agetty and special chars @ and #

agetty and special chars @ and #

[Karel Zak]

 Hi Werner,

 agetty in get_logname() interprets '@' and '#' as a special chars
 (see man page or the code for more details).

 The problem is that we already have crazy users who want to use AD
 (access domain) usernames in format user@domain on serial line or
 console.

 Yeah, I know that char '@' is not between allowed username chars
 (POSIX 3.429), but do we really need to support the spacial
 interpretation of the @ and # chars?

 I think it's old confusing legacy. Objections?

    Karel


-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: agetty and special chars @ and #

[Dr. Werner Fink]

On Wed, Nov 07, 2012 at 05:58:59PM +0100, Karel Zak wrote:
> 
>  Hi Werner,
> 
>  agetty in get_logname() interprets '@' and '#' as a special chars
>  (see man page or the code for more details).
> 
>  The problem is that we already have crazy users who want to use AD
>  (access domain) usernames in format user@domain on serial line or
>  console.
> 
>  Yeah, I know that char '@' is not between allowed username chars
>  (POSIX 3.429), but do we really need to support the spacial
>  interpretation of the @ and # chars?
> 
>  I think it's old confusing legacy. Objections?

Hmmm ... AFAICR the '@' symbols can be used to set the kill character
and the '#' can be used to set the erase character.  But for a virtual
console terminal those characters those are normally not used.

Only connections at dialin as well connections over some serial lines
with hardware/software line routers/terminal servers between this could
be problem.  On big irons such serial lines are used even in the present
days.

Maybe it would be worth to introduce an further option to support
access domains in user names ... or the other way around to support
'@' and '#' as special characters used for software escapes on
oldish connection lines.


   Werner

http://www.linusakesson.net/programming/tty/
http://digilander.libero.it/robang/rubrica/serial.htm

-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr

Re: agetty and special chars @ and #

[Karel Zak]

On Mon, Nov 12, 2012 at 11:04:11AM +0100, Dr. Werner Fink wrote:
> On Wed, Nov 07, 2012 at 05:58:59PM +0100, Karel Zak wrote:
> > 
> >  Hi Werner,
> > 
> >  agetty in get_logname() interprets '@' and '#' as a special chars
> >  (see man page or the code for more details).
> > 
> >  The problem is that we already have crazy users who want to use AD
> >  (access domain) usernames in format user@domain on serial line or
> >  console.
> > 
> >  Yeah, I know that char '@' is not between allowed username chars
> >  (POSIX 3.429), but do we really need to support the spacial
> >  interpretation of the @ and # chars?
> > 
> >  I think it's old confusing legacy. Objections?
> 
> Hmmm ... AFAICR the '@' symbols can be used to set the kill character
> and the '#' can be used to set the erase character.  But for a virtual
> console terminal those characters those are normally not used.
> 
> Only connections at dialin as well connections over some serial lines
> with hardware/software line routers/terminal servers between this could
> be problem.  On big irons such serial lines are used even in the present
> days.
> 
> Maybe it would be worth to introduce an further option to support
> access domains in user names ... or the other way around to support
> '@' and '#' as special characters used for software escapes on
> oldish connection lines.

 I thought about something like:

    --erase-chars <string>
    --kill-chars  <string>

 and if the string is empty then agetty is insensitive to the special
 chars. This should be a default for virtual console (or also for
 serial line?).

 vice versa

   agetty --erase-chars '#'

 enables the support for the char.

 IMHO this solution is easy to extend (you can use another chars) and
 provides full control of the feature (you can disable it at all).

    Karel

> 
> 
>    Werner
> 
> http://www.linusakesson.net/programming/tty/
> http://digilander.libero.it/robang/rubrica/serial.htm
> 
> -- 
>   "Having a smoking section in a restaurant is like having
>           a peeing section in a swimming pool." -- Edward Burr
> --
> To unsubscribe from this list: send the line "unsubscribe util-linux" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: agetty and special chars @ and #

[Dr. Werner Fink]

