Examples of local-host-entries or hosts-service-type?

Examples of local-host-entries or hosts-service-type?

[Sergiu Ivanov]

Hello Guix,

I am reconfiguring my system right now, and guix system reconfigure
/etc/config.scm tells me this:

/etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
/etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
/etc/config.scm:124:14: warning: the 'hosts-file' field is deprecated, please use 'hosts-service-type' instead

For the record, here are the lines guix system reconfigure is
complaining about:

(hosts-file (plain-file "hosts"
			(string-append
			 (local-host-aliases host-name)
			 "some.ip.address.1 machine1\n"
			 "some.other.ip.address machine2\n")))

I spent quite some time trying to find some examples of using
local-host-entries or hosts-service-type, but I don't seem to find any
mention of these.  Quite on the contrary, the Guix manual actually seems
to advice declarations similar to those which I have in my
/etc/config.scm.

Could someone point me to an example of how I should update
my configuration?

-
Sergiu

Re: Examples of local-host-entries or hosts-service-type?

[Bruno Victal]

On 2023-02-10 22:40, Sergiu Ivanov wrote:
> Hello Guix,
> 
> I am reconfiguring my system right now, and guix system reconfigure
> /etc/config.scm tells me this:
> 
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:124:14: warning: the 'hosts-file' field is deprecated, please use 'hosts-service-type' instead
> 
> For the record, here are the lines guix system reconfigure is
> complaining about:
> 
> (hosts-file (plain-file "hosts"
> 			(string-append
> 			 (local-host-aliases host-name)
> 			 "some.ip.address.1 machine1\n"
> 			 "some.other.ip.address machine2\n")))
> 
> I spent quite some time trying to find some examples of using
> local-host-entries or hosts-service-type, but I don't seem to find any
> mention of these.  Quite on the contrary, the Guix manual actually seems
> to advice declarations similar to those which I have in my
> /etc/config.scm.
> 
> Could someone point me to an example of how I should update
> my configuration?
> 
> -
> Sergiu
> 

See 'hosts-service-type' under Service Reference <https://guix.gnu.org/en/manual/devel/en/html_node/Service-Reference.html>.


Cheers,
Bruno

Re: Examples of local-host-entries or hosts-service-type?

[Remco van 't Veer]

Hi Sergiu,

2023/02/10 23:40, Sergiu Ivanov:

> Hello Guix,
>
> I am reconfiguring my system right now, and guix system reconfigure
> /etc/config.scm tells me this:
>
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:124:14: warning: the 'hosts-file' field is deprecated, please use 'hosts-service-type' instead
>
> For the record, here are the lines guix system reconfigure is
> complaining about:
>
> (hosts-file (plain-file "hosts"
> 			(string-append
> 			 (local-host-aliases host-name)
> 			 "some.ip.address.1 machine1\n"
> 			 "some.other.ip.address machine2\n")))
>
> I spent quite some time trying to find some examples of using
> local-host-entries or hosts-service-type, but I don't seem to find any
> mention of these.  Quite on the contrary, the Guix manual actually seems
> to advice declarations similar to those which I have in my
> /etc/config.scm.
>
> Could someone point me to an example of how I should update
> my configuration?

In the guix manual I found this:

  https://guix.gnu.org/en/manual/devel/en/html_node/Service-Reference.html#index-hosts_002dservice_002dtype

So instead of using (hosts-file ..) you'll have to use
(hosts-service-type ..) instead, as you already mentioned.  You'll end
up with something like to following:

  (operating-system
    ;; ...

    (essential-services
     (modify-services
         (operating-system-default-essential-services this-operating-system)
       (hosts-service-type config =>
                           (cons* (host "some.ip.address.1" "machine1")
                                  (host "some.other.ip.address" "machine2")
                                  (local-host-entries host-name)))))

    ;; ...

I tried it and it seems to work for me.  Also, I agree the documentation
needs some love here.

Cheers,
Remco

Re: Examples of local-host-entries or hosts-service-type?

