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)