NAME

fork − create a new process

SYNOPSIS

pid = fork()
int pid;

DESCRIPTION

Fork causes creation of a new process.  The new process (child process) is an exact copy of the calling process except for the following:

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 descriptors. These descriptors reference the same underlying objects, so that, for instance, file pointers in file objects are shared between the child and the parent, so that a lseek(2) on a descriptor in the child process can affect a subsequent read or write by the parent.  This descriptor copying is also used by the shell to establish standard input and output for newly created processes as well as to set up pipes.  The child processes resource utilizations are set to 0; see setrlimit(2).

RETURN VALUE

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 the global variable errno is set to indicate the error. 

ERRORS

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 system-wide (nproc) or for an individual user (maxuprc) would be exceeded.  Nproc and maxuprc are kernel tuning parameters that can be adjusted via the “maxusers” and “options” rules of the kernel configuration file.  See the article “Building DYNIX Systems with Config” in Vol II. 

[ENOMEM] There is insufficient swap space for the new process. 

SEE ALSO

execve(2), wait(2)

4BSD