23:55 -0400
                Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 09:40 +0000
                Re: The boring Linux habit that saves machines Rich <rich@example.invalid> - 2026-06-06 18:42 +0000
              Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 08:53 +0000
          Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 08:52 +0000
      Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 06:41 +0000
        Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-06 03:07 -0400
          Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 13:28 +0200
          Re: The boring Linux habit that saves machines rbowman <bowman@montana.com> - 2026-06-06 19:16 +0000
        Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 09:40 +0000
  Re: The boring Linux habit that saves machines "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2026-05-31 16:43 +0800
    Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-31 08:48 +0000
    Re: The boring Linux habit that saves machines Stéphane CARPENTIER <sc@fiat-linux.fr> - 2026-05-31 10:16 +0000
      Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-05-31 10:22 +0000
  Re: The boring Linux habit that saves machines Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-06 06:38 +0000
    Re: The boring Linux habit that saves machines c186282 <c186282@nnada.net> - 2026-06-06 03:04 -0400
      Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 13:32 +0200
        Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 11:34 +0000
          Re: The boring Linux habit that saves machines "Carlos E.R." <robin_listas@es.invalid> - 2026-06-06 14:01 +0200
    Re: The boring Linux habit that saves machines Nuno Silva <nunojsilva@invalid.invalid> - 2026-06-06 09:17 +0100
      Re: The boring Linux habit that saves machines TheLastSysop <thelastsysop@dev.null> - 2026-06-06 09:40 +0000

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