diff options
Diffstat (limited to 'man2/fork.2')
| -rw-r--r-- | man2/fork.2 | 348 |
1 files changed, 0 insertions, 348 deletions
diff --git a/man2/fork.2 b/man2/fork.2 deleted file mode 100644 index b5a7816a0..000000000 --- a/man2/fork.2 +++ /dev/null @@ -1,348 +0,0 @@ -.\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> -.\" A few fragments remain from an earlier (1992) page by -.\" Drew Eckhardt (drew@cs.colorado.edu), -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" Modified by Michael Haardt (michael@moria.de) -.\" Modified Sat Jul 24 13:22:07 1993 by Rik Faith (faith@cs.unc.edu) -.\" Modified 21 Aug 1994 by Michael Chastain (mec@shell.portal.com): -.\" Referenced 'clone(2)'. -.\" Modified 1995-06-10, 1996-04-18, 1999-11-01, 2000-12-24 -.\" by Andries Brouwer (aeb@cwi.nl) -.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Added notes on capability requirements -.\" 2006-09-04, Michael Kerrisk -.\" Greatly expanded, to describe all attributes that differ -.\" parent and child. -.\" -.TH fork 2 (date) "Linux man-pages (unreleased)" -.SH NAME -fork \- create a child process -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <unistd.h> -.P -.B pid_t fork(void); -.fi -.SH DESCRIPTION -.BR fork () -creates a new process by duplicating the calling process. -The new process is referred to as the -.I child -process. -The calling process is referred to as the -.I parent -process. -.P -The child process and the parent process run in separate memory spaces. -At the time of -.BR fork () -both memory spaces have the same content. -Memory writes, file mappings -.RB ( mmap (2)), -and unmappings -.RB ( munmap (2)) -performed by one of the processes do not affect the other. -.P -The child process is an exact duplicate of the parent -process except for the following points: -.IP \[bu] 3 -The child has its own unique process ID, -and this PID does not match the ID of any existing process group -.RB ( setpgid (2)) -or session. -.IP \[bu] -The child's parent process ID is the same as the parent's process ID. -.IP \[bu] -The child does not inherit its parent's memory locks -.RB ( mlock (2), -.BR mlockall (2)). -.IP \[bu] -Process resource utilizations -.RB ( getrusage (2)) -and CPU time counters -.RB ( times (2)) -are reset to zero in the child. -.IP \[bu] -The child's set of pending signals is initially empty -.RB ( sigpending (2)). -.IP \[bu] -The child does not inherit semaphore adjustments from its parent -.RB ( semop (2)). -.IP \[bu] -The child does not inherit process-associated record locks from its parent -.RB ( fcntl (2)). -(On the other hand, it does inherit -.BR fcntl (2) -open file description locks and -.BR flock (2) -locks from its parent.) -.IP \[bu] -The child does not inherit timers from its parent -.RB ( setitimer (2), -.BR alarm (2), -.BR timer_create (2)). -.IP \[bu] -The child does not inherit outstanding asynchronous I/O operations -from its parent -.RB ( aio_read (3), -.BR aio_write (3)), -nor does it inherit any asynchronous I/O contexts from its parent (see -.BR io_setup (2)). -.P -The process attributes in the preceding list are all specified -in POSIX.1. -The parent and child also differ with respect to the following -Linux-specific process attributes: -.IP \[bu] 3 -The child does not inherit directory change notifications (dnotify) -from its parent -(see the description of -.B F_NOTIFY -in -.BR fcntl (2)). -.IP \[bu] -The -.BR prctl (2) -.B PR_SET_PDEATHSIG -setting is reset so that the child does not receive a signal -when its parent terminates. -.IP \[bu] -The default timer slack value is set to the parent's -current timer slack value. -See the description of -.B PR_SET_TIMERSLACK -in -.BR prctl (2). -.IP \[bu] -Memory mappings that have been marked with the -.BR madvise (2) -.B MADV_DONTFORK -flag are not inherited across a -.BR fork (). -.IP \[bu] -Memory in address ranges that have been marked with the -.BR madvise (2) -.B MADV_WIPEONFORK -flag is zeroed in the child after a -.BR fork (). -(The -.B MADV_WIPEONFORK -setting remains in place for those address ranges in the child.) -.IP \[bu] -The termination signal of the child is always -.B SIGCHLD -(see -.BR clone (2)). -.IP \[bu] -The port access permission bits set by -.BR ioperm (2) -are not inherited by the child; -the child must turn on any bits that it requires using -.BR ioperm (2). -.P -Note the following further points: -.IP \[bu] 3 -The child process is created with a single thread\[em]the -one that called -.BR fork (). -The entire virtual address space of the parent is replicated in the child, -including the states of mutexes, condition variables, -and other pthreads objects; the use of -.BR pthread_atfork (3) -may be helpful for dealing with problems that this can cause. -.IP \[bu] -After a -.BR fork () -in a multithreaded program, -the