Ubuntu Manpage: fmtmsg - print formatted error messages

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 written 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 message  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 severity levels.  By default, only the
       five severity levels described above are available.  Any other numeric value would  make  fmtmsg()  print
       nothing.  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).

COLOPHON

       This  page  is  part  of  release  4.15  of  the  Linux man-pages project.  A description of the project,
       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.

                                                   2017-09-15                                          FMTMSG(3)