1SETPGID(3P) POSIX Programmer's Manual SETPGID(3P)
2
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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20 The setpgid() function shall either join an existing process group or
21 create a new process group within the session of the calling process.
22 The process group ID of a session leader shall not change.
24 Upon successful completion, the process group ID of the process with a
26 process ID that matches pid shall be set to pgid.
27 As a special case, if pid is 0, the process ID of the calling process
29 shall be used. Also, if pgid is 0, the process ID of the indicated
30 process shall be used.
31
33 Upon successful completion, setpgid() shall return 0; otherwise, -1
34 shall be returned and errno shall be set to indicate the error.
35
37 The setpgid() function shall fail if:
38 EACCES The value of the pid argument matches the process ID of a child
40 process of the calling process and the child process has suc‐
41 cessfully executed one of the exec functions.
42 EINVAL The value of the pgid argument is less than 0, or is not a value
44 supported by the implementation.
45 EPERM The process indicated by the pid argument is a session leader.
47 EPERM The value of the pid argument matches the process ID of a child
49 process of the calling process and the child process is not in
50 the same session as the calling process.
51 EPERM The value of the pgid argument is valid but does not match the
53 process ID of the process indicated by the pid argument and
54 there is no process with a process group ID that matches the
55 value of the pgid argument in the same session as the calling
56 process.
57 ESRCH The value of the pid argument does not match the process ID of
59 the calling process or of a child process of the calling
60 process.
61 The following sections are informative.
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65 None.
66
68 None.
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71 The setpgid() function shall group processes together for the purpose
72 of signaling, placement in foreground or background, and other job con‐
73 trol actions.
74 The setpgid() function is similar to the setpgrp() function of 4.2 BSD,
76 except that 4.2 BSD allowed the specified new process group to assume
77 any value. This presents certain security problems and is more flexible
78 than necessary to support job control.
79 To provide tighter security, setpgid() only allows the calling process
81 to join a process group already in use inside its session or create a
82 new process group whose process group ID was equal to its process ID.
83 When a job control shell spawns a new job, the processes in the job
85 must be placed into a new process group via setpgid(). There are two
86 timing constraints involved in this action:
87 1. The new process must be placed in the new process group before the
89 appropriate program is launched via one of the exec functions.
90 2. The new process must be placed in the new process group before the
92 shell can correctly send signals to the new process group.
93 To address these constraints, the following actions are performed. The
95 new processes call setpgid() to alter their own process groups after
96 fork() but before exec. This satisfies the first constraint. Under 4.3
97 BSD, the second constraint is satisfied by the synchronization property
98 of vfork(); that is, the shell is suspended until the child has com‐
99 pleted the exec, thus ensuring that the child has completed the
100 setpgid(). A new version of fork() with this same synchronization
101 property was considered, but it was decided instead to merely allow the
102 parent shell process to adjust the process group of its child processes
103 via setpgid(). Both timing constraints are now satisfied by having
104 both the parent shell and the child attempt to adjust the process group
105 of the child process; it does not matter which succeeds first.
106 Since it would be confusing to an application to have its process group
108 change after it began executing (that is, after exec), and because the
109 child process would already have adjusted its process group before
110 this, the [EACCES] error was added to disallow this.
111 One non-obvious use of setpgid() is to allow a job control shell to
113 return itself to its original process group (the one in effect when the
114 job control shell was executed). A job control shell does this before
115 returning control back to its parent when it is terminating or suspend‐
116 ing itself as a way of restoring its job control ``state'' back to what
117 its parent would expect. (Note that the original process group of the
118 job control shell typically matches the process group of its parent,
119 but this is not necessarily always the case.)
120
122 None.
123
125 exec, getpgrp(), setsid(), tcsetpgrp()
126 The Base Definitions volume of POSIX.1‐2017, <sys_types.h>, <unistd.h>
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130 Portions of this text are reprinted and reproduced in electronic form
131 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
132 table Operating System Interface (POSIX), The Open Group Base Specifi‐
133 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
134 Electrical and Electronics Engineers, Inc and The Open Group. In the
135 event of any discrepancy between this version and the original IEEE and
136 The Open Group Standard, the original IEEE and The Open Group Standard
137 is the referee document. The original Standard can be obtained online
138 at http://www.opengroup.org/unix/online.html .
139 Any typographical or formatting errors that appear in this page are
141 most likely to have been introduced during the conversion of the source
142 files to man page format. To report such errors, see https://www.ker‐
143 nel.org/doc/man-pages/reporting_bugs.html .
144IEEE/The Open Group 2017 SETPGID(3P)