On Mon, Nov 12, 2012 at 02:29:26PM +0100, Karel Zak wrote:
> On Mon, Nov 12, 2012 at 11:04:11AM +0100, Dr. Werner Fink wrote:
> > On Wed, Nov 07, 2012 at 05:58:59PM +0100, Karel Zak wrote:
> > > 
> > >  Hi Werner,
> > > 
> > >  agetty in get_logname() interprets '@' and '#' as a special chars
> > >  (see man page or the code for more details).
> > > 
> > >  The problem is that we already have crazy users who want to use AD
> > >  (access domain) usernames in format user@domain on serial line or
> > >  console.
> > > 
> > >  Yeah, I know that char '@' is not between allowed username chars
> > >  (POSIX 3.429), but do we really need to support the spacial
> > >  interpretation of the @ and # chars?
> > > 
> > >  I think it's old confusing legacy. Objections?
> > 
> > Hmmm ... AFAICR the '@' symbols can be used to set the kill character
> > and the '#' can be used to set the erase character.  But for a virtual
> > console terminal those characters those are normally not used.
> > 
> > Only connections at dialin as well connections over some serial lines
> > with hardware/software line routers/terminal servers between this could
> > be problem.  On big irons such serial lines are used even in the present
> > days.
> > 
> > Maybe it would be worth to introduce an further option to support
> > access domains in user names ... or the other way around to support
> > '@' and '#' as special characters used for software escapes on
> > oldish connection lines.
> 
>  I thought about something like:
> 
>     --erase-chars <string>
>     --kill-chars  <string>
> 
>  and if the string is empty then agetty is insensitive to the special
>  chars. This should be a default for virtual console (or also for
>  serial line?).
> 
>  vice versa
> 
>    agetty --erase-chars '#'
> 
>  enables the support for the char.
> 
>  IMHO this solution is easy to extend (you can use another chars) and
>  provides full control of the feature (you can disable it at all).

Indeed this is a good solution ... but in the case of systemd and its
getty generator we may think about a /etc/agettytab with a similar
syntax scheme as the old /etc/inittab to be able to provide agetty
options based on the used tty line.  Clearly this /etc/agettytab should
be parsed by agetty and options for the specified tty are found:

  1:tty1:--noclear %p
  2:tty2:%p
  3:tty3:%p
  4:tty4:%p
  5:tty5:%p
  6:tty6:%p
  S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
  S1:ttyS0:-L 9600 %p 9600 vt102

... ??

    Werner

-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr

Re: agetty and special chars @ and #

[Karel Zak]

On Wed, Nov 14, 2012 at 03:27:20PM +0100, Dr. Werner Fink wrote:
> Indeed this is a good solution ... but in the case of systemd and its
> getty generator we may think about a /etc/agettytab with a similar
> syntax scheme as the old /etc/inittab to be able to provide agetty
> options based on the used tty line.  Clearly this /etc/agettytab should
> be parsed by agetty and options for the specified tty are found:
> 
>   1:tty1:--noclear %p
>   2:tty2:%p
>   3:tty3:%p
>   4:tty4:%p
>   5:tty5:%p
>   6:tty6:%p
>   S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
>   S1:ttyS0:-L 9600 %p 9600 vt102

 Hmm, I guess it's still possible to create tty line specific config
 file on systems with systemd. I'd like to avoid another place where
 will be configuration.

 Lennart?



-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: agetty and special chars @ and #

[Lennart Poettering]

On Fri, 16.11.12 11:14, Karel Zak (kzak@redhat.com) wrote:

> 
> On Wed, Nov 14, 2012 at 03:27:20PM +0100, Dr. Werner Fink wrote:
> > Indeed this is a good solution ... but in the case of systemd and its
> > getty generator we may think about a /etc/agettytab with a similar
> > syntax scheme as the old /etc/inittab to be able to provide agetty
> > options based on the used tty line.  Clearly this /etc/agettytab should
> > be parsed by agetty and options for the specified tty are found:
> > 
> >   1:tty1:--noclear %p
> >   2:tty2:%p
> >   3:tty3:%p
> >   4:tty4:%p
> >   5:tty5:%p
> >   6:tty6:%p
> >   S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
> >   S1:ttyS0:-L 9600 %p 9600 vt102
> 
>  Hmm, I guess it's still possible to create tty line specific config
>  file on systems with systemd. I'd like to avoid another place where
>  will be configuration.

Please do not add such a configuration file.

In systemd, if people want to configure line-specific getty
configuration they should just copy
/usr/lib/systemd/system/getty@.service to
/etc/systemd/system/getty@ttyS0.service and edit it there. Since systemd
will first look for instantiated unit files, and only then fall back to
generic template this should do the right thing.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.

