I have a terminal that uses STDIN 3 (/proc/xxxx/fd/0 -> /dev/pts/3)
So if (in another terminal) I do:
echo 'do_something_command' > /dev/pts/3
The command is shown in my first (pts/3) terminal, but the command is not executed. And if (in this terminal pts/3) I'm in a program waiting for some data from stdin, the data is written on screen but the program does not capture it from stdin.
What I want to do is execute the command "do_something_command" and not only show it.
Can someone explain this behavior to me? How do I achieve my intention?
I completely get what you are asking. You can achieve this by writing and executing a small piece of code in C yourself. This should give you some idea.
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <string.h>
#include <unistd.h>
void print_help(char *prog_name) {
printf("Usage: %s [-n] DEVNAME COMMAND\n", prog_name);
printf("Usage: '-n' is an optional argument if you want to push a new line at the end of the text\n");
printf("Usage: Will require 'sudo' to run if the executable is not setuid root\n");
exit(1);
}
int main (int argc, char *argv[]) {
char *cmd, *nl = "\n";
int i, fd;
int devno, commandno, newline;
int mem_len;
devno = 1; commandno = 2; newline = 0;
if (argc < 3) {
print_help(argv[0]);
}
if (argc > 3 && argv[1][0] == '-' && argv[1][1] == 'n') {
devno = 2; commandno = 3; newline=1;
} else if (argc > 3 && argv[1][0] == '-' && argv[1][1] != 'n') {
printf("Invalid Option\n");
print_help(argv[0]);
}
fd = open(argv[devno],O_RDWR);
if(fd == -1) {
perror("open DEVICE");
exit(1);
}
mem_len = 0;
for (i = commandno; i < argc; i++) {
mem_len += strlen(argv[i]) + 2;
if (i > commandno) {
cmd = (char *)realloc((void *)cmd, mem_len);
} else { // i == commandno
cmd = (char *)malloc(mem_len);
}
strcat(cmd, argv[i]);
strcat(cmd, " ");
}
if (newline == 0)
usleep(225000);
for (i = 0; cmd[i]; i++)
ioctl (fd, TIOCSTI, cmd+i);
if (newline == 1)
ioctl (fd, TIOCSTI, nl);
close(fd);
free((void *)cmd);
exit (0);
}
Compile and execute it with sudo permissions. For example, if you want to execute a command on /dev/pts/3, then simply do a sudo ./a.out -n /dev/pts/3 whoami, runs a whoami on /dev/pts/3.
This code was completely taken from this page.
You seem to use the wrong quotes around the command.
Either remove the quotes and the echo command, or use echo and back-ticks (`).
Try:
echo `date` > /dev/pts/3
or just
date > /dev/pts/3
Note that whatever runs on /dev/pts/3 wouldn't be able to read what pops up "from behind".
Related
I want to run Emacs after logging into bash as user.
But also I want to be able to jump back into the bash prompt if I press CTRL-Z.
I have tried a couple of settings of .bashrc and .profile:
emacs
eval 'emacs'
bash -c emacs
exec emacs -nw
The problem is that all of this variants make CTRL-Z drop me not to bash prompt , but to empty stdin, like bash prompt was not loaded yet.
Any ideas? Thanks.
Thanks to Mark Plotnick, who answered below in comments. Using ioctl you can write to own tty.
c program:
#include "unistd.h"
#include "stdlib.h"
#include "stdio.h"
#include "sys/stat.h"
#include "sys/types.h"
#include "fcntl.h"
#include "termios.h"
#include "sys/ioctl.h"
int main(int argc, char ** argv)
{
if (argc >= 3)
{
int fd = open (argv[1], O_RDWR);
if (fd)
{
char * cmd = argv[2];
while(*cmd)
ioctl(fd, TIOCSTI, cmd++);
if (argc >= 4)
ioctl(fd, TIOCSTI, "\r");
return 0;
}
else
printf("could'n open file\n");
}
else
printf("wrong args\n");
return -1;
}
compile:
gcc my_ioctl.c -o my_ioctl
very end of .profile:
~/my_ioctl $(tty) emacs rr
(my c program does not care about what 3rd arg's actually is).
I actually have two questions but it seems they may be connected:
1) I've tried to run basic MPI example:
#include <mpi.h>
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char* argv[])
{
int rank, size;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
printf("I am %d from %d\n", rank, size);
MPI_Finalize();
return 0;
}
It has to output something like:
I am 0 from 2
I am 1 from 2
Although I'm getting the following:
$ mpicc mpi_hello.c -o hello
$ mpirun -np 4 ./hello
I am 0 from 1
I am 0 from 1
I am 0 from 1
I am 0 from 1
$ mpirun -np 2 ./hello
I am 0 from 1
I am 0 from 1
Is it somehow connected to thread definition in Linux? I'm running it on Ubuntu 16.04.
