I am using ConEmu with the wslbridge.exe. I am incapable to pass down CTRL+C to cancel a grep that takes too long. Or an ls or any long command that displays stdout. I've followed this answer but still no result. Anyone faced this that can help me? For the record ^C is correctly passed in any other scenarios. This just happens with commands that display stdout output.
Thanks.
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Seems like a basic idea: I want to print out a prompt for a mini shell I am making in C. Here is an example of what I mean for the prompt:
$ ls
The $ being the "prompt". This little mini shell I am making supports backgrounding a process via the normal bash notation of putting a & symbol on the end of a line. Like $ ls &.
My logic currently is that in my main command loop, if the process is not going to be backgrounded then print out the prompt:
if(isBackground == 0)
prompt();
And then in my signal handler I print out the prompt using write() which covers the case of it being a background process.
This works fine if the background command returns right away like with a quick $ ls &, but in the case of something like $ sleep 10 & the shell will look like it is being blocked as the prompt will not be printed out until it hits the signal handler.
I can't figure out how to fix this because I don't know when the background process will end which means that the signal handler somehow needs to be saying when to print the new prompt because if the background process happened to have an output, it would output and then there would no longer be a prompt.
How can I resolve this problem? Is there a better way to do this that I'm not thinking of that could resolve my problem?
I'm going to run a regular program on a Linux-arm embedded device.
I tried to use system(cmd) function to run linux shell cmd in my program.
cmd would be a audio playing command "aplay -N sound.wav"
If cmd is as above, there will be no sound come out of my linux device, and the process of the program will in the T state (traced or stopped).
If cmd is set as "aplay -N sound.wav &", things will work just fine.
My question is what caused that, why does the "&" background parameter matter in this case.
Thanks.
If aplay allows for STDIN to act as a controller, running it forground may not provide the control input it expects. The backgrounding may detach STDIN and have aplay revert to default "play once until finished" mode. Do you have a man page for aplay?
I think i got why.
I'm running my qt program in the '&' mode, so I guess in any system(cmd), that cmd must contains a '&'.
I tried to run my qt program without the '&', after that, the cmd without '&' would be working fine.
So I guess the cause is you cannot run fork a foreground child process from a background father process.
I had an exercise to write a program that will do the following pipe processing:
ls -la | grep "^d" | more
After executing my program however, the bash interpreter would not break line nor display commands correctly, however after executing them the result is showed, it looks like the input for the console is not getting on stdout but somewhere else and i cant find the reason of this behavior.
I am using 3 child process with stdio redirected to connect the pipe between them.
The program finishes successfully it shows the good result, no errors are showed or whatever, also when i am using the cat instead of more everything works normally after execution, is it possible that more changes some system values and does not change them back?
It's likely that more is turning off echo and canonical mode on your TTY (see man 3 termios), and never switching them back on before it exits (either because it gets killed without a chance to, or because it doesn't think it's attached to a TTY). You can attach to more with gdb to find out why that's ahppening, or you could simply reset the terminal yourself before exiting.
The topic might sound weird, but here's what I want to achieve:
In Terminal A, type command line as following:
./create proA
The first process proA is created. It outputs something like
This is process A.
Open another terminal window (called Terminal B). In Terminal B, type the following line:
./create proB
The second process proB is created. It outputs:
This is process B.
UPDATED:
I'm trying to create two processes that communicate with each other. Before going into more details, I just want to try if I can create another process that has some relationship with first process when another terminal window is opened.
Is it possible to achieve something like this? If so, can someone give any tip for how to start in c? Thanks!
The terminals don't matter for inter process communication. There are so many ways to communicate between processes that it doesn't make sense to highlight any of them here.
About having a own terminal for each process. Well:
(xterm -e "${COMMANDLINE1}" &) ; (xterm -e "${COMMANDLINE2}" &)
if you want to see only errors, you should use:
./process > /dev/null 2>&1
if you did't understood 2>&1, read below)
possible numbers:
0 — STDIN, 1 — STDOUT and 2 — STDERR
that means, all std errors will be printed in std out.
I have written a program which I run after connecting to the box over SSH. It has some user interaction such as selecting options after being prompted, and usually I wait for the processes it carries out to finish before logging out which closes the terminal and ends the program. But now the process is quite lengthy and I don't want to wait whilst being logged in, so how could I implement a workaround for this in C please?
You can run a program in the background by following the command with "&"
wget -m www.google.com &
Or, you could use the "screen" program, that allows you to attach-deattach sessions
screen wget -m www.google.com
(PRESS CTRL+D)
screen -r (TO RE ATTACH)
http://linux.die.net/man/1/screen
The process is sent the HUP signal when the shell exits. All you have to do is install a signal handler that ignores SIGHUP.
Or just run the program using nohup.
The traditional way to do this is using the nohup(1) command:
nohup mycmd < /dev/null >& output.log &
Of course if you don't care about the output you can send it to /dev/null too, or you could take input from a file if you wanted.
Doing it this way will protect your process from a SIGHUP that would normally cause it to exit. You'll also want to redirect stdin/stdout/stderr like above, as you'll be ending your ssh session.
Syntax shown above is for bash.
you can use screen command. here is a tutorial. note you might need to install it to your systems.
There are many options :-) TIMTOWTDI… However, for your purposes, you might look into running a command-line utility such as dtach or GNU screen.
If you actually want to implement something in C, you could re-invent that wheel, but from your description of the problem, I doubt it should be necessary…
The actual C code to background a process is trivial:
//do interactive stuff...
if(fork())
exit(0);
//cool, I've been daemonized.
If you know the code will never wind up on a non-linux-or-BSD machine, you could even use daemon()
//interactive...
daemon(0, 0);
//background...