How come I can't re-acquire the controlling terminal here

This is a discussion on How come I can't re-acquire the controlling terminal here within the Linux Programming forums, part of the Platform Specific Boards category; Code: #include <stdio.h> #include <unistd.h> #include <fcntl.h> #include <stdlib.h> void reterm(void) { pid_t pid; if((pid = fork()) < 0) { ...

  1. #1
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    How come I can't re-acquire the controlling terminal here

    Code:
    #include <stdio.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdlib.h>
    
    void reterm(void)
    {
      pid_t pid;
      if((pid = fork()) < 0) {
        fprintf(stderr, "can't fork\n");
        exit(1);
      }
    
      if(pid !=0)
        exit(1);
    
      if(setsid() < 0) {
        fprintf(stderr, "setsid error\n");
      }
    
    }
    
    int main(void)
    {
      int fd;
    
      reterm();
    
      if((fd = open("/dev/null", O_RDONLY | O_NOCTTY)) < 0) {
        fprintf(stderr, "can't open tty\n");
        exit(1);
      }
    
      sleep(5000);
      close(fd);
    
      return 0;
    }
    [cd@localhost oakland]$ gcc -Wall reterm.c -o reterm
    [cd@localhost oakland]$ ./reterm
    [cd@localhost oakland]$ ps waux | grep reterm
    cd 25021 0.0 0.0 1484 156 ? Ss 17:36 0:00 ./
    reterm
    cd 25031 0.0 0.1 3880 676 pts/3 R+ 17:36 0:00 grep
    reterm
    [cd@localhost oakland]$

  2. #2
    and the hat of wrongness Salem's Avatar
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    Since when was /dev/null a tty?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
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    Join Date
    May 2007
    Location
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    Well, if I change it to /dev/tty like in the following

    Code:
    #include <stdio.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdlib.h>
    #include <errno.h>
    
    void reterm(void)
    {
      pid_t pid;
    
      if((pid = fork()) < 0) {
        fprintf(stderr, "can't fork\n");
        exit(1);
      }
    
      if(pid !=0)
        exit(1);
    
      if(setsid() < 0) 
        fprintf(stderr, "setsid error\n");
    }
    
    int main(void) 
    {
    
      int fd;
    
      reterm();
    
      if((fd = open("/dev/tty", O_RDONLY | O_NOCTTY)) < 0) {
        perror("Can't open /dev/tty: ");
        exit(1);
      }
    
      sleep(5000);
      close(fd);
    
      return 0;
    }
    I get

    $ gcc -Wall reterm.c -o reterm
    $ ./reterm
    Can't open /dev/tty: : No such device or address
    $ ls -al /dev/tty
    crw-rw-rw- 1 root tty 5, 0 Aug 9 08:35 /dev/tty
    Last edited by Overworked_PhD; 08-12-2008 at 07:22 AM.

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