c system () function cause a segmentation fault

Question

I use the system function to execute a linux command in my device which use openwrt distribution as embedded OS.

int system(const char *command);

my program is like below

int check_file_dir(char *name)
{
    int i = 0;
    char command[128];
    sprintf(command, "ls /etc/config/%s &> /dev/null", name);
    printf("====> command =%s \n", command);
    i = system(command);
    return i;
}

void get_file_info () 
{
char name[128]; 
struct dirent *d_file;
struct stat attr;
char path[128];
char s_now[sizeof "AAAA-MM-JJTHH:MM:SS.000Z"];

   if ((dir = opendir ("/etc/config/")) != NULL) 
   {
        while ((d_file = readdir (dir)) != NULL) 
        {
            if(d_file->d_name[0] == '.')
                continue;
            sprintf(path, "/etc/config/%s", d_file->d_name);
            stat(path, &attr);
            strftime(s_now, sizeof s_now, "%Y-%m-%dT%H:%M:%S.000Z", localtime(&attr.st_mtime));
        }
    }
    closedir (dir);
    int j;
    for (j = 0; j< FILE_NUMBER; j++)
    {
       sprintf(name, "/etc/config/file%d", j); 
       if(check_file_dir(name) !=0)
           printf("file doesn't exist \n");
    }
}


 void main () 
{
get_file_info();
get_file_info();
}

the problem is cause by system function when get_file_info() is called twice!

they is any precautions to take to avoid system seg fault ?

Probably, buffer size is insufficient. Try to give `char command[]` more bytes. — V. Kravchenko, Jun 15 '16 at 09:34
I already do that increase the buf size to 512, but is the same problem — Anis_Stack, Jun 15 '16 at 09:36
http://stackoverflow.com/questions/19913446/why-should-the-system-function-be-avoided-in-c-and-c — Anis_Stack, Jun 15 '16 at 09:40
What is `get_name_from_conf`? Does that return a pointer to a constant? A value on the stack? Something on the heap? — John Burger, Jun 15 '16 at 09:40
`sprintf(path, "/etc/config/", d_file->d_name);` what is this? — Sourav Ghosh, Jun 15 '16 at 09:41
this link is explain why we have to avoid the use of system function — Anis_Stack, Jun 15 '16 at 09:41
@ Sourav Ghosh : the path variable will be use by stat function — Anis_Stack, Jun 15 '16 at 09:43
@Anis_Stack please double-check, this does not do anything meaningful... — Sourav Ghosh, Jun 15 '16 at 09:43
@Sourav Good point! @Anis_Stack, the second parameter to `sprintf()` needs some `%` modifiers: `"/etc/config/%s"` — John Burger, Jun 15 '16 at 09:44
Are you sure you can call `closedir (dir);` with `dir = NULL` ? — LPs, Jun 15 '16 at 09:54
Post your _actual_ code. `get_name_from_conf("/etc/config", &name)` won't even compile. — DaV, Jun 15 '16 at 09:54
@Anis_Stack Do us a favour: replace the call `get_name_from_conf(...);` with `name = "toto";` and run your program again. Does it work now? The reason I ask is that the rest _looks_ OK, while that whole loop looks suspicious. You call `get_name_from_conf` once, then enter a loop calling `check_file_dir()` repeatedly on the same `name` over and over... Does your real code actually modify `name`? Should `get_name_from_conf` be called inside the loop? — John Burger, Jun 15 '16 at 10:30
@Anis_Stack Perhaps the actual error is in the real code. If it is, noone here will find it. So you are better off posting the real code. — nos, Jun 15 '16 at 12:31

score 0 · Answer 1 · answered Jun 15 '16 at 12:25

I can't reproduce your issue because your code does not compile. This is a working version of your program with annotations of changes (and with testdir replacing /etc/config):

#include <limits.h> /* for PATH_MAX and LINE_MAX */
#include <stdio.h>  /* header include was missing */
#include <stdlib.h> /* header include was missing */
#include <time.h>   /* header include was missing */

#include <dirent.h>   /* header include was missing */
#include <sys/stat.h> /* header include was missing */

int check_file_dir(char *name)
{
    int i = 0;
    char command[LINE_MAX];  /* standard max command line length */
    /* path was wrong below */
    sprintf(command, "ls %s &> /dev/null", name);
    printf("====> command =%s \n", command);
    i = system(command);
    return i;
}

void get_file_info()
{
    char name[PATH_MAX]; /* standard max path length */
    struct dirent *d_file;
    struct stat attr;
    char path[PATH_MAX]; /* standard max path length */
    char s_now[sizeof "AAAA-MM-JJTHH:MM:SS.000Z"];
    DIR *dir;            /* declaration was missing */
    int FILE_NUMBER = 0; /* declaration was missing */

    if ((dir = opendir("testdir")) == NULL)
        return; /* no point to go on */

    while ((d_file = readdir(dir)) != NULL) {
        if (d_file->d_name[0] == '.')
            continue;
        sprintf(path, "testdir/%s", d_file->d_name);
        stat(path, &attr);
        strftime(s_now, sizeof s_now, "%Y-%m-%dT%H:%M:%S.000Z",
                 localtime(&attr.st_mtime)); /* not used? */
        ++FILE_NUMBER; /* assuming this is what you meant to do */
    }
    closedir(dir); /* was called even if !opendir() */

    int j;
    for (j = 0; j < FILE_NUMBER; j++) {
        sprintf(name, "testdir/file%d", j);
        if (check_file_dir(name) != 0)
            printf("file doesn't exist \n");
    }
}

int main(void) /* int and (void) */
{
    get_file_info();
    get_file_info();
    return 0; /* was missing */
}

score -2 · Answer 2 · edited May 23 '17 at 12:22

-2

according to this link How do I execute a Shell built-in command with a C function?

use execl("sh", "sh", "-c", command, NULL) instead of system

edited May 23 '17 at 12:22

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answered Jun 15 '16 at 10:32

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c system () function cause a segmentation fault

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