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FMTMSG(3) Linux Programmer's Manual FMTMSG(3)

NAME

     fmtmsg - print formatted error messages

SYNOPSIS

     #include <fmtmsg.h>

     int fmtmsg(long classification, const char *label,
                int severity, const char *text,
                const char *action, const char *tag);

DESCRIPTION

     This  function  displays  a  message  described by its arguments on the
     device(s) specified in the classification argument.  For messages writ-
     ten  to stderr, the format depends on the MSGVERB environment variable.

     The label argument identifies the source of the  message.   The  string
     must  consist of two colon separated parts where the first part has not
     more than 10 and the second part not more than 14 characters.

     The text argument describes the condition of the error.

     The action argument describes possible steps to recover from the error.
     If it is printed, it is prefixed by "TO FIX: ".

     The  tag argument is a reference to the online documentation where more
     information can be found.  It should contain  the  label  value  and  a
     unique identification number.

 Dummy arguments
     Each of the arguments can have a dummy value.  The dummy classification
     value MM_NULLMC (0L)  does  not  specify  any  output,  so  nothing  is
     printed.   The dummy severity value NO_SEV (0) says that no severity is
     supplied.  The values MM_NULLLBL,  MM_NULLTXT,  MM_NULLACT,  MM_NULLTAG
     are  synonyms  for  ((char *) 0), the empty string, and MM_NULLSEV is a
     synonym for NO_SEV.

 The classification argument
     The classification argument is the sum of values describing 4 types  of
     information.

     The first value defines the output channel.

     MM_PRINT    Output to stderr.

     MM_CONSOLE  Output to the system console.

     MM_PRINT | MM_CONSOLE
                 Output to both.

     The second value is the source of the error:

     MM_HARD     A hardware error occurred.

     MM_FIRM     A firmware error occurred.

     MM_SOFT     A software error occurred.

     The third value encodes the detector of the problem:

     MM_APPL     It is detected by an application.

     MM_UTIL     It is detected by a utility.

     MM_OPSYS    It is detected by the operating system.

     The fourth value shows the severity of the incident:

     MM_RECOVER  It is a recoverable error.

     MM_NRECOV   It is a nonrecoverable error.

 The severity argument
     The severity argument can take one of the following values:

     MM_NOSEV    No severity is printed.

     MM_HALT     This value is printed as HALT.

     MM_ERROR    This value is printed as ERROR.

     MM_WARNING  This value is printed as WARNING.

     MM_INFO     This value is printed as INFO.

     The  numeric  values  are between 0 and 4.  Using addseverity(3) or the
     environment variable SEV_LEVEL you can add more levels and  strings  to
     print.

RETURN VALUE

     The function can return 4 values:

     MM_OK       Everything went smooth.

     MM_NOTOK    Complete failure.

     MM_NOMSG    Error writing to stderr.

     MM_NOCON    Error writing to the console.

ENVIRONMENT

     The  environment  variable MSGVERB ("message verbosity") can be used to
     suppress parts of the output to stderr.  (It does not influence  output
     to  the console.)  When this variable is defined, is non-NULL, and is a
     colon-separated list of valid keywords, then only the parts of the mes-
     sage  corresponding  to  these keywords is printed.  Valid keywords are
     "label", "severity", "text", "action" and "tag".

     The environment variable SEV_LEVEL can be used to introduce new  sever-
     ity  levels.  By default, only the five severity levels described above
     are available.  Any other numeric value would make fmtmsg() print noth-
     ing.  If the user puts SEV_LEVEL with a format like

            SEV_LEVEL=[description[:description[:...]]]

     in  the  environment  of the process before the first call to fmtmsg(),
     where each description is of the form

            severity-keyword,level,printstring

     then fmtmsg() will also accept the indicated values for the  level  (in
     addition to the standard levels 0-4), and use the indicated printstring
     when such a level occurs.

     The severity-keyword part is not used by fmtmsg()  but  it  has  to  be
     present.   The  level part is a string representation of a number.  The
     numeric value must be a number greater than 4.  This value must be used
     in  the  severity argument of fmtmsg() to select this class.  It is not
     possible to overwrite any of the predefined classes.   The  printstring
     is  the  string  printed  when  a message of this class is processed by
     fmtmsg().

VERSIONS

     fmtmsg() is provided in glibc since version 2.1.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).

     +----------+---------------+-------------------------+
     |Interface | Attribute     | Value                   |
     +----------+---------------+-------------------------+
     |fmtmsg()  | Thread safety | glibc >= 2.16: MT-Safe  |
     |          |               | glibc < 2.16: MT-Unsafe |
     +----------+---------------+-------------------------+
     Before glibc 2.16, the fmtmsg() function uses a static variable that is
     not protected, so it is not thread-safe.

     Since  glibc  2.16,  the  fmtmsg()  function uses a lock to protect the
     static variable, so it is thread-safe.

CONFORMING TO

     The functions fmtmsg() and addseverity(3),  and  environment  variables
     MSGVERB and SEV_LEVEL come from System V.

     The   function  fmtmsg()  and  the  environment  variable  MSGVERB  are
     described in POSIX.1-2001 and POSIX.1-2008.

NOTES

     System V and UnixWare man pages tell us that these functions have  been
     replaced  by  "pfmt() and addsev()" or by "pfmt(), vpfmt(), lfmt(), and
     vlfmt()", and will be removed later.

EXAMPLE

     #include <stdio.h> #include <stdlib.h> #include <fmtmsg.h>

     int main(void) {
         long class = MM_PRINT | MM_SOFT | MM_OPSYS | MM_RECOVER;
         int err;

         err = fmtmsg(class, "util-linux:mount", MM_ERROR,
                     "unknown mount option", "See mount(8).",
                     "util-linux:mount:017");
         switch (err) {
         case MM_OK:
             break;
         case MM_NOTOK:
             printf("Nothing printed\n");
             break;
         case MM_NOMSG:
             printf("Nothing printed to stderr\n");
             break;
         case MM_NOCON:
             printf("No console output\n");
             break;
         default:
             printf("Unknown error from fmtmsg()\n");
         }
         exit(EXIT_SUCCESS); }

     The output should be:

         util-linux:mount: ERROR: unknown mount option TO FIX: See mount(8).
         util-linux:mount:017

     and after

         MSGVERB=text:action; export MSGVERB

     the output becomes:

         unknown mount option TO FIX: See mount(8).