[Sergiu Ivanov]

Hi Bruno, hi Remco,

Thank you very much for your suggestions!


Remco van 't Veer <remco@remworks.net> [2023-02-11T12:46:35+0100]:
> 2023/02/10 23:40, Sergiu Ivanov:
>>
>> Could someone point me to an example of how I should update
>> my configuration?
>
> In the guix manual I found this:
>
>   https://guix.gnu.org/en/manual/devel/en/html_node/Service-Reference.html#index-hosts_002dservice_002dtype
>
> So instead of using (hosts-file ..) you'll have to use
> (hosts-service-type ..) instead, as you already mentioned.  You'll end
> up with something like to following:
>
>   (operating-system
>     ;; ...
>
>     (essential-services
>      (modify-services
>          (operating-system-default-essential-services this-operating-system)
>        (hosts-service-type config =>
>                            (cons* (host "some.ip.address.1" "machine1")
>                                   (host "some.other.ip.address" "machine2")
>                                   (local-host-entries host-name)))))
>
>     ;; ...

Oh, thank you very much for the specific solution!  It worked for
me flawlessly.

Actually, where did you get local-host-entries from?  The documentation
page you and Bruno cite doesn't seem to ever mention this function :O
Unless I am looking at some old version of the docs.

> Also, I agree the documentation needs some love here.

I am willing to contribute.  What would be the best place to do changes
to the documentation?

I would follow this mini-roadmap:

1. Add the explanation of local-host-entries to
   https://guix.gnu.org/en/manual/devel/en/html_node/Service-Reference.html#index-hosts_002dservice_002dtype

2. Say here
   https://guix.gnu.org/manual/en/html_node/operating_002dsystem-Reference.html
   that hosts-file is deprecated.

3. Update the examples here to use hosts-service-type instead of
   hosts-file: https://guix.gnu.org/manual/en/guix.html

What do you think?

I've never submitted a patch to Guix docs before, so all suggestions and
hints are welcome :-)

-
Sergiu

Re: Examples of local-host-entries or hosts-service-type?

[Remco van 't Veer]

Hi Sergiu,

2023/02/13 11:49, Sergiu Ivanov:

> Actually, where did you get local-host-entries from?  The documentation
> page you and Bruno cite doesn't seem to ever mention this function :O
> Unless I am looking at some old version of the docs.

To be honest, I did not know about local-host-entries before your email
and thought it would allow me to cleanup my own (operating-system
.. (hosts-file (plain-file .. (string-append ..) mess.  So I did some
digging in the guix source and found some references in gnu/system.scm.

>> Also, I agree the documentation needs some love here.
>
> I am willing to contribute.  What would be the best place to do changes
> to the documentation?

doc/guix.texi

> I would follow this mini-roadmap:
>
> 1. Add the explanation of local-host-entries to
>    https://guix.gnu.org/en/manual/devel/en/html_node/Service-Reference.html#index-hosts_002dservice_002dtype
>
> 2. Say here
>    https://guix.gnu.org/manual/en/html_node/operating_002dsystem-Reference.html
>    that hosts-file is deprecated.
>
> 3. Update the examples here to use hosts-service-type instead of
>    hosts-file: https://guix.gnu.org/manual/en/guix.html
>
> What do you think?

Sounds like a plan to me.  Note: all the above is part of doc/guix.texi,
I think.

> I've never submitted a patch to Guix docs before, so all suggestions and
> hints are welcome :-)

Me neither (apart from a typo I found in the Service Reference section
during grepping for examples).  I don't have a clue about how
translations are kept in sync.  Maybe just go for it and collect some
feedback with a patch.

Cheers,
Remco

Re: Examples of local-host-entries or hosts-service-type?

