This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The fmtmsg() function shall display messages in a specified format
instead of the traditional printf() function.
Based on a message's classification component, fmtmsg() shall write a
formatted message either to standard error, to the console, or to
A formatted message consists of up to five components as defined
below. The component classification is not part of a message
displayed to the user, but defines the source of the message and
directs the display of the formatted message.
Contains the sum of identifying values constructed from
the constants defined below. Any one identifier from a
subclass may be used in combination with a single
identifier from a different subclass. Two or more
identifiers from the same subclass should not be used
together, with the exception of identifiers from the
display subclass. (Both display subclass identifiers may
be used so that messages can be displayed to both
standard error and the system console.)
Identifies the source of the condition. Identifiers
are: MM_HARD (hardware), MM_SOFT (software), and
Message Source Subclassifications
Identifies the type of software in which the
problem is detected. Identifiers are: MM_APPL
(application), MM_UTIL (utility), and MM_OPSYS
Indicates where the message is to be displayed.
Identifiers are: MM_PRINT to display the message on
the standard error stream, MM_CONSOLE to display
the message on the system console. One or both
identifiers may be used.
Indicates whether the application can recover from
the condition. Identifiers are: MM_RECOVER
(recoverable) and MM_NRECOV (non-recoverable).
An additional identifier, MM_NULLMC, indicates that no
classification component is supplied for the message.
label Identifies the source of the message. The format is two
fields separated by a <colon>. The first field is up to
10 bytes, the second is up to 14 bytes.
severity Indicates the seriousness of the condition. Identifiers
for the levels of severity are:
MM_HALT Indicates that the application has
encountered a severe fault and is halting.
Produces the string "HALT".
MM_ERROR Indicates that the application has detected a
fault. Produces the string "ERROR".
MM_WARNING Indicates a condition that is out of the
ordinary, that might be a problem, and should
be watched. Produces the string "WARNING".
MM_INFO Provides information about a condition that
is not in error. Produces the string "INFO".
MM_NOSEV Indicates that no severity level is supplied
for the message.
text Describes the error condition that produced the message.
The character string is not limited to a specific size.
If the character string is empty, then the text produced
action Describes the first step to be taken in the error-
recovery process. The fmtmsg() function precedes the
action string with the prefix: "TOFIX:". The action
string is not limited to a specific size.
tag An identifier that references on-line documentation for
the message. Suggested usage is that tag includes the
label and a unique identifying number. A sample tag is
The MSGVERB environment variable (for message verbosity) shall
determine for fmtmsg() which message components it is to select when
writing messages to standard error. The value of MSGVERB shall be a
<colon>-separated list of optional keywords. Valid keywords are:
label, severity, text, action, and tag. If MSGVERB contains a keyword
for a component and the component's value is not the component's null
value, fmtmsg() shall include that component in the message when
writing the message to standard error. If MSGVERB does not include a
keyword for a message component, that component shall not be included
in the display of the message. The keywords may appear in any order.
If MSGVERB is not defined, if its value is the null string, if its
value is not of the correct format, or if it contains keywords other
than the valid ones listed above, fmtmsg() shall select all
MSGVERB shall determine which components are selected for display to
standard error. All message components shall be included in console
The fmtmsg() function shall return one of the following values:
MM_OK The function succeeded.
MM_NOTOK The function failed completely.
MM_NOMSG The function was unable to generate a message on standard
error, but otherwise succeeded.
MM_NOCON The function was unable to generate a console message,
but otherwise succeeded.
1. The following example of fmtmsg():
fmtmsg(MM_PRINT, "XSI:cat", MM_ERROR, "illegal option","refer to cat in user's reference manual", "XSI:cat:001")
produces a complete message in the specified message format:
XSI:cat: ERROR: illegal optionTO FIX: refer to cat in user's reference manual XSI:cat:001
2. When the environment variable MSGVERB is set as follows:
and Example 1 is used, fmtmsg() produces:
ERROR: illegal optionTO FIX: refer to cat in user's reference manual
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 FMTMSG(3P)