/dev/tty problem and solution

[bzhou]

I flashed the modified 3.1.28 firmware with utelnetd and dropbear, and am trying out the optware packages, most things work fine. But there is one annoying problem, with symptoms of:

1. After login, Busybox shows

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can't access tty: job control turned off

2. /bin/more, /opt/bin/less, or any program that reads /dev/tty does not get any key press input
3. /opt/bin/ssh-keygen does not work, stops when reading /dev/tty
4. /opt/bin/ssh does not work, stops when reading /dev/tty

It turns out /dev/tty was symlinked to /dev/ttyS0.

So do the following

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# cd /dev
# rm -f tty
# mknod tty c 5 0
# chmod go+w tty


And everything's back to normal.

-Brian Zhou

[stuart_f]

Brian,

Great work. I wonder if the symlink was so that development boards (which presumably have the serial headers attached) could interact with the final firmware via the serial port. I can't think why else this has been done.

Not being able to read things with more was a bugbear before but works perfectly now.

[bzhou]

Unfortunately the problem appears again after reboot regardless of kernel. It's really set in /etc/udev/rules.d/50-udev.rules

To fix permanently, follow the instruction on http://www.nslu2-linux.org/wiki/MSSII/HomePage 2nd tip, copied here

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# cp /etc/udev/rules.d/50-udev.rules /etc/udev/rules.d/50-udev.rules.orig
# sed -i -e '/ttyS0.*SYMLINK="tty"/d; /console.*MODE="0622"/aKERNEL=="tty",     NAME="%k", MODE="0666"' /etc/udev/rules.d/50-udev.rules


Basically it does the following change with /bin/sed

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--- 50-udev.rules.orig  2007-10-13 02:35:50.000000000 +0000
+++ 50-udev.rules       2007-10-13 02:38:10.000000000 +0000
@@ -52,13 +52,13 @@
KERNEL="socksys",      SYMLINK="nfsd"
KERNEL="mtd0",         SYMLINK="mtd"
KERNEL="ttyS0",                SYMLINK="console"
-KERNEL="ttyS0",                SYMLINK="tty"
KERNEL="null",         SYMLINK="XOR"

# set some udev overwritten device permissions
KERNEL=="zero",    NAME="%k", MODE="0666"
KERNEL=="null",    NAME="%k", MODE="0666"
KERNEL=="console", NAME="%k", MODE="0622"
+KERNEL=="tty",     NAME="%k", MODE="0666"
KERNEL=="random",  NAME="%k", MODE="0444"
KERNEL=="urandom", NAME="%k", MODE="0444"


I've tested it to work, without affecting serial console.