redirect QEMU window output to terminal running qemu

Question

Im trying to debug the boot sequence of a linux kernel with qemu, the command i'm running is:

  qemu -serial stdio -kernel <path to kernel> -hda <path to rootfs> -append "root=/dev/sda terminal = ttyS0"

During boot all the kernel messages are printed to the QEMU window. Only when the boot has finished i get my prompt back to the terminal i ran QEMU in.

Now i can start using the kernel terminal I'm running and seeing the output in the terminal and not in QEMU window.

How do i get all messages including the boot messages to my terminal and not to QEMU window (because i cant scroll up in that window..) ?

http://stackoverflow.com/questions/18098455/redirect-qemu-console-to-a-file-or-the-host-terminal/18100781#18100781 — vinay hunachyal, Oct 24 '13 at 17:21
Possible duplicate of [How to use qemu to run a non-gui OS on the terminal?](https://stackoverflow.com/questions/6710555/how-to-use-qemu-to-run-a-non-gui-os-on-the-terminal) — Ciro Santilli OurBigBook.com, May 23 '18 at 04:06

score 48 · Accepted Answer · edited Oct 14 '16 at 09:55

48

remove -serial stdio parameter
add -nographic parameter
and change the kernel parameter terminal = ttyS0 to console=ttyS0. This should do the trick.

qemu -nographic -kernel ./bzImage -hda ./image.hda -append root=/dev/sda console=ttyS0

You may want to check the script I use for kernel development: https://github.com/arapov/wrap-qemukvm (it's not very "production", but you can find useful qemu cli parameters there)

edited Oct 14 '16 at 09:55

user123456

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answered Oct 24 '13 at 14:53

Anton

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Some emulated machines will need `console=ttyAMA0,115200` rather than `console=ttyS0`. Or you can just provide both as in vinay's answer. – simonp Nov 29 '14 at 08:19
Just check whether you want to set root=/dev/sda1 or /dev/sda . I had to set it to /dev/sda1 – Parag Gupta Feb 24 '16 at 11:59
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BTW, I've created a Buildroot version of your script: https://github.com/cirosantilli/linux-kernel-module-cheat – Ciro Santilli OurBigBook.com May 24 '17 at 06:24
After doing so, you might also want to automatically resize the serial console: https://unix.stackexchange.com/a/283206/92541 – VasiliNovikov Jan 28 '19 at 10:51

score 11 · Answer 2 · edited May 23 '17 at 12:17

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refer this Redirect Qemu console to a file or the host terminal? to get the log on both qemu and your terminal .use "console=ttyAMA0,115200 console=tty highres=off console=ttyS0"

edited May 23 '17 at 12:17

Community

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answered Oct 24 '13 at 17:26

vinay hunachyal

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It is not the solution for my trivial problem, the second tty console disappeared in qemu: http://raspberrypi.stackexchange.com/questions/56302/qemu-2-7-0-for-the-raspi2-machine-do-not-show-the-second-tty-console-only-the – 42n4 Oct 13 '16 at 16:27
@42n4 https://learningfromyoublog.wordpress.com/ or https://learningfromyoublog.wordpress.com/2016/04/05/131/ – vinay hunachyal Oct 14 '16 at 05:18
I used the qemu machine raspi2 and cpu arm1176 and compiled with armv7a-hardfloat the original raspberry kernel sources with bcm2709_defconfig, so all was very "native" and it is vary sad it is not working at once, look at my question makefile: http://raspberrypi.stackexchange.com/questions/56302/qemu-2-7-0-for-the-raspi2-machine-do-not-show-the-second-tty-console-only-the – 42n4 Oct 14 '16 at 11:57

score 3 · Answer 3 · answered Oct 24 '13 at 12:10

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Redirecting Qemu output to terminal might cause some problem (personally i don't like it). You can using options like -noframe (this will create new window but won't any window frame) or -curses to experience qemu output on terminal.

answered Oct 24 '13 at 12:10

rakib_

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redirect QEMU window output to terminal running qemu

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