Error when process run an instance of xterm with fork

Question

I am given the task of forking n processes.

For each process, it must start an instance of /bin/xterm

I am done with the part of generating n processes and opening the xterm instance.

I got this output when I tried running the program. (Error in bold)

Number of process to open is 1.

Child (1): 3457

/bin/xterm: Xt error: Can't open display:

/bin/xterm: DISPLAY is not set

My code is below.

I tried googleing for the error but I have no luck so far.

Any solutions?

#include<stdio.h>
#include<stdlib.h>

int main(int argc, char *argv[])
{
    int num = atoi(argv[1]);
    printf("Number of process to open is %d.\n", num);
    int pid;
    int i;

    for(i = 0; i < num; i++)
    {
        pid = fork();
        if(pid < 0) {
            printf("Error");
            exit(1);
        } else if (pid == 0) {
            printf("Child (%d): %d\n", i + 1, getpid());
            char * const argv[] = {"/bin/xterm", NULL};
            char * const envp[] = {NULL};
            int rc = execve ("/bin/xterm", argv, envp);
            exit(0); 
        } else  {
            wait(NULL);
        }
    }
    return 0;
}

Why do you want to assign value to argv[] while it is constant? — enedil, Feb 16 '14 at 09:29
@Nullpointer thanks for the tip. I will remove the wait(NULL).. :) — Lawrence Wong, Feb 16 '14 at 09:56

score 0 · Answer 1 · answered Feb 16 '14 at 09:20

0

The error was explained in the output you pasted:

 /bin/xterm: DISPLAY is not set

You need to set DISPLAY appropriately. Otherwise, it will have no way to know where to put its display.

Also, did you really want to wait for each child after creating it?

answered Feb 16 '14 at 09:20

David Schwartz

179,497
17
214
278

Just curious, how do i set the DISPLAY properly? – Lawrence Wong Feb 16 '14 at 09:59
It depends where you want to display to go. You need to set it to the name/location of the display you want `xterm` to output to. Use `setenv`. – David Schwartz Feb 16 '14 at 10:04

score 0 · Accepted Answer · answered Feb 16 '14 at 09:30

This little changed code works perfectly fine on my system:

    #include<stdio.h>
#include<stdlib.h>
#include<unistd.h>

int main(int argc, char *argv[])
{
    int num = atoi(argv[1]);
    printf("Number of process to open is %d.\n", num);
    int pid;
    int i;

    for(i = 0; i < num; i++)
    {
        pid = fork();
        if(pid < 0) {
            printf("Error");
            exit(1);
        } else if (pid == 0) {
      //printf("Child (%d): %d\n", i + 1, getpid());
            //char * const argv[] = {"/bin/xterm", NULL};
            //char * const envp[] = {NULL};
            execl("/usr/bin/xterm", "/usr/bin/xterm", NULL);
            //exit(0); 
        }else  {
            wait(NULL);
        }
    }
    return 0;
}

May I ask how do you do it with execve based on my code above? — Lawrence Wong, Feb 16 '14 at 10:43

Silver18020 · Answer 3 · 2022-06-02T22:53:36.730

0

Use

char *envp[] = {"TERM=vt100", "PATH=/bin:/usr/bin", "DISPLAY=:0.0",(char *) 0 };

Doing so you set the display on your machine.

Sorry I'm late.

edited Jun 02 '22 at 22:53

answered Jun 02 '22 at 22:43

Silver18020

25
6

Error when process run an instance of xterm with fork

3 Answers3