I have a problem.I've written a program in C for armbian.
I am using RTKLIB software for GPS data conversion from ubx to RTCM3.
I get some data from serial port and start str2str(rtklib software).
It creates this command to run
str2str -in tcpsvr://:2101#ubx -out serial://ttyS2:115200#rtcm3
and call system function to run this command. It is successful, but when I send a new command, I want it to stop the str2str software.
I've tried the exit(0) and it stops my software. I don't want to stop my software. I want to stop str2str and create a new command and run it again.
How can I do it? I am not good with the linux environment.
Thanks
I suggest you find out how to search for the str2str process you want to kill, and get the PID. A stackoverflow search will reveal this and then use the PID to kill the process. Unless RTKLIB has a process to do this directly.
Related
This is a very beginner-level question in C.
Don't know where to start looking/searching.
So, if I have a program continuously running in C, what is the best way to accept input through the command line into the program?
EX, mysql is already running, but you can process a command call
mysql SELECT * FROM *
Do I need a different program to write to file/stdin?enter code here
Clarification:
So, mysql seems to be able to take in commands while it is already running... is that possible in C?
Goal:
I have some hooks into open gl es, and I want to run a continuous draw loop in the background, while having the ability to call commands such as
glhookprogram make "object1" model "triangle" program "default"
glhookprogram attr "object1" position "1.0, 1.0, 0.0" scale "2.0" rotation "45, 0, 0"
this way, I can have a node server run hw-accelerated animations in javascript on the rpi.
Looks like this is what you need (and I'm sorry - I won't be going into too much details as there are plenty of sources on the Web about that):
A "server" - that would be your background process that stays running in memory and can accept and process commands (requests)
A "client" - a (short-running?) process that can accept commands from user (GUI, command-line. Network? Other process?) and send requests to your "server"
This is not a trivial task for a beginner. I would suggest googling for "server-client" and for "inter-process communications" first and go from there.
The range of options to "accept input" into your server includes (but is not limited to) the following:
(Windows) messages
Shared memory and a command queue (producer-consumer)
Shared file (just listing it here for completeness, I'd advise against this particular one for your case)
Named pipes
Sockets (thanks for reminding me of those in the comments, can't believe I missed that!)
I'm trying to recode the UNIX command script (as it is on OSX). This is part of an exercise for school to help students learn UNIX APIs. We are only allowed to use system calls, more specifically, only those available on MAN(2) pages on Mac OSX (since that's our OS at school).
I have a 'first version' that kind of works. Running a program such as ls prints the right output to the screen and in an output file.
The problem scenario
I run bash from within the script-clone. First issue is I get the following error:
bash: no job control in this shell
I have tried forcing the bash process into foreground with setpgrp and setpgid but that din't change anything so I concluded that was not the problem.
I also tried to understand why the real script command uses cfmakeraw (at least on Linux), as seen here, but I don't get it. The MAN page is not very helpful.
The real script also dup2s STDIN on the slave, as seen here, but when I do that, it seems like input isn't read anymore.
However, the bash still runs, and I can execute commands inside of it.
But if I run vim inside it, and then hit Ctrl-Z to put vim to the background, the terminal is messed up (which does not happen when I'm in my regular terminal).
So I guess I must have done something wrong. I'd appreciate any advice/help.
Here's the source code:
https://github.com/conradkleinespel/unix-command-script/tree/2587b07e7a36dc74bf6dff0e82c9fdd33cb40411
You can compile by doing: make (it builds on OSX 10.9, hopefully on Linux as well)
And run by doing: ./ft_script
Don't know it it makes more sense to have all the source code in StackOverflow as it would crowd the page with it. If needed, I can replace the Git link with the source.
I don't use OS X, so I can't directly test your code, but I'm currently writing a toy terminal emulator and had similar troubles.
about "bash: no job control in this shell"
In order to perform job control, a shell needs to be a session leader and the controlling process of its terminal. By default, your program inherits the controlling terminal of your own shell which runs your script program and which is also a session leader. Here is how to make your new slave process a session leader after fork:
/* we don't need the inherited master fd */
close(master);
/* discard the previous controlling tty */
ioctl(0, TIOCNOTTY, 0);
/* replace existing stdin/out/err with the slave pts */
dup2(slave, 0);
dup2(slave, 1);
dup2(slave, 2);
/* discard the extra file descriptor for the slave pts */
close(slave);
/* make the pts our controlling terminal */
ioctl(0, TIOCSCTTY, 0);
/* make a new session */
setsid()
At this point, the forked process has stdin/out/err bound to the new pts, the pts became its controlling terminal, and the process is a session leader. The job control should now work.
about raw tty
When you run a program inside a normal terminal, it looks like this:
(term emulator, master side) <=> /dev/pts/42 <=> (program, slave side)
If you press ^Z, the terminal emulator will write the ascii character 0x1A to the pts. It is a control character, so it won't be sent to the program, but instead the kernel will issue SIGSTP to the program and suspend it. The process of transforming characters into something else is called "line cooking" and has various settings that can be adjusted for each tty.