[Gary Johnson]

2023/02/10 23:40, Sergiu Ivanov:

> I am reconfiguring my system right now, and guix system reconfigure
> /etc/config.scm tells me this:
>
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:126:27: warning: 'local-host-aliases' is deprecated, use 'local-host-entries' instead
> /etc/config.scm:124:14: warning: the 'hosts-file' field is deprecated, please use 'hosts-service-type' instead
>
> For the record, here are the lines guix system reconfigure is
> complaining about:
>
> (hosts-file (plain-file "hosts"
> 			(string-append
> 			 (local-host-aliases host-name)
> 			 "some.ip.address.1 machine1\n"
> 			 "some.other.ip.address machine2\n")))
>
> I spent quite some time trying to find some examples of using
> local-host-entries or hosts-service-type, but I don't seem to find any
> mention of these.  Quite on the contrary, the Guix manual actually seems
> to advice declarations similar to those which I have in my
> /etc/config.scm.
>
> Could someone point me to an example of how I should update
> my configuration?

Hi Sergiu et al,

  I just went through this exercise myself, and I decided to keep my
extra /etc/hosts entries in a separate text file using the original
hosts format. This makes them much easier for me to read and edit. To
provide them to the `hosts-service-type` service, I went ahead and wrote
a little importer function in Scheme that I thought some other folks
might benefit from. Here it is along with how to use it in your
`operating-system` declaration:

```scheme
(use-modules
 ((gnu services base)    #:select (hosts-service-type host))
 ((gnu services desktop) #:select (%desktop-services))
 ((gnu services)         #:select (simple-service))
 ((gnu system)           #:select (operating-system))
 ((ice-9 ports)          #:select (call-with-input-file))
 ((ice-9 textual-ports)  #:select (get-string-all)))

(define (load-hosts-entries)
  (call-with-input-file "etcfiles/extra-hosts"
    (lambda (p)
      (let* ((text   (get-string-all p))
             (lines  (string-split text #\newline))
             (lines* (filter (lambda (l) (not (or (string-null? l) (string-prefix? "#" l)))) lines)))
        (map (lambda (l)
               (let* ((tokens  (string-split l #\space))
                      (tokens* (filter (lambda (t) (not (string-null? t))) tokens))
                      (ip      (car tokens*))
                      (alias   (cadr tokens*)))
                 (host ip alias)))
             lines*)))))

(operating-system
  ...
  (services (cons* (simple-service 'add-extra-hosts hosts-service-type (load-hosts-entries))
                   ...
                   %desktop-services)))
```

To make this work, I have my additional hosts entries in a file called
"etcfiles/extra-hosts" relative to the location of my `system.scm` file
(which contains the `operating-system` declaration above).

That file looks like so:

```
# Section Comment 1
10.1.30.1 name1    # Maybe a comment for myself
10.1.30.2 name2
10.1.30.3 name3
10.1.30.4 name4    # Another comment

# Section Comment 2
10.6.1.1 name5
10.6.1.2 name6     # And yet another comment
10.6.1.3 name7
10.6.1.4 name8
```

This is, of course, the regular /etc/hosts format. I just leave out the
127.0.0.1 and ::1 entries for localhost since Guix adds those
automatically.

Also, please note that the Guix info pages are incorrect for
`hosts-service-type` and `host`. The docs say they are exported by `(gnu
services)`, but they are actually located in `(gnu services base)`. It
would be great if one of the manual maintainers could fix this mistake
as it was one of the trickiest things I had to figure out to make this
code work.

Thanks and happy hacking!
  Gary

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Re: Examples of local-host-entries or hosts-service-type?

[Sergiu Ivanov]

Hi Gary,

Gary Johnson <lambdatronic@disroot.org> [2023-02-21T16:33:25+0100]:
> 2023/02/10 23:40, Sergiu Ivanov:
>>
>> Could someone point me to an example of how I should update
>> my configuration?
>
>   I just went through this exercise myself, and I decided to keep my
> extra /etc/hosts entries in a separate text file using the original
> hosts format. This makes them much easier for me to read and edit. To
> provide them to the `hosts-service-type` service, I went ahead and wrote
> a little importer function in Scheme that I thought some other folks
> might benefit from.

