FORK(2) FORK(2)
NAME
fork - create a new process
SYNOPSIS
int fork ()
DESCRIPTION
fork causes creation of a new process. The new process
(child process) is an exact copy of the calling process
(parent process). This means the child process inherits the
following attributes from the parent process:
environment
close-on-exec flag [see exec(2)]
signal handling settings (i.e., SIGDFL, SIGIGN,
SIGHOLD, function address)
set-user-ID mode bit
set-group-ID mode bit
profiling on/off status
nice value [see nice(2)]
all attached shared memory segments [see shmop(2)]
process group ID
tty group ID [see exit(2)]
current working directory
root directory
file mode creation mask [see umask(2)]
file size limit [see ulimit(2)]
process session ID
The child process differs from the parent process in the
following ways:
The child process has a unique process ID.
The child process has a different parent process ID
(i.e., the process ID of the parent process).
The child process has its own copy of the parent's file
descriptors. Each of the child's file descriptors
shares a common file pointer with the corresponding
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FORK(2) FORK(2)
file descriptor of the parent.
All semadj values are cleared [see semop(2)].
Process locks, text locks and data locks are not
inherited by the child [see plock(2)].
The child process's utime, stime, cutime, and cstime
are set to 0. The time(s) left until an alarm clock
signal is reset to 0. [See setitimer(2)].
fork will fail and no child process will be created if one
or more of the following are true:
[EAGAIN] The system-imposed limit on the total number
of processes under execution would be
exceeded.
[EAGAIN] The system-imposed limit on the total number
of processes under execution by a single user
would be exceeded.
[EAGAIN] Total amount of system memory available when
reading via raw IO is temporarily
insufficient.
SEE ALSO
exec(2), nice(2), plock(2), ptrace(2), semop(2), shmop(2),
signal(2), sigset(2), times(2), ulimit(2), umask(2),
wait(2), setitimer(2).
DIAGNOSTICS
Upon successful completion, fork returns a value of 0 to the
child process and returns the process ID of the child
process to the parent process. Otherwise, a value of -1 is
returned to the parent process, no child process is created,
and errno is set to indicate the error.
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