fmtmsg(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON

fmtmsg(3)               Library Functions Manual               fmtmsg(3)

NAME         top

       fmtmsg - print formatted error messages

LIBRARY         top

       Standard C library (libc, -lc)

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 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         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

              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().

ATTRIBUTES         top

       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.

STANDARDS         top

       fmtmsg()
       MSGVERB
              POSIX.1-2008.

HISTORY         top

       fmtmsg()
              System V.  POSIX.1-2001 and POSIX.1-2008.  glibc 2.1.

       MSGVERB
              System V.  POSIX.1-2001 and POSIX.1-2008.

       SEV_LEVEL
              System V.

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

SEE ALSO         top

       addseverity(3), perror(3)

COLOPHON         top

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Linux man-pages 6.9.1          2024-06-15                      fmtmsg(3)

Pages that refer to this page: addseverity(3)