man2/setpgid.2

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  33 .\"     @(#)getpgrp.2   6.4 (Berkeley) 3/10/91
  34 .\"
  35 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
  36 .\" Modified 1995-04-15 by Michael Chastain <mec@shell.portal.com>:
  37 .\"   Added 'getpgid'.
  38 .\" Modified 1996-07-21 by Andries Brouwer <aeb@cwi.nl>
  39 .\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
  40 .\" Modified 1999-09-02 by Michael Haardt <michael@moria.de>
  41 .\" Modified 2002-01-18 by Michael Kerrisk <mtk.manpages@gmail.com>
  42 .\" Modified 2003-01-20 by Andries Brouwer <aeb@cwi.nl>
  43 .\" 2007-07-25, mtk, fairly substantial rewrites and rearrangements
  44 .\" of text.
  45 .\"
  46 .TH SETPGID 2 2010-09-26 "Linux" "Linux Programmer's Manual"
  47 .SH NAME
  48 setpgid, getpgid, setpgrp, getpgrp \- set/get process group
  49 .SH SYNOPSIS
  50 .B #include <unistd.h>
  51 .sp
  52 .BI "int setpgid(pid_t " pid ", pid_t " pgid );
  53 .br
  54 .BI "pid_t getpgid(pid_t " pid );
  55 .sp
  56 .BR "pid_t getpgrp(void);" "                 /* POSIX.1 version */"
  57 .br
  58 .BI "pid_t getpgrp(pid_t " pid ");\ \ \ \ \ \ \ \ \ \ \ "
  59 /* BSD version */
  60 .sp
  61 .BR "int setpgrp(void);" "                   /* System V version */"
  62 .br
  63 .BI "int setpgrp(pid_t " pid ", pid_t " pgid ");\ "
  64 /* BSD version */
  65 .sp
  66 .in -4n
  67 Feature Test Macro Requirements for glibc (see
  68 .BR feature_test_macros (7)):
  69 .in
  70 .sp
  71 .ad l
  72 .PD 0
  73 .BR getpgid ():
  74 .RS 4
  75 _XOPEN_SOURCE\ >=\ 500 ||
  76 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  77 .br
  78 || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
  79 .RE
  80 .sp
  81 .BR setpgrp "() (POSIX.1):"
  82 .nf
  83     _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  84     _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  85 .fi
  86 .sp
  87 .BR setpgrp "()\ (BSD),"
  88 .BR getpgrp "()\ (BSD):"
  89 .nf
  90     _BSD_SOURCE &&
  91         !\ (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
  92            _XOPEN_SOURCE_EXTENDED || _GNU_SOURCE || _SVID_SOURCE)
  93 .fi
  94 .PD
  95 .ad
  96 .SH DESCRIPTION
  97 All of these interfaces are available on Linux,
  98 and are used for getting and setting the
  99 process group ID (PGID) of a process.
 100 The preferred, POSIX.1-specified ways of doing this are:
 101 .BR getpgrp (void),
 102 for retrieving the calling process's PGID; and
 103 .BR setpgid (),
 104 for setting a process's PGID.
 105
 106 .BR setpgid ()
 107 sets the PGID of the process specified by
 108 .I pid
 109 to
 110 .IR pgid .
 111 If
 112 .I pid
 113 is zero, then the process ID of the calling process is used.
 114 If
 115 .I pgid
 116 is zero, then the PGID of the process specified by
 117 .I pid
 118 is made the same as its process ID.
 119 If
 120 .BR setpgid ()
 121 is used to move a process from one process
 122 group to another (as is done by some shells when creating pipelines),
 123 both process groups must be part of the same session (see
 124 .BR setsid (2)
 125 and
 126 .BR credentials (7)).
 127 In this case,
 128 the \fIpgid\fP specifies an existing process group to be joined and the
 129 session ID of that group must match the session ID of the joining process.
 130
 131 The POSIX.1 version of
 132 .BR getpgrp (),
 133 which takes no arguments,
 134 returns the PGID of the calling process.
 135
 136 .BR getpgid ()
 137 returns the PGID of the process specified by
 138 .IR pid .
 139 If
 140 .I pid
 141 is zero, the process ID of the calling process is used.
 142 (Retrieving the PGID of a process other than the caller is rarely
 143 necessary, and the POSIX.1
 144 .BR getpgrp ()
 145 is preferred for that task.)
 146
 147 The System V-style
 148 .BR setpgrp (),
 149 which takes no arguments, is equivalent to
 150 .IR "setpgid(0,\ 0)" .
 151
 152 The BSD-specific
 153 .BR setpgrp ()
 154 call, which takes arguments
 155 .I pid
 156 and
 157 .IR pgid ,
 158 is equivalent to
 159 .IR "setpgid(pid, pgid)" .
 160 .\" The true BSD setpgrp() system call differs in allowing the PGID
 161 .\" to be set to arbitrary values, rather than being restricted to
 162 .\" PGIDs in the same session.