Wow, thanks a lot for sharing!  You even handle comments :clap:

I admit that I literally have 2 entries to add to my /etc/hosts, so
I will still go with the manual addition as suggested by Bruno and
Remco, but I will keep your solution in mind!

> Also, please note that the Guix info pages are incorrect for
> `hosts-service-type` and `host`. The docs say they are exported by `(gnu
> services)`, but they are actually located in `(gnu services base)`.

Yeah, people seem to be actively working on this particular part of Guix
at the moment, including the docs.  I guess stuff will get fixed soon.

-
Sergiu

Re: Examples of local-host-entries or hosts-service-type?

[Bruno Victal]

Hi Remco,

On 2023-02-11 11:46, Remco van 't Veer wrote:
>        (hosts-service-type config =>
>                            (cons* (host "some.ip.address.1" "machine1")
>                                   (host "some.other.ip.address" "machine2")
>                                   (local-host-entries host-name)))))

This is not the "right" way to do use the service, the proper way is to extend this service
(as described in the manual) by:

--8<---------------cut here---------------start------------->8---
(simple-service 'add-extra-hosts
                hosts-service-type
                (list (host "192.0.2.1" "example.com"
                            '("example.net" "example.org"))
                      (host "2001:db8::1" "example.com"
                            '("example.net" "example.org"))))
--8<---------------cut here---------------end--------------->8---

You only override the hosts-service-type value when you don't want to have
'localhost' as an alias of your _hostname_ or you don't want to set '127.0.0.1' / '::1'
as IPs for localhost / _hostname_.

> local-host-entries

This procedure is for internal guix use, it isn't really meant to be used outside.
In fact, I think it shouldn't be exported at all since it's only use is to set the default value of
hosts-service-type.


Cheers,
Bruno

Re: Examples of local-host-entries or hosts-service-type?

[Sergiu Ivanov]

Hi Bruno and Remco,

Thank you for your messages and sorry for the delay with the answer.


Bruno Victal <mirai@makinata.eu> [2023-02-21T17:45:09+0100]:
> Hi Remco,
>
> On 2023-02-11 11:46, Remco van 't Veer wrote:
>>        (hosts-service-type config =>
>>                            (cons* (host "some.ip.address.1" "machine1")
>>                                   (host "some.other.ip.address" "machine2")
>>                                   (local-host-entries host-name)))))
>
> This is not the "right" way to do use the service, the proper way is to extend this service
> (as described in the manual) by:
>
> (simple-service 'add-extra-hosts
>                 hosts-service-type
>                 (list (host "192.0.2.1" "example.com"
>                             '("example.net" "example.org"))
>                       (host "2001:db8::1" "example.com"
>                             '("example.net" "example.org"))))

Thanks a lot!  I added this to my services in operating-system and it
worked flawlessly.

> You only override the hosts-service-type value when you don't want to have
> 'localhost' as an alias of your _hostname_ or you don't want to set '127.0.0.1' / '::1'
> as IPs for localhost / _hostname_.

Oh, good to know that!

>> local-host-entries
>
> This procedure is for internal guix use, it isn't really meant to be used outside.
> In fact, I think it shouldn't be exported at all since it's only use is to set the default value of
> hosts-service-type.

I have just done a guix pull and the new version of Guix does not
recognize local-host-entries any more. Apparently someone has removed
the export, as you suggested.

In terms of the docs, I don't find the entry for hosts-service-type here
any more:

https://guix.gnu.org/manual/en/manual/devel/en/html_node/Service-Reference.html

even though this is where I found the information about
hosts-service-type last week, and a cached version of the page still
shows this entry.

I guess Guix People are working on the subject at the moment, so I will
contain my zeal to update the documentation a little bit :D

-
Sergiu

Re: Examples of local-host-entries or hosts-service-type?

[Remco van 't Veer]

Hi Bruno,

Thanks for the clarification!

