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SETPGID(2) System Calls Manual SETPGID(2)

setpgid, setpgrp
set process group

#include <unistd.h>
int
setpgid(pid_t pid, pid_t pgrp);
int
setpgrp(pid_t pid, pid_t pgrp);

setpgid() sets the process group of the specified process pid to the specified pgrp. If pid is zero, then the call applies to the current process. If pgrp is zero, the process ID of the specified process is used.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

setpgid() will fail and the process group will not be altered if:
 
 
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The value of the pid argument matches the process ID of a child process of the calling process, and the child process has successfully executed one of the exec functions.
 
 
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The value of the pgrp argument is less than zero.
 
 
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The requested process is a descendant of the calling process, and is either a session leader or not in the same session as the calling process.
 
 
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The value of the pgrp argument is neither the PID of the process indicated by the pid argument nor the process group ID of an existing process group in the same session as the calling process.
 
 
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The value of the pid argument does not match the process ID of the calling process or of a descendant of the calling process.

getpgrp(2), setsid(2)

setpgrp() is identical to setpgid(), and is retained for calling convention compatibility with historical versions of BSD.
The setpgid() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).
December 14, 2014 OpenBSD-current