FORK(2) BSD Programmer's Manual FORK(2) NNAAMMEE ffoorrkk - create a new process SSYYNNOOPPSSIISS ##iinncclluuddee <<uunniissttdd..hh>> _p_i_d___t ffoorrkk(_v_o_i_d); DDEESSCCRRIIPPTTIIOONN FFoorrkk() causes creation of a new process. The new process (child process) is an exact copy of the calling process (parent process) except for the following: ++oo The child process has a unique process ID. ++oo The child process has a different parent process ID (i.e., the process ID of the parent process). ++oo 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 an lseek(2) on a de- scriptor 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 cre- ated processes as well as to set up pipes. ++oo The child processes resource utilizations are set to 0; see setrlimit(2). RREETTUURRNN VVAALLUUEESS Upon successful completion, ffoorrkk() returns a value of 0 to the child pro- cess and returns the process ID of the child process to the parent pro- cess. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable _e_r_r_n_o is set to indi- cate the error. EERRRROORRSS FFoorrkk() will fail and no child process will be created if: [EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration- dependent. [EAGAIN] The system-imposed limit MAXUPRC (<_s_y_s_/_p_a_r_a_m_._h>) on the total number of processes under execution by a single user would be exceeded. [ENOMEM] There is insufficient swap space for the new process. SSEEEE AALLSSOO execve(2), wait(2) HHIISSTTOORRYY A ffoorrkk(_2) function call appeared in Version 6 AT&T UNIX. 4th Berkeley Distribution June 4, 1993 1