svcadm(1M)을 검색하려면 섹션에서 1M 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
vfork(2)
vfork(2) System Calls vfork(2)
NAME
vfork, vforkx - spawn new process in a virtual memory efficient way
SYNOPSIS
#include <unistd.h>
pid_t vfork(void);
#include <sys/fork.h>
pid_t vforkx(int flags);
DESCRIPTION
The vfork() and vforkx() functions create a new process without fully
copying the address space of the old process. These functions are use‐
ful in instances where the purpose of a fork(2) operation is to create
a new system context for an execve() operation (see exec(2)).
Unlike with the fork() function, the child process borrows the parent's
memory and thread of control until a call to execve() or an exit
(either abnormally or by a call to _exit() (see exit(2)). Any modifica‐
tion made during this time to any part of memory in the child process
is reflected in the parent process on return from vfork() or vforkx().
The parent process is suspended while the child is using its resources.
In a multithreaded application, vfork() and vforkx() borrow only the
thread of control that called vfork() or vforkx() in the parent; that
is, the child contains only one thread. The use of vfork() or vforkx()
in multithreaded applications, however, is unsafe due to race condi‐
tions that can cause the child process to become deadlocked and conse‐
quently block both the child and parent process from execution indefi‐
nitely.
The vfork() and vforkx() functions can normally be used the same way as
fork() and forkx(), respectively. The calling procedure, however,
should not return while running in the child's context, since the even‐
tual return from vfork() or vforkx() in the parent would be to a stack
frame that no longer exists. The _exit() function should be used in
favor of exit(3C) if unable to perform an execve() operation, since
exit() will invoke all functions registered by atexit(3C) and will
flush and close standard I/O channels, thereby corrupting the parent
process's standard I/O data structures. Care must be taken in the child
process not to modify any global or local data that affects the behav‐
ior of the parent process on return from vfork() or vforkx(), unless
such an effect is intentional.
Unlike fork() and forkx(), fork handlers are not run when vfork() and
vforkx() are called.
The vfork() and vforkx() functions are deprecated. Their sole legiti‐
mate use as a prelude to an immediate call to a function from the exec
family can be achieved safely by posix_spawn(3C) or posix_spawnp(3C).
Fork Extensions
The vforkx() function accepts a flags argument consisting of a bitwise
inclusive-OR of zero or more of the following flags, which are defined
in the header <sys/fork.h>:
FORK_NOSIGCHLD
FORK_WAITPID
See fork(2) for descriptions of these flags. If the flags argument is
0, vforkx() is identical to vfork().
RETURN VALUES
Upon successful completion, vfork() and vforkx() return 0 to the child
process and return the process ID of the child process to the parent
process. Otherwise, −1 is returned to the parent process, no child
process is created, and errno is set to indicate the error.
ERRORS
The vfork() and vforkx() functions will fail if:
EAGAIN The system-imposed limit on the total number of processes
under execution (either system-quality or by a single user)
would be exceeded. This limit is determined when the system
is generated.
ENOMEM There is insufficient swap space for the new process.
The vforkx() function will fail if:
EINVAL The flags argument is invalid.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityObsolete _ MT-LevelUnsafe
SEE ALSO
exec(2), exit(2), fork(2), ioctl(2), atexit(3C), exit(3C),
posix_spawn(3C), posix_spawnp(3C), wait(3C), signal.h(3HEAD),
attributes(7), standards(7)
NOTES
To avoid a possible deadlock situation, processes that are children in
the middle of a vfork() or vforkx() are never sent SIGTTOU or SIGTTIN
signals; rather, output or ioctls are allowed and input attempts result
in an EOF indication.
To forestall parent memory corruption due to race conditions with sig‐
nal handling, vfork() and vforkx() treat signal handlers in the child
process in the same manner as the exec(2) functions: signals set to be
caught by the parent process are set to the default action (SIG_DFL) in
the child process (see signal.h(3HEAD)). Any attempt to set a signal
handler in the child before execve() to anything other than SIG_DFL or
SIG_IGN is disallowed and results in setting the handler to SIG_DFL.
On some systems, the implementation of vfork() and vforkx() causes the
parent to inherit register values from the child. This can create prob‐
lems for certain optimizing compilers if <unistd.h> is not included in
the source calling vfork() or if <sys/fork.h> is not included in the
source calling vforkx().
The design of posix_spawn(3C) avoids many of the issues that can occur
during the window between vfork and exec system calls. When possible,
the use of posix_spawn(3C) is recommended, in preference to the vfork
functions documented here.
Oracle Solaris 11.4 27 Mar 2020 vfork(2)