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       fmtmsg - print formatted error messages


       #include <fmtmsg.h>

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


       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.

                   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.


       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.


       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().


       fmtmsg() is provided in glibc since version 2.1.


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

       │InterfaceAttributeValue                   │
       │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.


       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.


       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.


       #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).


       addseverity(3), perror(3)


       This  page  is  part of release 5.05 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

                                            2017-09-15                                  FMTMSG(3)