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FMTMSG(3) Linux Programmer's Manual FMTMSG(3)
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.
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 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 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
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().
fmtmsg() is provided in glibc since version 2.1.
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.
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>
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).
addseverity(3), perror(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
2008-06-14 FMTMSG(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface