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28 .\" @(#)fork.2 8.1 (Berkeley) 6/4/93
36 .Nd create a new process
46 system call causes creation of a new process.
47 The new process (child process) is an exact copy of the
48 calling process (parent process) except for the following:
49 .Bl -bullet -offset indent
51 The child process has a unique process ID.
53 The child process has a different parent
54 process ID (i.e., the process ID of the parent process).
56 The child process has its own copy of the parent's descriptors,
57 except for descriptors returned by
59 which are not inherited from the parent process.
60 These descriptors reference the same underlying objects, so that,
61 for instance, file pointers in file objects are shared between
62 the child and the parent, so that an
64 on a descriptor in the child process can affect a subsequent
69 This descriptor copying is also used by the shell to
70 establish standard input and output for newly created processes
71 as well as to set up pipes.
73 The child process' resource utilizations
77 All interval timers are cleared; see
80 The child process has only one thread,
81 corresponding to the calling thread in the parent process.
82 If the process has more than one thread,
83 locks and other resources held by the other threads are not released
84 and therefore only async-signal-safe functions
87 are guaranteed to work in the child process until a call to
89 or a similar function.
92 Upon successful completion,
95 of 0 to the child process and returns the process ID of the child
96 process to the parent process.
97 Otherwise, a value of -1 is returned
98 to the parent process, no child process is created, and the global
101 is set to indicate the error.
105 system call will fail and no child process will be created if:
108 The system-imposed limit on the total
109 number of processes under execution would be exceeded.
110 The limit is given by the
114 (The limit is actually ten less than this
115 except for the super user).
117 The user is not the super user, and
118 the system-imposed limit
119 on the total number of
120 processes under execution by a single user would be exceeded.
121 The limit is given by the
124 .Dv KERN_MAXPROCPERUID .
126 The user is not the super user, and
127 the soft resource limit corresponding to the
131 would be exceeded (see
134 There is insufficient swap space for the new process.