1CLONE(2) Linux Programmer's Manual CLONE(2)
2
6 clone, __clone2 - create a child process
7
9 #define _GNU_SOURCE
10 #include <sched.h>
11 int clone(int (*fn)(void *), void *child_stack,
13 int flags, void *arg, ...
14 /* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );
15
17 clone() creates a new process, in a manner similar to fork(2). It is
18 actually a library function layered on top of the underlying clone()
19 system call, hereinafter referred to as sys_clone. A description of
20 sys_clone is given towards the end of this page.
21 Unlike fork(2), these calls allow the child process to share parts of
23 its execution context with the calling process, such as the memory
24 space, the table of file descriptors, and the table of signal handlers.
25 (Note that on this manual page, "calling process" normally corresponds
26 to "parent process". But see the description of CLONE_PARENT below.)
27 The main use of clone() is to implement threads: multiple threads of
29 control in a program that run concurrently in a shared memory space.
30 When the child process is created with clone(), it executes the func‐
32 tion application fn(arg). (This differs from fork(2), where execution
33 continues in the child from the point of the fork(2) call.) The fn
34 argument is a pointer to a function that is called by the child process
35 at the beginning of its execution. The arg argument is passed to the
36 fn function.
37 When the fn(arg) function application returns, the child process termi‐
39 nates. The integer returned by fn is the exit code for the child
40 process. The child process may also terminate explicitly by calling
41 exit(2) or after receiving a fatal signal.
42 The child_stack argument specifies the location of the stack used by
44 the child process. Since the child and calling process may share mem‐
45 ory, it is not possible for the child process to execute in the same
46 stack as the calling process. The calling process must therefore set
47 up memory space for the child stack and pass a pointer to this space to
48 clone(). Stacks grow downwards on all processors that run Linux
49 (except the HP PA processors), so child_stack usually points to the
50 topmost address of the memory space set up for the child stack.
51 The low byte of flags contains the number of the termination signal
53 sent to the parent when the child dies. If this signal is specified as
54 anything other than SIGCHLD, then the parent process must specify the
55 __WALL or __WCLONE options when waiting for the child with wait(2). If
56 no signal is specified, then the parent process is not signaled when
57 the child terminates.
58 flags may also be bitwise-or'ed with zero or more of the following con‐