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disable IPv6 debian

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  disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-15 13:50 +0200
    Re: disable IPv6 debian 황병희 <soyeomul@doraji.xyz> - 2022-04-15 14:00 +0200
      Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-15 14:30 +0200
        Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-15 17:00 +0200
          Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-15 18:00 +0200
            Re: disable IPv6 debian Tim Woodall <debianuser@woodall.me.uk> - 2022-04-15 18:10 +0200
          Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 02:10 +0200
            Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-16 02:20 +0200
              Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 02:30 +0200
                Re: disable IPv6 debian Charles Curley <charlescurley@charlescurley.com> - 2022-04-16 02:40 +0200
                Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-16 02:50 +0200
                  Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 03:10 +0200
                  Re: disable IPv6 debian The Wanderer <wanderer@fastmail.fm> - 2022-04-16 03:50 +0200
                    Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 04:10 +0200
                    Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-16 05:00 +0200
                      Re: disable IPv6 debian The Wanderer <wanderer@fastmail.fm> - 2022-04-16 14:10 +0200
                        Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-16 15:10 +0200
                        Re: disable IPv6 debian David Wright <deblis@lionunicorn.co.uk> - 2022-04-16 18:10 +0200
                    Re: disable IPv6 debian <tomas@tuxteam.de> - 2022-04-16 08:20 +0200
                      Re: disable IPv6 debian Tim Woodall <debianuser@woodall.me.uk> - 2022-04-16 08:40 +0200
                        Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 10:30 +0200
                          Re: disable IPv6 debian David <bouncingcats@gmail.com> - 2022-04-16 10:50 +0200
                          Re: disable IPv6 debian Greg Wooledge <greg@wooledge.org> - 2022-04-16 15:00 +0200
              Re: disable IPv6 debian Michael Stone <mstone@debian.org> - 2022-04-16 20:00 +0200
            Re: disable IPv6 debian <tomas@tuxteam.de> - 2022-04-16 08:20 +0200
        Re: disable IPv6 debian Chuck Zmudzinski <brchuckz@netscape.net> - 2022-04-15 19:40 +0200
        Re: disable IPv6 debian Andy Smith <andy@strugglers.net> - 2022-04-16 01:00 +0200
          Re: disable IPv6 debian didar <nosferatu@purlo.in> - 2022-04-16 07:10 +0200
            Re: disable IPv6 debian Andy Smith <andy@strugglers.net> - 2022-04-16 11:50 +0200
    Re: disable IPv6 debian Reco <recoverym4n@enotuniq.net> - 2022-04-15 14:30 +0200
      Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-15 14:40 +0200
        Re: disable IPv6 debian Erwan David <erwan@rail.eu.org> - 2022-04-15 16:00 +0200
          Re: disable IPv6 debian Jeremy Ardley <jeremy@ardley.org> - 2022-04-15 16:20 +0200
        Re: disable IPv6 debian Reco <recoverym4n@enotuniq.net> - 2022-04-15 16:20 +0200
    Re: disable IPv6 debian wilson <info@bigcount.xyz> - 2022-04-16 02:20 +0200
    Re: disable IPv6 debian Ash Joubert <ash@transient.nz> - 2022-04-16 02:20 +0200

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#247283

does bash shell have the list/array concept?

~$ list="1 2 3 4"

~$ for i in $list; do echo $i; done
1
2
3
4

is this a list access?

thanks

Tim Woodall wrote:
> But if you want to use grep, then you need -w at least. grep for pid 123

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#247284

On Sat, 16 Apr 2022 at 18:20, wilson <info@bigcount.xyz> wrote:

> does bash shell have the list/array concept?

Hi, this mailing list is very kind, and as part of that kindness
I want to offer you some kind advice.

First, no mailing list will have the
patience to teach you every feature of a programming
language, one question at a time.

So, here are two excellent websites for self-learning about shell
scripting:

https://www.shellcheck.net/

and

http://mywiki.wooledge.org/BashGuide
http://mywiki.wooledge.org/BashFAQ

wooledge.org will inform you, and shellcheck.net will correct and
advise improvements to any code that you paste into it.

Second, a good place to ask for help is on this mailing list
specifically for questions about shells and scripting:
  help-bash@gnu.org
which has archives here:
  https://lists.gnu.org/archive/html/help-bash/

Most of the people who give answers on that list are
extremely knowledgable about shell scripting.
That's not the case here. Shell scripting is hard,
and people who haven't spent a lot of time digging into
all the details often do not give good advice. The same is true
of the web, a lot of public shell examples are suboptimal
in some way.

Here's the answer to your question:
  http://mywiki.wooledge.org/BashGuide/Arrays

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#247290

On Sat, Apr 16, 2022 at 04:20:15PM +0800, wilson wrote:
> does bash shell have the list/array concept?

Bash has indexed arrays (since forever) and associative arrays (in
version 4.0 and above).