2) My OpenMP program:
#include <omp.h>
#include <math.h>
#include <time.h>
#include <iostream>
#include <stdio.h>
const int N = 10000;
int matrix[N][N];
int main()
{
#pragma omp parallel num_threads(2)
#pragma omp for
for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
matrix[i][j] = 1+i;
clock_t t;
t = clock();
#pragma omp parallel num_threads(2)
#pragma omp for
for (int i = 0; i < N; i++)
{
matrix[i][i] = 0;
for (int j = 0; j< N; j++)
if (j != i)
matrix[i][i] += sin(cos(log(matrix[i][j] + matrix[j][i])));
}
t = clock() - t;
std::cout << "It took " << ((float)t)/CLOCKS_PER_SEC << " sec" << std::endl;
return 0;
}
It works correctly and uses 2 threads. However, it loads 2 processors (~100% CPU) and takes the same time (~34 seconds) as the similiar consequtive one (loads 1 processor ~50% CPU). I know that OpenMP may need some time to start, but how can it result in the same duration of programs?
Answering to the MPI part of the question.
Do you have MPICH installed? If is that so, try to compile and run like this:
$ mpicc.mpich mpi_hello.c -o hello
$ mpirun.mpich -np 4 ./hello
I am 0 from 4
I am 1 from 4
I am 2 from 4
I am 3 from 4
It should work.
I'm trying to create a FIFO named pipe using the mknod() command:
int main() {
char* file="pipe.txt";
int state;
state = mknod(file, S_IFIFO & 0777, 0);
printf("%d",state);
return 0;
}
But the file is not created in my current directory. I tried listing it by ls -l . State returns -1.
I found similar questions here and on other sites and I've tried the solution that most suggested:
int main() {
char* file="pipe.txt";
int state;
unlink(file);
state = mknod(file, S_IFIFO & 0777, 0);
printf("%d",state);
return 0;
}
This made no difference though and the error remains. Am I doing something wrong here or is there some sort of system intervention which is causing this problem?
Help.. Thanks in advance
You are using & to set the file type instead of |. From the docs:
The file type for path is OR'ed into the mode argument, and the
application shall select one of the following symbolic
constants...
Try this:
state = mknod(file, S_IFIFO | 0777, 0);
Because this works:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main() {
char* file="pipe.txt";
int state;
unlink(file);
state = mknod(file, S_IFIFO | 0777, 0);
printf("state %d\n", state);
return 0;
}
Compile it:
gcc -o fifo fifo.c
Run it:
$ strace -e trace=mknod ./fifo
mknod("pipe.txt", S_IFIFO|0777) = 0
state 0
+++ exited with 0 +++
See the result:
$ ls -l pipe.txt
prwxrwxr-x. 1 lars lars 0 Jul 16 12:54 pipe.txt
I am trying to execute "word count" command on file given by absolute path - "/home/aaa/xxzz.txt" . I have closed the stdin so as to take input from file but the program doesn't give any output .
Also if I add some statement after "execve" command, it is also getting executed . Shouldn't the program exit after execve ?
int main()
{
char *envp[]={NULL };
int fd=open("/home/aaa/xxzz.txt",O_RDONLY);
close(0);
dup(fd);
char *param[]={ "/bin/wc",NULL } ;
execve("/bin/wc",param,envp);
}
Probably wc does not live in /bin (except for some systems which symlink that to /usr/bin, because wc normally lives in the latter). If I change the path in your example to /usr/bin/wc, it works for me:
#include <unistd.h>
#include <fcntl.h>
int
main()
{
char *envp[] = {NULL};
int fd = open("/home/aaa/xxzz.txt", O_RDONLY);
close(0);
dup(fd);
char *program = "/usr/bin/wc";
char *param[] = {program,NULL};
execve(program, param, envp);
}
I want to debug a console linux application with 2 xterm windows: one window used for gdb and another used for the application (e.g. mc).
What I do now is run 'tty && sleep 1024d' in the second xterm window (this gives me its pseudo-tty name) and then run 'tty ' in gdb to redirect the program to that other xterm window. However, GDB warns that it cannot set a controlling terminal and certain minor functions don't work (e.g. handling window resizing), as 'sleep 1024d' is still running on that xterm window.
Any better way to do it (rather than launching the process from the shell and attaching to it from gdb)?
I have somewhat modified the program given in a related bug to store the filename somewhere
http://sourceware.org/bugzilla/show_bug.cgi?id=11403
here is an example using it:
$ xterm -e './disowntty ~/tty.tmp' & sleep 1 && gdb --tty $(cat ~/tty.tmp) /usr/bin/links
/* tty;exec disowntty */
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <signal.h>
static void
end (const char *msg)
{
perror (msg);
for (;;)
pause ();
}
int
main (int argc, const char *argv[])
{
FILE *tty_name_file;
const char *tty_filename;
if (argc <= 1)
return 1;
else
tty_filename = argv[1];
void (*orig) (int signo);
setbuf (stdout, NULL);
orig = signal (SIGHUP, SIG_IGN);
if (orig != SIG_DFL)
end ("signal (SIGHUP)");
/* Verify we are the sole owner of the tty. */
if (ioctl (STDIN_FILENO, TIOCSCTTY, 0) != 0)
end ("TIOCSCTTY");
printf("%s %s\n", tty_filename, ttyname(STDIN_FILENO));
tty_name_file = fopen(tty_filename, "w");
fprintf(tty_name_file, "%s\n", ttyname(STDIN_FILENO));
fclose(tty_name_file);
/* Disown the tty. */
if (ioctl (STDIN_FILENO, TIOCNOTTY) != 0)
end ("TIOCNOTTY");
end ("OK, disowned");
return 1;
}