[NBLUG/talk] Re: xminicom problems

ME dugan at passwall.com
Tue Jul 1 05:11:01 PDT 2003


Jim Bianchi said:
> On Mon, 30 Jun 2003 talk-request at nblug.org wrote:
>>Yes. Often, you will find devices owned by a specific user and group.
>
> [root at garbanzo /dev]# ls -l ttyS4
> crwxrwx--x   1  root    uucp    <yacketa-yacketa>
>
>
> 	After searching through /etc/group/ and finding nothing at all
> that looked as if it might help, I returned to /dev/ttyS4, and chmoded
> it:
>
> [root at garbanzo /dev]# ls -l ttyS4
> crwxrwxrwx   1  root    uucp    <yacketa-yacketa>

The group in this case would have been "uucp". That group should exist in
your /etc/group file. However, are your other serial "dev" owned by this
same group?

(BTW, uucp is "Unix to Unix Copy" - a network-based copy protocol (like
ftp, telnet and hhtp are network-based protocols) frequently used many
ages ago to copy files between unix systems-- sort of like a very early
rsync, but not so advanced.)

The better solution would have been to just add yourself to the "uucp"
group or duplicated ownership of the other serial ports and added yourself
to that group. By setting this device with permissions like these, any
user on your system can now use your modem to dial out.

If you just added yourself to the group and/or used a separate group, you
could control who used the modem by who was in that group. (Add/remove
people as needed.) By using such a group system, people could use the
modem from anywhere, and any tty only if they were in the group that owned
the device.

If you are the only user of the system, it is not so bad to have chmod 777
your device, but it is not what I would have done.

You should also make sure you have a symlink:

# ls -l /dev/modem
it should point to "ttyS4". If you dont have one, then make one:
# cd /dev
# ln -s ttyS4 modem

> 	And now it works. Part of the problem was my fault. I assumed
> that, hey, if you could execute a modem program, that should be all that
> was needed to be able to use the thing, right? Wrong. Unless you can
> figure a way to use a modem control program without ever reading from or
> writing to the file the pgm must talk to (/dev/ttyS4 in this case). Duhh.

This is a common thing that comes up. The worst thing to do (IMO) is make
the application SetUID root. Sun does that with many of their things and I
have a theory about why and how that leads to security problems for their
OS.

> 	FWIW, I'm using a Xircom RealPort Cardbus combo Ethernet 10/100
> and 56k modem PCMCIA card on a Dell Latitude C600. The laptop mobo has a
> built in 56k winmodem, but that is not even recognised by Linux (and from
> what I've read on the web, there is no chance it will ever be), so that's
> a total loss. But the Xircom PCMCIA modem seems to work well (esp once you
> get the permissions straight <grin>), and is to be recommended. It seems
> to respond to most all of the Hayes instruction set -- I plugged 'S11=40'
> into my modem init string to make it dial faster. Instead of a very slow
> 'beep' (pause) 'beep' (pause) 'boop' ... I get a rapid 'beedleebeepboop'
> that is emotionally satisfying. (I'm easily amused..)

Yep, I like fast dial too. a time of "20" was usually good in most places
I used it. Less than that and it did not work sometimes.

> 	I've not really done much with the eth0 thingy yet. But dmesg does
> indicate it is recognised, so at least Linux knows it's there. I'm still
> trying to get my DVD reader (xine) to stop pausing slightly the audio and
> video. Any suggestions on that one?

Just guessing for this. One of three common problems. (There are other
problems, but these are common.)
1) Your hardware (media or drive) has problems reading the disk due to bad
drive or scratch on media or errors on the disk
2) You CPU / Bus are too slow. Try resizing the displayed movie to a very
small resolution and see if there are fewer pauses.
3) As partly a result of #2 and/or other apps running, or issues with
needing multiple reads from a problem in #1, or ???, see if you can
increase the buffer/cache size for xine. (I know mplayer can do this.) By
setting the dvd player to have a large cache, it will pre-buffer  a lot of
the video (I precache 65M (and then occasional hiccups on the system dont
cause so many problems, as the app can "catchup" before I see the drop in
available data.

I have only used this with playback of files, not DVD, so others may have
other suggestions.

-ME





More information about the talk mailing list