Fork system call - Revision history

Heth: /* What is fork */

2022-12-19T05:36:01Z

‎What is fork

2022-12-19T05:35:43Z

‎What is fork

2022-12-19T05:19:31Z

‎Magic or Qbit?

2022-12-19T05:18:58Z

2022-12-19T05:10:58Z

‎Use of fork

2022-12-17T09:50:59Z

‎Typical output when starting my_system

2022-12-17T09:48:59Z

‎Parent and child with different code

2022-12-17T09:37:44Z

‎start.c

2022-12-17T09:36:10Z

‎Parent and child with different code

2022-12-17T09:28:29Z

‎Links

@@ Line 50: / Line 50: @@
 </source>
 When running this code - different results can occur:
-source lang=bash>
+<source lang=bash>
 heth@emb3:~/bin/$ gcc process1.c -o process1
 heth@emb3:~/bin/$ ./process1

@@ Line 35: / Line 35: @@
 #include <unistd.h>
-int main(void) {
+         printf("Parent: PPID is %d and PID is %d\n", getppid(), getpid() );
-         if (fork() == 0) {
+         if ((pid=fork()) > 0) {
-                 printf("I am child  - my PPID is %d and my PID is %d\n", getppid(), getpid() );
+                 printf("Parent: PPID is %d and PID is %d\n", getppid(), getpid() );
-                 printf("Child  dying\n");
+                 printf("Parent: I got a child with PID %d\n", pid);
-                 return(0);
+        } else {
+         }
          return(0);
+}
 </source>

@@ Line 10: / Line 10: @@
 int main(void) {
          if (fork()) {
-                 printf("Sand\n");
+                 printf("True\n");
          } else {
-                 printf("Falsk\n");
+                 printf("False\n");
+         }
          return(0);
@@ Line 21: / Line 21: @@
 heth@emb3:~/bin/$ gcc process0.c -o process0
 heth@emb3:~/bin/$ ./process0
-Sand
+True
-Falsk
+False
 </source>
 ==What is fork==
 [[Fork system call|fork()]] creates a new process by duplicating the calling process.  The new process is referred to as the child process.  The calling process is referred to as the parent process.

@@ Line 17: / Line 17: @@
+}
 </source>
+When running the above code:
 [[Fork system call|fork()]] creates a new process by duplicating the calling process.  The new process is referred to as the child process.  The calling process is referred to as the parent process.
 *PID - Process ID - the ID of a running process
@@ Line 40: / Line 47: @@
+}
 </source>
-When running the above code:
 ==Example of creating a daemon in Linux==
 {{:Daemon linux}}

@@ Line 2: / Line 2: @@
 '''fork()''' is one of several functions to "spawn" a process
 =Use of fork=
 [[Fork system call|fork()]] creates a new process by duplicating the calling process.  The new process is referred to as the child process.  The calling process is referred to as the parent process.
 *PID - Process ID - the ID of a running process
 *PPID - Parent Process ID - default the ID of the process that created this process or 1 if the parent died.
 <source lang=c line>
 #include <stdio.h>
@@ Line 23: / Line 40: @@
+}
 </source>
+When running the above code:
 ==Example of creating a daemon in Linux==
 {{:Daemon linux}}

@@ Line 79: / Line 79: @@
 # '''client.c''' - contains the client code
 ==Typical output when starting my_system==
 <source lang=text>
 Starting server as parent - my PID is 2644553
@@ Line 92: / Line 95: @@
 Client signing out
 </source>
 ==my_system.c==
 <source lang=c line>

@@ Line 75: / Line 75: @@
 Three files:
-# '''start.c''' - forks and starts the server code as parent and the client code as child.
+# '''my_system.c''' - forks and starts the server code as parent and the client code as child.
 # '''server.c"' - contains the server code
 # '''client.c''' - contains the client code
-==start.c==
+==Typical output when starting my_system==
 <source lang=c line>
 #include <stdio.h>
@@ Line 120: / Line 134: @@
+{
          char buf[40]="hello";
-         int fd,i=0;
+         int fd,i;
          fd = atoi(argv[1]);
          printf("Server started my PID is %d\n", getpid());
-         while(i < 5)
+         for (i=1; i <= 5; i++) {
                  sprintf(buf,"hello: %d",i);
                  write(fd,buf,strlen(buf)+1);
@@ Line 132: / Line 144: @@
+         }
          buf[0] == 0;
-         write(fd,buf,1);
+         close(fd);
          puts("Server signing out");
@@ Line 156: / Line 168: @@
                  printf("Client received: %s\n",buf);
+         }
-         printf("Client signing out");
+        close(fd);
          return 0;
+}
 </source>
 </onlyinclude>

@@ Line 89: / Line 89: @@
          char argv[50];
          pipe(arr);
          if(fork())
+         {
@@ Line 109: / Line 108: @@
+}
 </source>
 ==server.c==
 <source lang=c line>

@@ Line 71: / Line 71: @@
 </source>
 =Parent and child with different code=
 If we want a parent and a child to execute different code and share a resource, for example a server that send information to a client.
@@ Line 159: / Line 160: @@
+}
 </source>
 =Links=
 *[https://devarea.com/linux-fork-system-call-and-its-pitfalls/#.Y5v3THbMJPY good article from devarea.com]
 [[Category:Linux]][[Category:C]]