child can safely call only async-signal-safe functions (see -.BR signal\-safety (7)) -until such time as it calls -.BR execve (2). -.IP \[bu] -The child inherits copies of the parent's set of open file descriptors. -Each file descriptor in the child refers to the same -open file description (see -.BR open (2)) -as the corresponding file descriptor in the parent. -This means that the two file descriptors share open file status flags, -file offset, -and signal-driven I/O attributes (see the description of -.B F_SETOWN -and -.B F_SETSIG -in -.BR fcntl (2)). -.IP \[bu] -The child inherits copies of the parent's set of open message -queue descriptors (see -.BR mq_overview (7)). -Each file descriptor in the child refers to the same -open message queue description -as the corresponding file descriptor in the parent. -This means that the two file descriptors share the same flags -.RI ( mq_flags ). -.IP \[bu] -The child inherits copies of the parent's set of open directory streams (see -.BR opendir (3)). -POSIX.1 says that the corresponding directory streams -in the parent and child -.I may -share the directory stream positioning; -on Linux/glibc they do not. -.SH RETURN VALUE -On success, the PID of the child process is returned in the parent, -and 0 is returned in the child. -On failure, \-1 is returned in the parent, -no child process is created, and -.I errno -is set to indicate the error. -.SH ERRORS -.TP -.B EAGAIN -.\" NOTE! The following should match the description in pthread_create(3) -A system-imposed limit on the number of threads was encountered. -There are a number of limits that may trigger this error: -.RS -.IP \[bu] 3 -the -.B RLIMIT_NPROC -soft resource limit (set via -.BR setrlimit (2)), -which limits the number of processes and threads for a real user ID, -was reached; -.IP \[bu] -the kernel's system-wide limit on the number of processes and threads, -.IR /proc/sys/kernel/threads\-max , -was reached (see -.BR proc (5)); -.IP \[bu] -the maximum number of PIDs, -.IR /proc/sys/kernel/pid_max , -was reached (see -.BR proc (5)); -or -.IP \[bu] -the PID limit -.RI ( pids.max ) -imposed by the cgroup "process number" (PIDs) controller was reached. -.RE -.TP -.B EAGAIN -The caller is operating under the -.B SCHED_DEADLINE -scheduling policy and does not have the reset-on-fork flag set. -See -.BR sched (7). -.TP -.B ENOMEM -.BR fork () -failed to allocate the necessary kernel structures because memory is tight. -.TP -.B ENOMEM -An attempt was made to create a child process in a PID namespace -whose "init" process has terminated. -See -.BR pid_namespaces (7). -.TP -.B ENOSYS -.BR fork () -is not supported on this platform (for example, -.\" e.g., arm (optionally), blackfin, c6x, frv, h8300, microblaze, xtensa -hardware without a Memory-Management Unit). -.TP -.BR ERESTARTNOINTR " (since Linux 2.6.17)" -.\" commit 4a2c7a7837da1b91468e50426066d988050e4d56 -System call was interrupted by a signal and will be restarted. -(This can be seen only during a trace.) -.SH VERSIONS -.SS C library/kernel differences -Since glibc 2.3.3, -.\" nptl/sysdeps/unix/sysv/linux/fork.c -rather than invoking the kernel's -.BR fork () -system call, -the glibc -.BR fork () -wrapper that is provided as part of the -NPTL threading implementation invokes -.BR clone (2) -with flags that provide the same effect as the traditional system call. -(A call to -.BR fork () -is equivalent to a call to -.BR clone (2) -specifying -.I flags -as just -.BR SIGCHLD .) -The glibc wrapper invokes any fork handlers that have been -established using -.BR pthread_atfork (3). -.\" and does some magic to ensure that getpid(2) returns the right value. -.SH STANDARDS -POSIX.1-2008. -.SH HISTORY -POSIX.1-2001, SVr4, 4.3BSD. -.SH NOTES -Under Linux, -.BR fork () -is implemented using copy-on-write pages, so the only penalty that it incurs -is the time and memory required to duplicate the parent's page tables, -and to create a unique task structure for the child. -.SH EXAMPLES -See -.BR pipe (2) -and -.BR wait (2) -for more examples. -.P -.\" SRC BEGIN (fork.c) -.EX -#include <signal.h> -#include <stdint.h> -#include <stdio.h> -#include <stdlib.h> -#include <unistd.h> -\& -int -main(void) -{ - pid_t pid; -\& - if (signal(SIGCHLD, SIG_IGN) == SIG_ERR) { - perror("signal"); - exit(EXIT_FAILURE); - } - pid = fork(); - switch (pid) { - case \-1: - perror("fork"); - exit(EXIT_FAILURE); - case 0: - puts("Child exiting."); - exit(EXIT_SUCCESS); - default: - printf("Child is PID %jd\en", (intmax_t) pid); - puts("Parent exiting."); - exit(EXIT_SUCCESS); - } -} -.EE -.\" SRC END -.SH SEE ALSO -.BR clone (2), -.BR execve (2), -.BR exit (2), -.BR setrlimit (2), -.BR unshare (2), -.BR vfork (2), -.BR wait (2), -.BR daemon (3), -.BR pthread_atfork (3), -.BR capabilities (7), -.BR credentials (7) |