On Wed, 24 Dec 2008, Erik Mouw wrote:
> On Tue, 23 Dec 2008 17:56:00 -0500 (EST) "Robert P. J. Day"
> <rpjday@xxxxxxxxxxxxxx> wrote:
> > i'm well aware of the use of the pseudo tty ports under
> > /dev/pts, but i never understood the value of having a distinct
> > "devpts" filesystem, until today.
> >
> > i was working with an embedded system with a flashed root
> > filesystem that included /dev so, obviously, everything under /dev
> > was also read only. i installed dropbear for an ssh server, but
> > every attempt to ssh to that system failed.
>
> Ssh (or actually any login kind of program) wants to chown/chmod the
> controlling tty, which is of course not possible on a RO filesystem.
yes, i found that out the hard way.
> > after tracing the operation of dropbear, i tracked it down to
> > the fact that dropbear was trying to open a pseudo-port
> > corresponding to the connection and was, of course, failing since
> > all of /dev was read-only.
> >
> > after i mounted /dev/pts (rw), ssh connections started to work.
> > is this why /dev/pts was developed? to work around RO /dev
> > directories? or was there some other reason?
>
> No, that's just coincidence. The main reason is that in the old days
> the number of PTYs were limited (to 256, IIRC) so you could only
> have a limited number of remote sessions and xterms on your machine.
> /dev/pts removed that limit.
i've never been in the situation of running out of ptys but are you
saying that if i don't mount devpts and use /dev/pts as a regular
directory, i will hit a hard limit of 256 special files that i
wouldn't hit using the mount?
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
Have classroom, will lecture.
http://crashcourse.ca Waterloo, Ontario, CANADA
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