Re: agetty and special chars @ and #

[Karel Zak]

On Fri, Nov 16, 2012 at 01:47:29PM +0100, Lennart Poettering wrote:
> On Fri, 16.11.12 11:14, Karel Zak (kzak@redhat.com) wrote:
> 
> > 
> > On Wed, Nov 14, 2012 at 03:27:20PM +0100, Dr. Werner Fink wrote:
> > > Indeed this is a good solution ... but in the case of systemd and its
> > > getty generator we may think about a /etc/agettytab with a similar
> > > syntax scheme as the old /etc/inittab to be able to provide agetty
> > > options based on the used tty line.  Clearly this /etc/agettytab should
> > > be parsed by agetty and options for the specified tty are found:
> > > 
> > >   1:tty1:--noclear %p
> > >   2:tty2:%p
> > >   3:tty3:%p
> > >   4:tty4:%p
> > >   5:tty5:%p
> > >   6:tty6:%p
> > >   S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
> > >   S1:ttyS0:-L 9600 %p 9600 vt102
> > 
> >  Hmm, I guess it's still possible to create tty line specific config
> >  file on systems with systemd. I'd like to avoid another place where
> >  will be configuration.
> 
> Please do not add such a configuration file.
> 
> In systemd, if people want to configure line-specific getty
> configuration they should just copy
> /usr/lib/systemd/system/getty@.service to
> /etc/systemd/system/getty@ttyS0.service and edit it there. Since systemd
> will first look for instantiated unit files, and only then fall back to
> generic template this should do the right thing.

It would be nice to make it more obvious in systemd.special man page.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: agetty and special chars @ and #

[Lennart Poettering]

On Fri, 16.11.12 14:05, Karel Zak (kzak@redhat.com) wrote:

> 
> On Fri, Nov 16, 2012 at 01:47:29PM +0100, Lennart Poettering wrote:
> > On Fri, 16.11.12 11:14, Karel Zak (kzak@redhat.com) wrote:
> > 
> > > 
> > > On Wed, Nov 14, 2012 at 03:27:20PM +0100, Dr. Werner Fink wrote:
> > > > Indeed this is a good solution ... but in the case of systemd and its
> > > > getty generator we may think about a /etc/agettytab with a similar
> > > > syntax scheme as the old /etc/inittab to be able to provide agetty
> > > > options based on the used tty line.  Clearly this /etc/agettytab should
> > > > be parsed by agetty and options for the specified tty are found:
> > > > 
> > > >   1:tty1:--noclear %p
> > > >   2:tty2:%p
> > > >   3:tty3:%p
> > > >   4:tty4:%p
> > > >   5:tty5:%p
> > > >   6:tty6:%p
> > > >   S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
> > > >   S1:ttyS0:-L 9600 %p 9600 vt102
> > > 
> > >  Hmm, I guess it's still possible to create tty line specific config
> > >  file on systems with systemd. I'd like to avoid another place where
> > >  will be configuration.
> > 
> > Please do not add such a configuration file.
> > 
> > In systemd, if people want to configure line-specific getty
> > configuration they should just copy
> > /usr/lib/systemd/system/getty@.service to
> > /etc/systemd/system/getty@ttyS0.service and edit it there. Since systemd
> > will first look for instantiated unit files, and only then fall back to
> > generic template this should do the right thing.
> 
> It would be nice to make it more obvious in systemd.special man page.

But the getty is actually not thaaaat special, it's actually just a unit
like any other with no special semantics.

This general approach is actually well documented, for example most
recently here:

http://0pointer.de/blog/projects/serial-console.html

Indirectly this all is also listed in the FAQ:

http://www.freedesktop.org/wiki/Software/systemd/FrequentlyAskedQuestions

Lennart

-- 
Lennart Poettering - Red Hat, Inc.

Re: [util-linux] agetty and special chars @ and #

[Dr. Werner Fink]