> ~$ list="1 2 3 4"
> 
> ~$ for i in $list; do echo $i; done
> 1
> 2
> 3
> 4
> 
> is this a list access?

That's a string, and an abuse of word-splitting.  It's a common
anti-pattern used in sh scripts, because sh doesn't have arrays or lists.
It "works" in this simple case, and in many other simple cases, where
the "list" elements are known-in-advance words that don't contain any
whitespace or globbing characters (and can't be the empty string).

It completely fails if the list elements contain any of those things.
Most notably, when the list elements are filenames, this approach is
doomed.

Here's how you would do it correctly in bash:

  list=(1 '' 2 'two and a half' 3 '3.14*' 4)

  for i in "${list[@]}"; do echo "<$i>"; done

The for loop can mostly be replaced by a single printf:

  printf '<%s>\n' "${list[@]}"

But there is one difference: if the array is empty (has zero elements),
the printf will still print one time, with an empty string as the
argument.  The for loop will not print anything at all.

See also:

https://mywiki.wooledge.org/BashGuide
https://mywiki.wooledge.org/BashFAQ/005

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#247301

On Fri, Apr 15, 2022 at 08:16:22PM -0400, Greg Wooledge wrote:
>ls -l .bashrc
>
>You've got a command name, and you're passing two string arguments to
>it.  If you feel a need to quote every string argument, then you should
>be writing it like this:
>
>ls "-l" ".bashrc"

There's nothing special about the command:

"ls" "-l" ".bashrc"

The key concept is that shell command lines *only* work on strings; unlike 
other languages, there's no "string" type that needs quotes and the only 
time you need do quotes is when dealing with special characters like 
spaces which would be interpreted differently without the quotes.

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#247280

[Multipart message — attachments visible in raw view] — view raw

On Sat, Apr 16, 2022 at 08:06:23AM +0800, wilson wrote:
> 
> 
> Greg Wooledge wrote:
> > if [ "$1" == on ]
> 
> this sounds strange. why a string doesn't need "" around in shell script?

Shell works by text substitution. If you have

  foo $bar $baz

the shell first replaces $bar and $baz by their values. Suppose bar is `123',
baz is `a multi-word string', then the next round is

  foo 123 a multi-word string

Then the shell splits the result in words, goes to look up `foo' in all the
places $PATH says it should look (yes, I've taken a HUGE shortcut here, chime
in to fill the voids ;-), and the command foo (say /usr/local/bin/foo) gets
to see four parameters: `123', `a', `multi-word' and `string'.

The quotes hold together things; different rules hold for single quotes (do
not substitute $vars) and double quotes (do substitute). So if you want to
invoke foo with two params, it is

  foo $bar "$baz"

If you don't know whether bar could contain a space and you also want to
have bar in one piece, better safe than sorry:

  foo "$bar" "$baz"

Text substitution systems were a thing in the 1970ies..1990ies. They do
have interesting properties, and survive in some odd places, the shells
being one (TeX, METAFONT, Tcl come to mind, too). And oh, the C preprocessor.

Cheers
-- 
t

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#247255

On 4/15/22 8:10 AM, wilson wrote:
> no. it's the Hadoop system, which has the possible issue with ipv6.
>
> thanks
>
>

I would check the documentation for Hadoop - does it have an option to 
disable ipv6? I would just disable ipv6 for the app that has the issue 
with ipv6, not for the whole system. I also note that according to the 
Debian Wiki, Debian does not provide Hadoop packages: 
https://wiki.debian.org/Hadoop

Regards,

Chuck

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#247261

Hello,

On Fri, Apr 15, 2022 at 10:34:25AM -0400, Chuck Zmudzinski wrote:
> I have an issue with a few websites that seem to hang with ipv6

If you happen to know their IPv6 addresses and can trust that those
assignments will remain stable then you may prefer instead to add
prohibited routes for these, e.g.

# ip route add prohibit 2001:db8::/32

Your web browser will then fall back to using the IPv4 results that
it gets from DNS.

Cheers,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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#247278

On Fri, Apr 15, 2022 at 10:58:01PM +0000, Andy Smith wrote:
> Hello,
> 
> On Fri, Apr 15, 2022 at 10:34:25AM -0400, Chuck Zmudzinski wrote:
> > I have an issue with a few websites that seem to hang with ipv6
> 
> If you happen to know their IPv6 addresses and can trust that those
> assignments will remain stable then you may prefer instead to add
> prohibited routes for these, e.g.

Not really. Y! uses both hardware load balancers as well as GSLB (global service
load balancing*). During routine maintenance and updates, both facilities are
used to move traffic to different targets.

