fmtmsg(3) — Linux manual page


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

NAME         top

       fmtmsg - print formatted error messages

SYNOPSIS         top

       #include <fmtmsg.h>

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

DESCRIPTION         top

       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

       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.

                   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

RETURN VALUE         top

       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         top

       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


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


       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         top

       fmtmsg() is provided in glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │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         top

       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         top

       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.

EXAMPLES         top

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

           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).",
           switch (err) {
           case MM_OK:
           case MM_NOTOK:
               printf("Nothing printed\n");
           case MM_NOMSG:
               printf("Nothing printed to stderr\n");
           case MM_NOCON:
               printf("No console output\n");
               printf("Unknown error from fmtmsg()\n");

       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).

SEE ALSO         top

       addseverity(3), perror(3)

COLOPHON         top

       This page is part of release 5.08 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

                                 2020-06-09                        FMTMSG(3)

Pages that refer to this page: addseverity(3)