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Vieri
l33t
Joined: 18 Dec 2005
Posts: 877
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 Posted: Fri Apr 25, 2014 12:11 pm Post subject: [SOLVED] redirect output to a console (tty) |
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Hi,
I'm trying to boot with a custom script displaying messages in tty3 which in turn launches another custom script which should display its own messages in tty2.
Somehow it's not working as expected.
My custom test scripts are:
| Code: |
# cat /opt/test/console3.sh
#/bin/sh
stty sane < /dev/tty3
stty sane < /dev/tty2
printf "%s" "tty3: in loop" >& /dev/tty3 < /dev/tty3
/opt/test/console2.sh >& /dev/tty2 < /dev/tty2
while [ 1 ];
do
printf "%s" "." & >/dev/tty3 < /dev/tty3
sleep 5
done
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| Code: |
# cat /opt/test/console2.sh
#/bin/sh
printf "%s" "tty2: in loop"
while [ 1 ];
do
printf "%s" "."
sleep 5
done
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From inittab I'm launching console3.sh and I'm not launching anything in tty2:
| Code: |
# grep "^c" /etc/inittab
c1:12345:respawn:/sbin/agetty 38400 tty1 linux
c3:3:respawn:/opt/test/console3.sh
c4:2345:respawn:/sbin/agetty 38400 tty4 linux
c5:2345:respawn:/sbin/agetty 38400 tty5 linux
c6:2345:respawn:/sbin/agetty 38400 tty6 linux
ca:12345:ctrlaltdel:/sbin/shutdown -r now
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When I boot the system for the first time and I press ALT-F2 I can see the correct messages displayed by console2.sh in tty2, ie. I can read "tty2: in loop....." (and the dots keep coming up every 5 seconds).
However, if I press ALT-F3 I can see the message "tty3: in loop" but nothing afterwards, ever (no dots). It's as if launching console2.sh from console3.sh was blocking the rest of the execution.
So how can I correctly fork another script (and keep going) so it redirects its output to another tty?
As a side note, I can't seem to list the "console2.sh" process.
| Code: |
# ps aux | grep console
root 17987 0.0 0.0 3564 1300 ? Ss 12:36 0:00 /bin/sh /opt/test/console3.sh
root 17994 0.0 0.0 3564 816 ? S 12:36 0:00 /bin/sh /opt/test/console3.sh
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Why doesn't "console2.sh" appear in the listing?
After killing 17987 and doing "ps axjf" I can see the following:
| Code: |
1 17994 17987 17987 ? -1 S 0 0:00 /bin/sh /opt/test/console3.sh
17994 19290 17987 17987 ? -1 S 0 0:00 \_ sleep 5
1 19008 19008 19008 ? -1 Ss 0 0:00 /bin/sh /opt/test/console3.sh
19008 19011 19008 19008 ? -1 S 0 0:00 \_ /bin/sh /opt/test/console3.sh
19011 19291 19008 19008 ? -1 S 0 0:00 \_ sleep 5
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Thanks
Vieri
Last edited by Vieri on Mon Apr 28, 2014 5:50 pm; edited 1 time in total |
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mv
Watchman
Joined: 20 Apr 2005
Posts: 6747
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| Posted: Fri Apr 25, 2014 1:55 pm Post subject: |
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I strongly suggest you to avoid this stupid >& bashism: Use the compatible >... 2>&1 instead and your problems wlil disappear:
| Quote: | | Code: | | printf "%s" "." & >/dev/tty3 < /dev/tty3 |
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This line means: run printf in the background, and redirect stdoout/stdin to/from /dev/tty3 for the empty command.
Another issue might be that stdout might be buffered |
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Vieri
l33t
Joined: 18 Dec 2005
Posts: 877
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| Posted: Mon Apr 28, 2014 7:47 am Post subject: |
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Thanks for the tip.
So I changed console3.sh to:
| Code: |
# cat /opt/test/console3.sh
#/bin/sh
stty sane < /dev/tty3
stty sane < /dev/tty2
printf "%s" "tty3: in loop" >/dev/tty3 < /dev/tty3
/opt/test/console2.sh & >/dev/tty2 < /dev/tty2
while [ 1 ];
do
printf "%s" "." >/dev/tty3 < /dev/tty3
sleep 5
done
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It seems to work fine except for the fact that the output of console2.sh is not in tty2 but in tty1. I'd like to call a script in the background and tell it to to redirect it's output to a specific tty, without needing to touch that script's source code (console2.sh).
Also, I'm still not seeing 'console2.sh' if I do 'ps aux'. I just see 2 console3.sh processes. |
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mv
Watchman
Joined: 20 Apr 2005
Posts: 6747
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| Posted: Mon Apr 28, 2014 4:03 pm Post subject: |
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| Vieri wrote: | | I'd like to call a script in the background and tell it to to redirect it's output to a specific tty |
Oh, and I thought your "& >" was a typo for the bashism "&>". Now I see that you really intended printf to be a background task.
In this case order matters: runs "echo 1 with redirection to foo" in background. In contrast, runs "echo 1" in background and then redirects the output of the empty command to foo,
(To memorize this, you should think of "&" as a separator like ";" or like a newline character.)
In other words: Putting & in your above code to the end of the line should do what you want. |
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Vieri
l33t
Joined: 18 Dec 2005
Posts: 877
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| Posted: Mon Apr 28, 2014 5:49 pm Post subject: |
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| I must be blind or in need of a vacation... Simple enough. Thanks for the explanation! |
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