Now let's look at the situation with script:
term emulator <=> /dev/pts/42 <=> script <=> /dev/pts/43 <=> program
With normal line settings, what happens when you press ^Z? It will be transformed into SIGSTP by /dev/pts/42 and script will be suspended. But that's not what we want, instead we'd like the 0x1A character produced by our ^Z to go as-is through /dev/pts/42, then be passed by script to /dev/pts/43 and only then be transformed into SIGSTP to suspend the program.
This is the reason why the pts between your terminal and script must be configured as "raw", so that all control characters reach the pts between script and the program, as if you were directly working with it.
So I have this old, nasty piece of C code that I inherited on this project from a software engineer that has moved on to greener pastures. The good news is... IT RUNS! Even better news is that it appears to be bug free.
The problem is that it was designed to run on a server with a set of start up parameters input on the command line. Now, there is a NEW requirement that this server is reconfigurable (didn't see that one coming...). Basically, if the server receives a command over UDP, it either starts this program, stops it, or restarts it with new start up parameters passed in via the UDP port.
Basically the code that I'm considering using to run the obfuscated program is something like this (sorry I don't have the actual source in front of me, it's 12:48AM and I can't sleep, so I hope the pseudo-code below will suffice):
//my "bad_process_manager"
int manage_process_of_doom() {
while(true) {
if (socket_has_received_data) {
int return_val = ParsePacket(packet_buffer);
// if statement ordering is just for demonstration, the real one isn't as ugly...
if (packet indicates shutdown) {
system("killall bad_process"); // process name is totally unique so I'm good?
} else if (packet indicates restart) {
system("killall bad_process"); // stop old configuration
// start with new parameters that were from UDP packet...
system("./my_bad_process -a new_param1 -b new_param2 &");
} else { // just start
system("./my_bad_process -a new_param1 -b new_param2 &");
}
}
}
So as a result of the system() calls that I have to make, I'm wondering if there's a neater way of doing so without all the system() calls. I want to make sure that I've exhausted all possible options without having to crack open the C file. I'm afraid that actually manipulating all these values on the fly would result in having to rewrite the whole file I've inherited since it was never designed to be configurable while the program is running.
Also, in terms of starting the process, am I correct to assume that throwing the "&" in the system() call will return immediately, just like I would get control of the terminal back if I ran that line from the command line? Finally, is there a way to ensure that stderr (and maybe even stdout) gets printed to the same terminal screen that the "manager" is running on?
Thanks in advance for your help.
What you need from the server:
Ideally your server process that you're controlling should be creating some sort of PID file. Also ideally, this server process should hold an exclusive lock on the PID file as long as it is still running. This allows us to know if the PID file is still valid or the server has died.
Receive shutdown message:
Try to get a lock on the PID file, if it succeeds, you have nothing to kill (the server has died, if you proceed to the kill regardless, you may kill the wrong process), just remove the old PID file.
If the lock fails, read the PID file and do a kill() on the PID, remove the old PID file.
Receive start message:
You'll need to fork() a new process, then choose your flavor of exec() to start the new server process. The server itself should of course recreate its PID file and take a lock on it.
Receive restart message:
Same as Shutdown followed by Start.
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...
I have written a program which calculates the amount of battery level available in my laptop. I have also defined a threshold value in the program. Whenever the battery level falls below threshold i would like to call another process. I have used system("./invoke.o") where invoke.o is the program that i have to run. I am running a script which runs the battery level checker program for every 5 seconds. Everything is working fine but when i close the bash shell the automatic invocation of invoke.o is not happening. How should i make the invoke.o to be invoked irrespective of whether bash is closed or not??. I am using UBUNTU LINUX
Try running it as: nohup ./myscript.sh, where the nohup command allows you to close the shell without terminating the process.
You could run your script as a cron job. This lets cron set up standard input and output for you, reschedule the job, and it will send you email if it fails.
The alternative is to run a script in the background with all input and output, including standard error output, redirected.
While you could make a proper daemon out of your program that kind of effort is probably not necessary.
man nohup
man upstart
man 2 setsid (more complex, leads to longer trail of breadcrumbs on daemon launching).