man3/getutent.3

   1 .\" Copyright 1995 Mark D. Roth (roth@uiuc.edu)
   2 .\"
   3 .\" This is free documentation; you can redistribute it and/or
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  22 .\" References consulted:
  23 .\"     Linux libc source code
  24 .\"     Solaris manpages
  25 .\"
  26 .\" Modified Thu Jul 25 14:43:46 MET DST 1996 by Michael Haardt
  27 .\"     <michael@cantor.informatik.rwth-aachen.de>
  28 .\"
  29 .TH GETUTENT 3 2008-06-29 "" "Linux Programmer's Manual"
  30 .SH NAME
  31 getutent, getutid, getutline, pututline, setutent, endutent,
  32 utmpname \- access utmp file entries
  33 .SH SYNOPSIS
  34 .B #include <utmp.h>
  35 .sp
  36 .B struct utmp *getutent(void);
  37 .br
  38 .BI "struct utmp *getutid(struct utmp *" ut );
  39 .br
  40 .BI "struct utmp *getutline(struct utmp *" ut );
  41 .sp
  42 .BI "struct utmp *pututline(struct utmp *" ut );
  43 .sp
  44 .B void setutent(void);
  45 .br
  46 .B void endutent(void);
  47 .sp
  48 .BI "int utmpname(const char *" file );
  49 .SH DESCRIPTION
  50 New applications should use the POSIX.1-specified "utmpx" versions of
  51 these functions; see CONFORMING TO.
  52
  53 .BR utmpname ()
  54 sets the name of the utmp-format file for the other utmp
  55 functions to access.
  56 If
  57 .BR utmpname ()
  58 is not used to set the filename
  59 before the other functions are used, they assume \fB_PATH_UTMP\fP, as
  60 defined in \fI<paths.h>\fP.
  61 .PP
  62 .BR setutent ()
  63 rewinds the file pointer to the beginning of the utmp file.
  64 It is generally a good idea to call it before any of the other
  65 functions.
  66 .PP
  67 .BR endutent ()
  68 closes the utmp file.
  69 It should be called when the user
  70 code is done accessing the file with the other functions.
  71 .PP
  72 .BR getutent ()
  73 reads a line from the current file position in the utmp file.
  74 It returns a pointer to a structure containing the fields of
  75 the line.
  76 The definition of this structure is shown in
  77 .BR utmp (5).
  78 .PP
  79 .BR getutid ()
  80 searches forward from the current file position in the utmp
  81 file based upon \fIut\fP.
  82 If \fIut\->ut_type\fP is one of \fBRUN_LVL\fP,
  83 \fBBOOT_TIME\fP, \fBNEW_TIME\fP, or \fBOLD_TIME\fP,
  84 .BR getutid ()
  85 will
  86 find the first entry whose \fIut_type\fP field matches \fIut\->ut_type\fP.
  87 If \fIut\->ut_type\fP is one of \fBINIT_PROCESS\fP, \fBLOGIN_PROCESS\fP,
  88 \fBUSER_PROCESS\fP, or \fBDEAD_PROCESS\fP,
  89 .BR getutid ()
  90 will find the
  91 first entry whose
  92 .I ut_id
  93 field matches \fIut\->ut_id\fP.
  94 .PP
  95 .BR getutline ()
  96 searches forward from the current file position in the utmp file.
  97 It scans entries whose
  98 .I ut_type
  99 is \fBUSER_PROCESS\fP
 100 or \fBLOGIN_PROCESS\fP and returns the first one whose
 101 .I ut_line
 102 field
 103 matches \fIut\->ut_line\fP.
 104 .PP
 105 .BR pututline ()
 106 writes the
 107 .I utmp
 108 structure \fIut\fP into the utmp file.
 109 It uses
 110 .BR getutid ()
 111 to search for the proper place in the file to insert
 112 the new entry.
 113 If it cannot find an appropriate slot for \fIut\fP,
 114 .BR pututline ()
 115 will append the new entry to the end of the file.
 116 .SH RETURN VALUE
 117 .BR getutent (),
 118 .BR getutid (),
 119 and
 120 .BR getutline ()
 121 return a pointer to a \fIstruct utmp\fP on success,
 122 and NULL on failure (which includes the "record not found" case).
 123 This \fIstruct utmp\fP is allocated in static storage, and may be
 124 overwritten by subsequent calls.
 125
 126 On success
 127 .BR pututline ()
 128 returns
 129 .IR ut ;
 130 on failure, it returns NULL.
 131
 132 .BR utmpname ()
 133 returns 0 if the new name was successfully stored, or \-1 on failure.
 134 .SH ERRORS
 135 .TP
 136 .B ENOMEM
 137 Out of memory.
 138 .TP
 139 .B ESRCH
 140 Record not found.
 141 .PP
 142 .BR setutent (),
 143 .BR pututline (),
 144 and the
 145 .B getut* ()
 146 functions can also fail for the reasons described in
 147 .BR open (2).