2023/02/21 16:45, Bruno Victal:

> You only override the hosts-service-type value when you don't want to
> have 'localhost' as an alias of your _hostname_ or you don't want to
> set '127.0.0.1' / '::1' as IPs for localhost / _hostname_.

Or when you want to provide extra aliases for localhost?

Like this?

  (essential-services
   (modify-services
       (operating-system-default-essential-services this-operating-system)
     (hosts-service-type config =>
                         (list (host "127.0.0.1" "localhost" (list host-name "foo" "bar"))
                               (host "::1"       "localhost" (list host-name "foo" "bar"))))))

Cheers,
Remco

Re: Examples of local-host-entries or hosts-service-type?

[Bruno Victal]

Hi Remco,

On 2023-02-27 06:23, Remco van 't Veer wrote:
> 
> Or when you want to provide extra aliases for localhost?
> 
> Like this?
> 
>   (essential-services
>    (modify-services
>        (operating-system-default-essential-services this-operating-system)
>      (hosts-service-type config =>
>                          (list (host "127.0.0.1" "localhost" (list host-name "foo" "bar"))
>                                (host "::1"       "localhost" (list host-name "foo" "bar"))))))

Semantically you're right though I wouldn't outright do this unless it results in clearer code or if its really needed.

Reason for this is that the format of /etc/hosts isn't consistently defined.
For instance, there is a limit on the maximum number of aliases. (depending on the implementation)

If I wanted to add extra aliases, I'd extend the service with new "standalone" host records instead though your snippet
is just as valid, as long you don't go overboard with the number of aliases.


Cheers,
Bruno

Re: Examples of local-host-entries or hosts-service-type?

[Remco van 't Veer]

Hi Bruno,

2023/03/02 02:41, Bruno Victal:

> On 2023-02-27 06:23, Remco van 't Veer wrote:
>>
>> Or when you want to provide extra aliases for localhost?
>>
>> Like this?
>>
>>   (essential-services
>>    (modify-services
>>        (operating-system-default-essential-services this-operating-system)
>>      (hosts-service-type config =>
>>                          (list (host "127.0.0.1" "localhost" (list host-name "foo" "bar"))
>>                                (host "::1"       "localhost" (list host-name "foo" "bar"))))))
>
> Semantically you're right though I wouldn't outright do this unless it
> results in clearer code or if its really needed.
>
> Reason for this is that the format of /etc/hosts isn't consistently
> defined.
> For instance, there is a limit on the maximum number of
> aliases. (depending on the implementation)
>
> If I wanted to add extra aliases, I'd extend the service with new
> "standalone" host records instead though your snippet is just as
> valid, as long you don't go overboard with the number of aliases.

I not sure all applications will react well to having multiple entries
for the same IP-address.

From the hosts(5) manpage:

> This file is a simple text file that associates IP addresses with
> hostnames, one line per IP address.

To workaround the alias limit, picking multiple loopback addresses (for
the example above) would be a better solution, it seems.

Cheers,
Remco

Re: Examples of local-host-entries or hosts-service-type?

[Bruno Victal]

On 2023-03-02 08:47, Remco van 't Veer wrote:
> I not sure all applications will react well to having multiple entries
> for the same IP-address.

[...]

> 
> From the hosts(5) manpage:
> 
>> This file is a simple text file that associates IP addresses with
>> hostnames, one line per IP address.

It doesn't state that the IP addresses must be unique.

Were that the case then blacklists such as <https://someonewhocares.org/hosts/hosts>
which employ the hosts file method would be broken.
AFAIK this method has around for a long time, I don't see this behavior changing anytime soon
even if it turned out to be "against spec".

Cheers,
Bruno

Re: Examples of local-host-entries or hosts-service-type?

[Remco van 't Veer]

Bruno Victal wrote:

>Were that the case then blacklists such as <https://someonewhocares.org/hosts/hosts>
>which employ the hosts file method would be broken.
>AFAIK this method has around for a long time, I don't see this behavior changing anytime soon
>even if it turned out to be "against spec".

Makes sense. Thanks.

Cheers,
Remco