1FMTMSG(3)                  Linux Programmer's Manual                 FMTMSG(3)
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NAME

6       fmtmsg - print formatted error messages
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SYNOPSIS

9       #include <fmtmsg.h>
10
11       int fmtmsg(long classification, const char *label,
12                  int severity, const char *text,
13                  const char *action, const char *tag);
14

DESCRIPTION

16       This  function  displays  a  message  described by its arguments on the
17       device(s) specified in the classification argument.  For messages writ‐
18       ten to stderr, the format depends on the MSGVERB environment variable.
19
20       The  label  argument  identifies the source of the message.  The string
21       must consist of two colon separated parts where the first part has  not
22       more than 10 and the second part not more than 14 characters.
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24       The text argument describes the condition of the error.
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26       The action argument describes possible steps to recover from the error.
27       If it is printed, it is prefixed by "TO FIX: ".
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29       The tag argument is a reference to the online documentation where  more
30       information  can  be  found.   It  should contain the label value and a
31       unique identification number.
32
33   Dummy arguments
34       Each of the arguments can have a dummy value.  The dummy classification
35       value  MM_NULLMC  (0L)  does  not  specify  any  output,  so nothing is
36       printed.  The dummy severity value NO_SEV (0) says that no severity  is
37       supplied.   The  values  MM_NULLLBL, MM_NULLTXT, MM_NULLACT, MM_NULLTAG
38       are synonyms for ((char *) 0), the empty string, and  MM_NULLSEV  is  a
39       synonym for NO_SEV.
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41   The classification argument
42       The  classification argument is the sum of values describing 4 types of
43       information.
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45       The first value defines the output channel.
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47       MM_PRINT    Output to stderr.
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49       MM_CONSOLE  Output to the system console.
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51       MM_PRINT | MM_CONSOLE
52                   Output to both.
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54       The second value is the source of the error:
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56       MM_HARD     A hardware error occurred.
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58       MM_FIRM     A firmware error occurred.
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60       MM_SOFT     A software error occurred.
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62       The third value encodes the detector of the problem:
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64       MM_APPL     It is detected by an application.
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66       MM_UTIL     It is detected by a utility.
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68       MM_OPSYS    It is detected by the operating system.
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70       The fourth value shows the severity of the incident:
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72       MM_RECOVER  It is a recoverable error.
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74       MM_NRECOV   It is a nonrecoverable error.
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76   The severity argument
77       The severity argument can take one of the following values:
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79       MM_NOSEV    No severity is printed.
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81       MM_HALT     This value is printed as HALT.
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83       MM_ERROR    This value is printed as ERROR.
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85       MM_WARNING  This value is printed as WARNING.
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87       MM_INFO     This value is printed as INFO.
88
89       The numeric values are between 0 and 4.  Using  addseverity(3)  or  the
90       environment  variable  SEV_LEVEL you can add more levels and strings to
91       print.
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RETURN VALUE

94       The function can return 4 values:
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96       MM_OK       Everything went smooth.
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98       MM_NOTOK    Complete failure.
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100       MM_NOMSG    Error writing to stderr.
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102       MM_NOCON    Error writing to the console.
103

ENVIRONMENT

105       The environment variable MSGVERB ("message verbosity") can be  used  to
106       suppress  parts of the output to stderr.  (It does not influence output
107       to the console.)  When this variable is defined, is non-NULL, and is  a
108       colon-separated list of valid keywords, then only the parts of the mes‐
109       sage corresponding to these keywords is printed.   Valid  keywords  are
110       "label", "severity", "text", "action" and "tag".
111
112       The  environment variable SEV_LEVEL can be used to introduce new sever‐
113       ity levels.  By default, only the five severity levels described  above
114       are available.  Any other numeric value would make fmtmsg() print noth‐
115       ing.  If the user puts SEV_LEVEL with a format like
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117              SEV_LEVEL=[description[:description[:...]]]
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119       in the environment of the process before the first  call  to  fmtmsg(),
120       where each description is of the form
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122              severity-keyword,level,printstring
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124       then  fmtmsg()  will also accept the indicated values for the level (in
125       addition to the standard levels 0–4), and use the indicated printstring
126       when such a level occurs.
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128       The  severity-keyword  part  is  not  used by fmtmsg() but it has to be
129       present.  The level part is a string representation of a  number.   The
130       numeric value must be a number greater than 4.  This value must be used
131       in the severity argument of fmtmsg() to select this class.  It  is  not
132       possible  to  overwrite any of the predefined classes.  The printstring
133       is the string printed when a message of  this  class  is  processed  by
134       fmtmsg().
135

VERSIONS

137       fmtmsg() is provided in glibc since version 2.1.
138

ATTRIBUTES

140       For   an   explanation   of   the  terms  used  in  this  section,  see
141       attributes(7).
142
143       ┌──────────┬───────────────┬─────────────────────────┐
144Interface Attribute     Value                   
145       ├──────────┼───────────────┼─────────────────────────┤
146fmtmsg()  │ Thread safety │ glibc >= 2.16: MT-Safe  │
147       │          │               │ glibc < 2.16: MT-Unsafe │
148       └──────────┴───────────────┴─────────────────────────┘
149       Before glibc 2.16, the fmtmsg() function uses a static variable that is
150       not protected, so it is not thread-safe.
151
152       Since  glibc  2.16,  the  fmtmsg()  function uses a lock to protect the
153       static variable, so it is thread-safe.
154

CONFORMING TO

156       The functions fmtmsg() and addseverity(3),  and  environment  variables
157       MSGVERB and SEV_LEVEL come from System V.
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159       The   function  fmtmsg()  and  the  environment  variable  MSGVERB  are
160       described in POSIX.1-2001 and POSIX.1-2008.
161

NOTES

163       System V and UnixWare man pages tell us that these functions have  been
164       replaced  by  "pfmt() and addsev()" or by "pfmt(), vpfmt(), lfmt(), and
165       vlfmt()", and will be removed later.
166

EXAMPLES

168       #include <stdio.h>
169       #include <stdlib.h>
170       #include <fmtmsg.h>
171
172       int
173       main(void)
174       {
175           long class = MM_PRINT | MM_SOFT | MM_OPSYS | MM_RECOVER;
176           int err;
177
178           err = fmtmsg(class, "util-linux:mount", MM_ERROR,
179                       "unknown mount option", "See mount(8).",
180                       "util-linux:mount:017");
181           switch (err) {
182           case MM_OK:
183               break;
184           case MM_NOTOK:
185               printf("Nothing printed\n");
186               break;
187           case MM_NOMSG:
188               printf("Nothing printed to stderr\n");
189               break;
190           case MM_NOCON:
191               printf("No console output\n");
192               break;
193           default:
194               printf("Unknown error from fmtmsg()\n");
195           }
196           exit(EXIT_SUCCESS);
197       }
198
199       The output should be:
200
201           util-linux:mount: ERROR: unknown mount option
202           TO FIX: See mount(8).  util-linux:mount:017
203
204       and after
205
206           MSGVERB=text:action; export MSGVERB
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208       the output becomes:
209
210           unknown mount option
211           TO FIX: See mount(8).
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SEE ALSO

214       addseverity(3), perror(3)
215

COLOPHON

217       This page is part of release 5.07 of the Linux  man-pages  project.   A
218       description  of  the project, information about reporting bugs, and the
219       latest    version    of    this    page,    can     be     found     at
220       https://www.kernel.org/doc/man-pages/.
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224                                  2020-06-09                         FMTMSG(3)
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