FORK(2)
NAME
fork − create a new process
USAGE
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. A lseek(2) on a descriptor in the child process, for example, can affect a subsequent read or write by the parent. The Shell uses this descriptor copying 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 zero; see setrlimit(2).
NOTES
You cannot fork a process that is acting as a mailbox server.
RETURN VALUE
Upon successful completion, fork returns a value of zero 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 either of the following is 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.