1SETPGID(3P) POSIX Programmer's Manual SETPGID(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 setpgid - set process group ID for job control
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15 #include <unistd.h>
16 int setpgid(pid_t pid, pid_t pgid);
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21 The setpgid() function shall either join an existing process group or
22 create a new process group within the session of the calling process.
23 The process group ID of a session leader shall not change. Upon suc‐
24 cessful completion, the process group ID of the process with a process
25 ID that matches pid shall be set to pgid. As a special case, if pid is
26 0, the process ID of the calling process shall be used. Also, if pgid
27 is 0, the process ID of the indicated process shall be used.
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30 Upon successful completion, setpgid() shall return 0; otherwise, -1
31 shall be returned and errno shall be set to indicate the error.
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34 The setpgid() function shall fail if:
35 EACCES The value of the pid argument matches the process ID of a child
37 process of the calling process and the child process has suc‐
38 cessfully executed one of the exec functions.
39 EINVAL The value of the pgid argument is less than 0, or is not a value
41 supported by the implementation.
42 EPERM The process indicated by the pid argument is a session leader.
44 EPERM The value of the pid argument matches the process ID of a child
46 process of the calling process and the child process is not in
47 the same session as the calling process.
48 EPERM The value of the pgid argument is valid but does not match the
50 process ID of the process indicated by the pid argument and
51 there is no process with a process group ID that matches the
52 value of the pgid argument in the same session as the calling
53 process.
54 ESRCH The value of the pid argument does not match the process ID of
56 the calling process or of a child process of the calling
57 process.
58 The following sections are informative.
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63 None.
64
66 None.
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69 The setpgid() function shall group processes together for the purpose
70 of signaling, placement in foreground or background, and other job con‐
71 trol actions.
72 The setpgid() function is similar to the setpgrp() function of 4.2 BSD,
74 except that 4.2 BSD allowed the specified new process group to assume
75 any value. This presents certain security problems and is more flexible
76 than necessary to support job control.
77 To provide tighter security, setpgid() only allows the calling process
79 to join a process group already in use inside its session or create a
80 new process group whose process group ID was equal to its process ID.
81 When a job control shell spawns a new job, the processes in the job
83 must be placed into a new process group via setpgid(). There are two
84 timing constraints involved in this action:
85 1. The new process must be placed in the new process group before the
87 appropriate program is launched via one of the exec functions.
88 2. The new process must be placed in the new process group before the
90 shell can correctly send signals to the new process group.
91 To address these constraints, the following actions are performed. The
93 new processes call setpgid() to alter their own process groups after
94 fork() but before exec. This satisfies the first constraint. Under 4.3
95 BSD, the second constraint is satisfied by the synchronization property
96 of vfork(); that is, the shell is suspended until the child has com‐
97 pleted the exec, thus ensuring that the child has completed the
98 setpgid(). A new version of fork() with this same synchronization prop‐
99 erty was considered, but it was decided instead to merely allow the
100 parent shell process to adjust the process group of its child processes
101 via setpgid(). Both timing constraints are now satisfied by having both
102 the parent shell and the child attempt to adjust the process group of
103 the child process; it does not matter which succeeds first.
104 Since it would be confusing to an application to have its process group
106 change after it began executing (that is, after exec), and because the
107 child process would already have adjusted its process group before
108 this, the [EACCES] error was added to disallow this.
109 One non-obvious use of setpgid() is to allow a job control shell to
111 return itself to its original process group (the one in effect when the
112 job control shell was executed). A job control shell does this before
113 returning control back to its parent when it is terminating or suspend‐
114 ing itself as a way of restoring its job control "state" back to what
115 its parent would expect. (Note that the original process group of the
116 job control shell typically matches the process group of its parent,
117 but this is not necessarily always the case.)
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120 None.
121
123 exec(), getpgrp(), setsid(), tcsetpgrp(), the Base Definitions volume
124 of IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
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127 Portions of this text are reprinted and reproduced in electronic form
128 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
129 -- Portable Operating System Interface (POSIX), The Open Group Base
130 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
131 Electrical and Electronics Engineers, Inc and The Open Group. In the
132 event of any discrepancy between this version and the original IEEE and
133 The Open Group Standard, the original IEEE and The Open Group Standard
134 is the referee document. The original Standard can be obtained online
135 at http://www.opengroup.org/unix/online.html .
136IEEE/The Open Group 2003 SETPGID(3P)