 148 .SH FILES
 149 /var/run/utmp   database of currently logged-in users
 150 .br
 151 /var/log/wtmp   database of past user logins
 152 .SH CONFORMING TO
 153 XPG2, SVr4.
 154 .LP
 155 In XPG2 and SVID 2 the function
 156 .BR pututline ()
 157 is documented to return void, and that is what it does on many systems
 158 (AIX, HP-UX, Linux libc5).
 159 HP-UX introduces a new function
 160 .BR _pututline ()
 161 with the prototype given above for
 162 .BR pututline ()
 163 (also found in Linux libc5).
 164 .LP
 165 All these functions are obsolete now on non-Linux systems.
 166 POSIX.1-2001, following SUSv1,
 167 does not have any of these functions, but instead uses
 168 .sp
 169 .B #include <utmpx.h>
 170 .sp
 171 .B struct utmpx *getutxent(void);
 172 .br
 173 .B struct utmpx *getutxid(const struct utmpx *);
 174 .br
 175 .B struct utmpx *getutxline(const struct utmpx *);
 176 .br
 177 .B struct utmpx *pututxline(const struct utmpx *);
 178 .br
 179 .B void setutxent(void);
 180 .br
 181 .B void endutxent(void);
 182 .PP
 183 These functions are provided by glibc,
 184 and perform the same task as their equivalents without the "x", but use
 185 .IR "struct utmpx" ,
 186 defined on Linux to be the same as
 187 .IR "struct utmp" .
 188 For completeness, glibc also provides
 189 .BR utmpxname (),
 190 although this function is not specified by POSIX.1.
 191 .PP
 192 On some other systems,
 193 the \fIutmpx\fP structure is a superset of the \fIutmp\fP structure,
 194 with additional fields, and larger versions of the existing fields,
 195 and parallel files are maintained, often
 196 .I /var/*/utmpx
 197 and
 198 .IR /var/*/wtmpx .
 199 .LP
 200 Linux glibc on the other hand does not use a parallel \fIutmpx\fP file
 201 since its \fIutmp\fP structure is already large enough.
 202 The "x" functions listed above are just aliases for
 203 their counterparts without the "x" (e.g.,
 204 .BR getutxent ()
 205 is an alias for
 206 .BR getutent ()).
 207 .SH NOTES
 208 .SS Glibc notes
 209 The above functions are not thread-safe.
 210 Glibc adds reentrant versions
 211 .sp
 212 .nf
 213 .BR "#define _GNU_SOURCE" "    /* or _SVID_SOURCE or _BSD_SOURCE;
 214 .RB "\&                          see " feature_test_macros "(7) */"
 215 .B #include <utmp.h>
 216 .sp
 217 .BI "int getutent_r(struct utmp *" ubuf ", struct utmp **" ubufp );
 218 .sp
 219 .BI "int getutid_r(struct utmp *" ut ,
 220 .BI "              struct utmp *" ubuf ", struct utmp **" ubufp );
 221 .sp
 222 .BI "int getutline_r(struct utmp *" ut ,
 223 .BI "                struct utmp *" ubuf ", struct utmp **" ubufp );
 224 .fi
 225 .sp
 226 These functions are GNU extensions, analogs of the functions of the
 227 same name without the _r suffix.
 228 The
 229 .I ubuf
 230 argument gives these functions a place to store their result.
 231 On success they return 0, and a pointer to the result is written in
 232 .IR *ubufp .
 233 On error these functions return \-1.
 234 There are no utmpx equivalents of the above functions.
 235 (POSIX.1 does not specify such functions.)
 236 .SH EXAMPLE
 237 The following example adds and removes a utmp record, assuming it is run
 238 from within a pseudo terminal.
 239 For usage in a real application, you
 240 should check the return values of
 241 .BR getpwuid (3)
 242 and
 243 .BR ttyname (3).
 244 .PP
 245 .nf
 246 #include <string.h>
 247 #include <stdlib.h>
 248 #include <pwd.h>
 249 #include <unistd.h>
 250 #include <utmp.h>
 251
 252 int
 253 main(int argc, char *argv[])
 254 {
 255     struct utmp entry;
 256
 257     system("echo before adding entry:;who");
 258
 259     entry.ut_type = USER_PROCESS;
 260     entry.ut_pid = getpid();
 261     strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
 262     /* only correct for ptys named /dev/tty[pqr][0\-9a\-z] */
 263     strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
 264     time(&entry.ut_time);
 265     strcpy(entry.ut_user, getpwuid(getuid())\->pw_name);
 266     memset(entry.ut_host, 0, UT_HOSTSIZE);
 267     entry.ut_addr = 0;
 268     setutent();
 269     pututline(&entry);
 270
 271     system("echo after adding entry:;who");
 272
 273     entry.ut_type = DEAD_PROCESS;
 274     memset(entry.ut_line, 0, UT_LINESIZE);
 275     entry.ut_time = 0;
 276     memset(entry.ut_user, 0, UT_NAMESIZE);
 277     setutent();
 278     pututline(&entry);
 279
 280     system("echo after removing entry:;who");
 281
 282     endutent();
 283     exit(EXIT_SUCCESS);
 284 }
 285 .fi
 286 .SH SEE ALSO
 287 .BR getutmp (3),
 288 .BR utmp (5)