1VFORK(2) Linux Programmer's Manual VFORK(2)
2
6 vfork - create a child process and block parent
7
9 #include <sys/types.h>
10 #include <unistd.h>
11 pid_t vfork(void);
13 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
15 vfork():
17 Since glibc 2.12:
18 (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
19 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
20 || /* Glibc versions <= 2.19: */ _BSD_SOURCE
21 Before glibc 2.12:
22 _BSD_SOURCE || _XOPEN_SOURCE >= 500
23
25 Standard description
26 (From POSIX.1) The vfork() function has the same effect as fork(2),
27 except that the behavior is undefined if the process created by vfork()
28 either modifies any data other than a variable of type pid_t used to
29 store the return value from vfork(), or returns from the function in
30 which vfork() was called, or calls any other function before success‐
31 fully calling _exit(2) or one of the exec(3) family of functions.
32 Linux description
34 vfork(), just like fork(2), creates a child process of the calling
35 process. For details and return value and errors, see fork(2).
36 vfork() is a special case of clone(2). It is used to create new pro‐
38 cesses without copying the page tables of the parent process. It may
39 be useful in performance-sensitive applications where a child is cre‐
40 ated which then immediately issues an execve(2).
41 vfork() differs from fork(2) in that the calling thread is suspended
43 until the child terminates (either normally, by calling _exit(2), or
44 abnormally, after delivery of a fatal signal), or it makes a call to
45 execve(2). Until that point, the child shares all memory with its par‐
46 ent, including the stack. The child must not return from the current
47 function or call exit(3) (which would have the effect of calling exit
48 handlers established by the parent process and flushing the parent's
49 stdio(3) buffers), but may call _exit(2).
50 As with fork(2), the child process created by vfork() inherits copies
52 of various of the caller's process attributes (e.g., file descriptors,
53 signal dispositions, and current working directory); the vfork() call
54 differs only in the treatment of the virtual address space, as
55 described above.
56 Signals sent to the parent arrive after the child releases the parent's
58 memory (i.e., after the child terminates or calls execve(2)).
59 Historic description
61 Under Linux, fork(2) is implemented using copy-on-write pages, so the
62 only penalty incurred by fork(2) is the time and memory required to
63 duplicate the parent's page tables, and to create a unique task struc‐
64 ture for the child. However