c - SIGCHLD causing segmentation fault, not going into handler -

i'm trying make simple shell , adding in functionality run processes in background &. in main method have:

int main() {   if (signal(sigchld, handle) == sig_err)     perror("cannot catch sigchld");   pid_t child = fork();   if (child == 0)     execvp(command, arguments);   else {     if (background == 1) {        printf("1");        backgroundlist(command, child);        printf("2"); }     else        waitpid(child, null, 0);   } } 

and handler have:

void handle(int s) {   printf("a");   if (signal(sigchld, handle) == sig_err)     perror("cannot catch sigchld");   pid_t pid;   printf("b");   while((pid = waitpid(0, null, wnohang)) > 0) {     printf("c");     rmbackgroundlist(pid);     printf("d");   } } 

i can can have run process in foreground fine. running "ls" has contents print screen, "a" , "b" printed since goes sigchld handler, doesn't go "c" since it's been waited on.

however, running in background ("ls&") print "1" , "2", have parent go prompt, child print contents screen, segmentation fault. not print of letters have in handler.

i cannot figure out why sigchld children waited on causes segmentation fault , never goes handler processes not waited on.

you not following rules signal handler. can't use printf() or perror(). read rules on safe in signal handler.

also behavior of signal() changes depending on if it's bsd or sysv style unix. linux changes behavior in glibc based on presence of _bsd_source or _gnu_source , changes depending on if call gcc -ansi or gcc -std=c99 or gcc -std=gnu99

you should using sigaction() instead of signal().