NAME

       explain_setpgrp - explain setpgrp(2) errors

SYNOPSIS

       #include <libexplain/setpgrp.h>
       const char *explain_setpgrp(pid_t pid, pid_t pgid);
       const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);
       void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);
       void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid,
       pid_t pgid);

DESCRIPTION

       These functions may be used to obtain explanations for errors returned by  the  setpgrp(2)
       system call.

       Note:  the  setpgrp(2)  function  has  two  implementations.   The System V version has no
       arguments, while the BSD version has two arguments.  For simplicity of implementation, the
       argument list seen here includes the pid and pgid arguments.

       The  System V getpgid() semantics can be obtained by calling setpgrp(0, 0) on systems with
       the BSD version, and this is the API for libexplain, even on systems that do not  use  the
       BSD API.

   explain_setpgrp
       const char *explain_setpgrp(pid_t pid, pid_t pgid);

       The  explain_setpgrp function is used to obtain an explanation of an error returned by the
       setpgrp(2)  system  call.  The  least  the  message  will  contain   is   the   value   of
       strerror(errno),  but usually it will do much better, and indicate the underlying cause in
       more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Returns:
               The message explaining the error. This message buffer is shared by all  libexplain
               functions  which  do  not  supply  a  buffer in their argument list.  This will be
               overwritten by the next call to any libexplain function which shares this  buffer,
               including other threads.

       Note:  This  function  is  not  thread  safe, because it shares a return buffer across all
       threads, and many other functions in this library.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              if (setpgrp(pid, pgid) < 0)
              {
                  fprintf(stderr, "%s\n", explain_setpgrp(pid, pgid));
                  exit(EXIT_FAILURE);
              }

       The  above  code  example  is  available  pre-packaged  as  the  explain_setpgrp_or_die(3)
       function.

   explain_errno_setpgrp
       const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);

       The explain_errno_setpgrp function is used to obtain an explanation of an  error  returned
       by  the  setpgrp(2)  system  call.  The  least  the  message  will contain is the value of
       strerror(errno), but usually it will do much better, and indicate the underlying cause  in
       more detail.

       errnum  The  error  value  to  be decoded, usually obtained from the errno global variable
               just before this function is called. This is necessary if you  need  to  call  any
               code  between the system call to be explained and this function, because many libc
               functions will alter the value of errno.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Returns:
               The message explaining the error. This message buffer is shared by all  libexplain
               functions  which  do  not  supply  a  buffer in their argument list.  This will be
               overwritten by the next call to any libexplain function which shares this  buffer,
               including other threads.

       Note:  This  function  is  not  thread  safe, because it shares a return buffer across all
       threads, and many other functions in this library.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              if (setpgrp(pid, pgid) < 0)
              {
                  int err = errno;
                  fprintf(stderr, "%s\n", explain_errno_setpgrp(err, pid, pgid));
                  exit(EXIT_FAILURE);
              }

       The  above  code  example  is  available  pre-packaged  as  the  explain_setpgrp_or_die(3)
       function.

   explain_message_setpgrp
       void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);

       The explain_message_setpgrp function is used to obtain an explanation of an error returned
       by  the  setpgrp(2)  system  call.  The  least  the  message  will contain is the value of
       strerror(errno), but usually it will do much better, and indicate the underlying cause  in
       more detail.

       The errno global variable will be used to obtain the error value to be decoded.

       message The  location in which to store the returned message. If a suitable message return
               buffer is supplied, this function is thread safe.

       message_size
               The size in bytes of the location in which to store the returned message.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              if (setpgrp(pid, pgid) < 0)
              {
                  char message[3000];
                  explain_message_setpgrp(message, sizeof(message), pid, pgid);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       The  above  code  example  is  available  pre-packaged  as  the  explain_setpgrp_or_die(3)
       function.

   explain_message_errno_setpgrp
       void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid,
       pid_t pgid);

       The  explain_message_errno_setpgrp  function  is used to obtain an explanation of an error
       returned by the setpgrp(2) system call. The least the message will contain is the value of
       strerror(errno),  but usually it will do much better, and indicate the underlying cause in
       more detail.

       message The location in which to store the returned message. If a suitable message  return
               buffer is supplied, this function is thread safe.

       message_size
               The size in bytes of the location in which to store the returned message.

       errnum  The  error  value  to  be decoded, usually obtained from the errno global variable
               just before this function is called. This is necessary if you  need  to  call  any
               code  between the system call to be explained and this function, because many libc
               functions will alter the value of errno.

       pid     The original pid, exactly as passed to the setpgrp(2) system call.

       pgid    The original pgid, exactly as passed to the setpgrp(2) system call.

       Example: This function is intended to be used  in  a  fashion  similar  to  the  following
       example:
              if (setpgrp(pid, pgid) < 0)
              {
                  int err = errno;
                  char message[3000];
                  explain_message_errno_setpgrp(message, sizeof(message), err, pid, pgid);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       The  above  code  example  is  available  pre-packaged  as  the  explain_setpgrp_or_die(3)
       function.

SEE ALSO

       setpgrp(2)
               set process group

       explain_setpgrp_or_die(3)
               set process group and report errors

COPYRIGHT

       libexplain version 1.4
       Copyright (C) 2011 Peter Miller

                                                                               explain_setpgrp(3)