 163
 164 The BSD-specific
 165 .BR getpgrp ()
 166 call, which takes a single
 167 .I pid
 168 argument, is equivalent to
 169 .IR "getpgid(pid)" .
 170 .SH RETURN VALUE
 171 On success,
 172 .BR setpgid ()
 173 and
 174 .BR setpgrp ()
 175 return zero.
 176 On error, \-1 is returned, and
 177 .I errno
 178 is set appropriately.
 179
 180 The POSIX.1
 181 .BR getpgrp ()
 182 always returns the PGID of the caller.
 183
 184 .BR getpgid (),
 185 and the BSD-specific
 186 .BR getpgrp ()
 187 return a process group on success.
 188 On error, \-1 is returned, and
 189 .I errno
 190 is set appropriately.
 191 .SH ERRORS
 192 .TP
 193 .B EACCES
 194 An attempt was made to change the process group ID
 195 of one of the children of the calling process and the child had
 196 already performed an
 197 .BR execve (2)
 198 .RB ( setpgid (),
 199 .BR setpgrp ()).
 200 .TP
 201 .B EINVAL
 202 .I pgid
 203 is less than 0
 204 .RB ( setpgid (),
 205 .BR setpgrp ()).
 206 .TP
 207 .B EPERM
 208 An attempt was made to move a process into a process group in a
 209 different session, or to change the process
 210 group ID of one of the children of the calling process and the
 211 child was in a different session, or to change the process group ID of
 212 a session leader
 213 .RB ( setpgid (),
 214 .BR setpgrp ()).
 215 .TP
 216 .B ESRCH
 217 For
 218 .BR getpgid ():
 219 .I pid
 220 does not match any process.
 221 For
 222 .BR setpgid ():
 223 .I pid
 224 is not the calling process and not a child of the calling process.
 225 .SH CONFORMING TO
 226 .BR setpgid ()
 227 and the version of
 228 .BR getpgrp ()
 229 with no arguments
 230 conform to POSIX.1-2001.
 231
 232 POSIX.1-2001 also specifies
 233 .BR getpgid ()
 234 and the version of
 235 .BR setpgrp ()
 236 that takes no arguments.
 237 (POSIX.1-2008 marks this
 238 .BR setpgrp ()
 239 specification as obsolete.)
 240
 241 The version of
 242 .BR getpgrp ()
 243 with one argument and the version of
 244 .BR setpgrp ()
 245 that takes two arguments derive from 4.2BSD,
 246 and are not specified by POSIX.1.
 247 .SH NOTES
 248 A child created via
 249 .BR fork (2)
 250 inherits its parent's process group ID.
 251 The PGID is preserved across an
 252 .BR execve (2).
 253
 254 Each process group is a member of a session and each process is a
 255 member of the session of which its process group is a member.
 256
 257 A session can have a controlling terminal.
 258 At any time, one (and only one) of the process groups
 259 in the session can be the foreground process group
 260 for the terminal;
 261 the remaining process groups are in the background.
 262 If a signal is generated from the terminal (e.g., typing the
 263 interrupt key to generate
 264 .BR SIGINT ),
 265 that signal is sent to the foreground process group.
 266 (See
 267 .BR termios (3)
 268 for a description of the characters that generate signals.)
 269 Only the foreground process group may
 270 .BR read (2)
 271 from the terminal;
 272 if a background process group tries to
 273 .BR read (2)
 274 from the terminal, then the group is sent a
 275 .B SIGTSTP
 276 signal, which suspends it.
 277 The
 278 .BR tcgetpgrp (3)
 279 and
 280 .BR tcsetpgrp (3)
 281 functions are used to get/set the foreground
 282 process group of the controlling terminal.
 283
 284 The
 285 .BR setpgid ()
 286 and
 287 .BR getpgrp ()
 288 calls are used by programs such as
 289 .BR bash (1)
 290 to create process groups in order to implement shell job control.
 291
 292 If a session has a controlling terminal, and the
 293 .B CLOCAL
 294 flag for that terminal is not set,
 295 and a terminal hangup occurs, then the session leader is sent a
 296 .BR SIGHUP .
 297 If the session leader exits, then a
 298 .B SIGHUP
 299 signal will also be sent to each process in the foreground
 300 process group of the controlling terminal.
 301
 302 If the exit of the process causes a process group to become orphaned,
 303 and if any member of the newly orphaned process group is stopped, then a
 304 .B SIGHUP
 305 signal followed by a
 306 .B SIGCONT
 307 signal will be sent to each process
 308 in the newly orphaned process group.
 309 .\" exit.3 refers to the following text:
 310 An orphaned process group is one in which the parent of
 311 every member of process group is either itself also a member
 312 of the process group or is a member of a process group
 313 in a different session (see also
 314 .BR credentials (7)).
 315 .SH SEE ALSO
 316 .BR getuid (2),
 317 .BR setsid (2),
 318 .BR tcgetpgrp (3),
 319 .BR tcsetpgrp (3),
 320 .BR termios (3),
 321 .BR credentials (7)