.\"  Copyright 2002 walter harms (walter.harms@informatik.uni-oldenburg.de)

.\"

.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)

.\" Distributed under GPL

.\" %%%LICENSE_END

.\"

.\"  adapted glibc info page

.\"

.\"  This should run as 'Guru Meditation' (amiga joke :)

.\"  The function is quite complex and deserves an example

.\"

.\"  Polished, aeb, 2003-11-01

.TH FMTMSG 3 2017-09-15 "" "Linux Programmer's Manual"

.SH NAME

fmtmsg \- print formatted error messages

.SH SYNOPSIS

.nf

.B #include <fmtmsg.h>

.PP

.BI "int fmtmsg(long " classification ", const char *" label ,

.BI "           int " severity ", const char *" text ,

.BI "           const char *" action ", const char *" tag );

.fi

.SH DESCRIPTION

This function displays a message described by its arguments on the device(s)

specified in the

.I classification

argument.

For messages written to

.IR stderr ,

the format depends on the

.B MSGVERB

environment variable.

.PP

The

.I 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.

.PP

The

.I text

argument describes the condition of the error.

.PP

The

.I action

argument describes possible steps to recover from the error.

If it is printed, it is prefixed by "TO FIX: ".

.PP

The

.I tag

argument is a reference to the online documentation where more

information can be found.

It should contain the

.I label

value and a unique identification number.

.SS Dummy arguments

Each of the arguments can have a dummy value.

The dummy classification value

.B MM_NULLMC

(0L) does not specify any output, so nothing is printed.

The dummy severity value

.B NO_SEV

(0) says that no severity is supplied.

The values

.BR MM_NULLLBL ,

.BR MM_NULLTXT ,

.BR MM_NULLACT ,

.B MM_NULLTAG

are synonyms for

.IR "((char\ *)\ 0)" ,

the empty string, and

.B MM_NULLSEV

is a synonym for

.BR NO_SEV .

.SS The classification argument

The

.I classification

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

.PP

The first value defines the output channel.

.TP 12n

.B MM_PRINT

Output to

.IR stderr .

.TP

.B MM_CONSOLE

Output to the system console.

.TP

.B "MM_PRINT | MM_CONSOLE"

Output to both.

.PP

The second value is the source of the error:

.TP 12n

.B MM_HARD

A hardware error occurred.

.TP

.B MM_FIRM

A firmware error occurred.

.TP

.B MM_SOFT

A software error occurred.

.PP

The third value encodes the detector of the problem:

.TP 12n

.B MM_APPL

It is detected by an application.

.TP

.B MM_UTIL

It is detected by a utility.

.TP

.B MM_OPSYS

It is detected by the operating system.

.PP

The fourth value shows the severity of the incident:

.TP 12n

.B MM_RECOVER

It is a recoverable error.

.TP

.B MM_NRECOV

It is a nonrecoverable error.

.SS The severity argument

The

.I severity

argument can take one of the following values:

.TP 12n

.B MM_NOSEV

No severity is printed.

.TP

.B MM_HALT

This value is printed as HALT.

.TP

.B MM_ERROR

This value is printed as ERROR.

.TP

.B MM_WARNING

This value is printed as WARNING.

.TP

.B MM_INFO

This value is printed as INFO.

.PP

The numeric values are between 0 and 4.

Using

.BR addseverity (3)

or the environment variable

.B SEV_LEVEL

you can add more levels and strings to print.

.SH RETURN VALUE

The function can return 4 values:

.TP 12n

.B MM_OK

Everything went smooth.

.TP

.B MM_NOTOK

Complete failure.

.TP

.B MM_NOMSG

Error writing to

.IR stderr .

.TP

.B MM_NOCON

Error writing to the console.

.SH ENVIRONMENT

The environment variable

.B MSGVERB

("message verbosity") can be used to suppress parts of

the output to

.IR 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".

.PP

The environment variable

.B 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

.BR fmtmsg ()

print nothing.

If the user puts

.B SEV_LEVEL

with a format like

.PP

.RS

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

.RE

.PP

in the environment of the process before the first call to

.BR fmtmsg (),

where each description is of the form

.PP

.RS

severity-keyword,level,printstring

.RE

.PP

then

.BR fmtmsg ()

will also accept the indicated values for the level (in addition to

the standard levels 0\(en4), and use the indicated printstring when

such a level occurs.

.PP

The severity-keyword part is not used by

.BR 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

.BR 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

.BR fmtmsg ().

.SH VERSIONS

.BR fmtmsg ()

is provided in glibc since version 2.1.

.SH ATTRIBUTES

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

.BR attributes (7).

.TS

allbox;

lb lb lbw23

l l l.

Interface	Attribute	Value

T{

.BR fmtmsg ()

T}	Thread safety	T{

glibc >= 2.16: MT-Safe

.br

glibc < 2.16: MT-Unsafe

T}

.TE

.PP

Before glibc 2.16, the

.BR fmtmsg ()

function uses a static variable that is not protected,

so it is not thread-safe.

.PP

Since glibc 2.16,

.\" Modified in commit 7724defcf8873116fe4efab256596861eef21a94

the

.BR fmtmsg ()

function uses a lock to protect the static variable, so it is thread-safe.

.SH CONFORMING TO

The functions

.BR fmtmsg ()

and

.BR addseverity (3),

and environment variables

.B MSGVERB

and

.B SEV_LEVEL

come from System V.

.PP

The function

.BR fmtmsg ()

and the environment variable

.B MSGVERB

are described in POSIX.1-2001 and POSIX.1-2008.

.SH 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.

.SH EXAMPLE

.EX

#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\en");

        break;

    case MM_NOMSG:

        printf("Nothing printed to stderr\en");

        break;

    case MM_NOCON:

        printf("No console output\en");

        break;

    default:

        printf("Unknown error from fmtmsg()\en");

    }

    exit(EXIT_SUCCESS);

}

.EE

.PP

The output should be:

.PP

.in +4n

.EX

util\-linux:mount: ERROR: unknown mount option

TO FIX: See mount(8).  util\-linux:mount:017

.EE

.in

.PP

and after

.PP

.in +4n

.EX

MSGVERB=text:action; export MSGVERB

.EE

.in

.PP

the output becomes:

.PP

.in +4n

.EX

unknown mount option

TO FIX: See mount(8).

.EE

.in

.PP

.SH SEE ALSO

.BR addseverity (3),

.BR perror (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.