> 
> # ip route add prohibit 2001:db8::/32
> 
> Your web browser will then fall back to using the IPv4 results that
> it gets from DNS.
> 
> Cheers,
> Andy
> 
> -- 
> https://bitfolk.com/ -- No-nonsense VPS hosting
> 


* uses DNS to point to different locations.
-- 
They just buzzed and buzzed...buzzed.

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#247287

Hello,

On Sat, Apr 16, 2022 at 10:39:03AM +0530, didar wrote:
> On Fri, Apr 15, 2022 at 10:58:01PM +0000, Andy Smith wrote:
> > If you happen to know their IPv6 addresses and can trust that those
> > assignments will remain stable then you may prefer instead to add
> > prohibited routes for these, e.g.
> 
> Not really. Y! uses both hardware load balancers as well as GSLB (global service
> load balancing*). During routine maintenance and updates, both facilities are
> used to move traffic to different targets.

Sure, it may not be feasible, but it is an alternative to manually
having to disable one's entire IPv6 connectivity and then re-enable
it later!

If you notice a problem with Y! (or whoever) then you may have
encountered a new netblock and at that time can just add another
prohibited route for it. There won't be many in total and it won't
matter if you pick a whole /32 or /29. v6 allocations are
purposefully intended to be huge so that organisations won't go back
for more and need extra routes in the global routing table.

Cheers,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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#247237

	Hi.

On Fri, Apr 15, 2022 at 07:32:01PM +0800, wilson wrote:
> What's the good way to disable IPv6 in a debian system?

The most non-intrusive way of doing it (side effects considered) is:

/sbin/sysctl -w net.ipv6.conf.default.disable_ipv6=1
/sbin/sysctl -w net.ipv6.conf.lo.disable_ipv6=0

Reco

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#247241

after doing this, do I need to restart the OS?

thanks

Reco wrote:
> The most non-intrusive way of doing it (side effects considered) is:
> 
> /sbin/sysctl -w net.ipv6.conf.default.disable_ipv6=1
> /sbin/sysctl -w net.ipv6.conf.lo.disable_ipv6=0

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#247242

Le 15/04/2022 à 14:35, wilson a écrit :
> after doing this, do I need to restart the OS?
> 
> thanks
> 
> Reco wrote:
>> The most non-intrusive way of doing it (side effects considered) is:
>>
>> /sbin/sysctl -w net.ipv6.conf.default.disable_ipv6=1
>> /sbin/sysctl -w net.ipv6.conf.lo.disable_ipv6=0
> 
> 

No. But it won't be kept if you reboot
To make it permanent you need to create the file
/etc/sysctl.d/10-disable_ipv6.conf with the 2 lines

net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=0

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#247243

[Multipart message — attachments visible in raw view] — view raw

On 15/4/22 9:59 pm, Erwan David wrote:
>
> No. But it won't be kept if you reboot
> To make it permanent you need to create the file
> /etc/sysctl.d/10-disable_ipv6.conf with the 2 lines
>
> net.ipv6.conf.default.disable_ipv6=1
> net.ipv6.conf.lo.disable_ipv6=0
>
>

However make sure no other file in /etc/sysctl.d is enabling ipv6. It 
would then come down to which script was executed last

e.g. if there was a 20-enable_ipv6.conf or similar.

-- 
Jeremy

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#247244

	Hi,

please do not top-post.

On Fri, Apr 15, 2022 at 08:35:33PM +0800, wilson wrote:
> Reco wrote:
> > The most non-intrusive way of doing it (side effects considered) is:
> > 
> > /sbin/sysctl -w net.ipv6.conf.default.disable_ipv6=1
> > /sbin/sysctl -w net.ipv6.conf.lo.disable_ipv6=0
> 
> after doing this, do I need to restart the OS?

No, you do not need to reboot. Moreover, those sysctls are
non-persistent, and that's intentional.
If you need to persist those settings, you'll need to modify
/etc/sysctl.conf or create a new file in /etc/sysctl.d.
Please consider reading sysctl.conf(5) *before* you touch those.

Reco

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#247263

Ash Joubert wrote:
> To completely and persistently disable all ipv6 support in the kernel, I 
> add "ipv6.disable=1" to the Linux command line variable 
> GRUB_CMDLINE_LINUX in /etc/default/grub, run update-grub, and reboot. If 
> you have other command line arguments, they are separated by whitespace.

Thanks.
how about adding sysctl commands in /etc/rc.local?

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#247264

On 15/04/2022 23:32, wilson wrote:
> What's the good way to disable IPv6 in a debian system?

To completely and persistently disable all ipv6 support in the kernel, I 
add "ipv6.disable=1" to the Linux command line variable 
GRUB_CMDLINE_LINUX in /etc/default/grub, run update-grub, and reboot. If 
you have other command line arguments, they are separated by whitespace.

Kind regards,

-- 
Ash Joubert <ash@transient.nz>
Director
Transient Software Limited <https://transient.nz/>
New Zealand

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