On Tue, Nov 20, 2012 at 01:47:23AM +0100, Lennart Poettering wrote:
> On Fri, 16.11.12 14:05, Karel Zak (kzak@redhat.com) wrote:
> 
> > 
> > On Fri, Nov 16, 2012 at 01:47:29PM +0100, Lennart Poettering wrote:
> > > On Fri, 16.11.12 11:14, Karel Zak (kzak@redhat.com) wrote:
> > > 
> > > > 
> > > > On Wed, Nov 14, 2012 at 03:27:20PM +0100, Dr. Werner Fink wrote:
> > > > > Indeed this is a good solution ... but in the case of systemd and its
> > > > > getty generator we may think about a /etc/agettytab with a similar
> > > > > syntax scheme as the old /etc/inittab to be able to provide agetty
> > > > > options based on the used tty line.  Clearly this /etc/agettytab should
> > > > > be parsed by agetty and options for the specified tty are found:
> > > > > 
> > > > >   1:tty1:--noclear %p
> > > > >   2:tty2:%p
> > > > >   3:tty3:%p
> > > > >   4:tty4:%p
> > > > >   5:tty5:%p
> > > > >   6:tty6:%p
> > > > >   S0:ttyS0:--erase-chars # --kill-chars @ -mt 60 %p 9600,2400,1200
> > > > >   S1:ttyS0:-L 9600 %p 9600 vt102
> > > > 
> > > >  Hmm, I guess it's still possible to create tty line specific config
> > > >  file on systems with systemd. I'd like to avoid another place where
> > > >  will be configuration.
> > > 
> > > Please do not add such a configuration file.
> > > 
> > > In systemd, if people want to configure line-specific getty
> > > configuration they should just copy
> > > /usr/lib/systemd/system/getty@.service to
> > > /etc/systemd/system/getty@ttyS0.service and edit it there. Since systemd
> > > will first look for instantiated unit files, and only then fall back to
> > > generic template this should do the right thing.
> > 
> > It would be nice to make it more obvious in systemd.special man page.
> 
> But the getty is actually not thaaaat special, it's actually just a unit
> like any other with no special semantics.
> 
> This general approach is actually well documented, for example most
> recently here:
> 
> http://0pointer.de/blog/projects/serial-console.html
> 
> Indirectly this all is also listed in the FAQ:
> 
> http://www.freedesktop.org/wiki/Software/systemd/FrequentlyAskedQuestions

Hi Lennart,

you and also I know how to do this, nevertheless just one remark: for most
other users this is black magic (and most users are aliterate at the first
moment).  This because they are not aware how the systemd-getty-generator
nor how the getty services have to be read.  It is not at first glance
obviously from getty@.service nor serial-getty@.service how to get an other
getty for a special serial console nor how to have a getty with a special
option for e.g. for tty1.

The complexity level is to high due to the fact that there are to many
locations and set screws to influence the numbers, devices, and options
of the gettys.

If you like to avoid such simply approaches for agetty you may consider to
help normal users which do not work daily as system administrators to help
them by providing all infomations in a more comprehensible and user friendly
form in *one* file.  That could be that the getty-generator my use informations
from getty@.service and serial-getty@.service them self.

In other words: usability by striking simplicity :)

   Werner

-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr

Re: [util-linux] agetty and special chars @ and #

[Lennart Poettering]

On Tue, 20.11.12 10:26, Dr. Werner Fink (werner@suse.de) wrote:

> > But the getty is actually not thaaaat special, it's actually just a unit
> > like any other with no special semantics.
> > 
> > This general approach is actually well documented, for example most
> > recently here:
> > 
> > http://0pointer.de/blog/projects/serial-console.html
> > 
> > Indirectly this all is also listed in the FAQ:
> > 
> > http://www.freedesktop.org/wiki/Software/systemd/FrequentlyAskedQuestions
> 
> Hi Lennart,
> 
> you and also I know how to do this, nevertheless just one remark: for most
> other users this is black magic (and most users are aliterate at the first
> moment).  This because they are not aware how the systemd-getty-generator
> nor how the getty services have to be read.  It is not at first glance
> obviously from getty@.service nor serial-getty@.service how to get an other
> getty for a special serial console nor how to have a getty with a special
> option for e.g. for tty1.
>
> The complexity level is to high due to the fact that there are to many
> locations and set screws to influence the numbers, devices, and options
> of the gettys.

Well, I am not really sure I buy into the complexity thing so much. We
use the same concepts for making changes to any service here, really. So
if an admin grokked this once he should be able to apply this to any
service he likes.

> If you like to avoid such simply approaches for agetty you may consider to
> help normal users which do not work daily as system administrators to help
> them by providing all infomations in a more comprehensible and user friendly
> form in *one* file.  That could be that the getty-generator my use informations
> from getty@.service and serial-getty@.service them self.
> 
> In other words: usability by striking simplicity :)

I really don't agree that adding multiple levels of configuration really
would be such a good idea. Adding redundancy by implementing several
different ways to configure the same thing just adds confusion and
complexity in my eyes.

Note that systemd-getty-generator actually comes with a man page. Of
course, it's a problem to get people to actually find it, or even know
about it.

I have now updated the Documentation= field of the getty services to
point to the aforementioned blog story (this will then show up in
systemctl status), and added similar links to all man pages in any way
related to getty configuration. I think this is the best we can do:
keeping things uniform and not redundant, while beefing up docs and
making them easier to find.

Hope this settles this,

Lennart

-- 
Lennart Poettering - Red Hat, Inc.