fmtmsg(3) Linux Programmer s Manual fmtmsg(3)

NAME fmtmsg - print formatted error messages

SYNOPSIS #include <fmtmsg.h>

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

DESCRIPTION This function displays a message described by its parameters on the device(s) specified in the classification parameter. For messages writ- ten to stderr, the format depends on the MSGVERB environment variable.

The label parameter 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 parameter describes the condition of the error.

The action parameter describes possible steps to recover from the error. If it is printed, it is prefixed by "TO FIX: ".

The tag parameter 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 parameters Each of the parameters 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 parameter The classification parameter 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 non-recoverable error.

The severity parameter The severity parameter 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() or the environment variable SEV_LEVEL you can add more levels and strings to print.

ENVIRONMENT 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 mes- sage 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 sever- ity levels. By default, only the five severity levels described above are available. Any other numeric value would make fmtmsg() print noth- ing. 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 parameter 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().

RETURN VALUES 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.

CONFORMING TO The functions fmtmsg() and addseverity(), 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.

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.

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

int main() { 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 printed0); break; case MM_NOMSG: printf("Nothing printed to stderr0); break; case MM_NOCON: printf("No console output0); break; default: printf("Unknown error from fmtmsg()0); } return 0; }

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 addseverity(3), perror(3)

2003-11-01 fmtmsg(3)