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   2 .\" Copyright (c) 2013 Gary Mills
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  13 .TH GETLOGIN 3C "May 25, 2013"
  14 .SH NAME
  15 getlogin, getlogin_r \- get login name
  16 .SH SYNOPSIS
  17 .LP
  18 .nf
  19 #include <unistd.h>
  20 
  21 \fBchar *\fR\fBgetlogin\fR(\fBvoid\fR);
  22 .fi
  23 
  24 .LP
  25 .nf
  26 \fBchar *\fR\fBgetlogin_r\fR(\fBchar *\fR\fIname\fR, \fBint\fR \fInamelen\fR);
  27 .fi
  28 
  29 .SS "Standard conforming"
  30 .LP
  31 .nf
  32 cc [ \fIflag \fR... ] \fIfile\fR... \fB-D_POSIX_PTHREAD_SEMANTICS\fR [ \fIlibrary \fR... ]
  33 
  34 \fBint\fR \fBgetlogin_r\fR(\fBchar *\fR\fIname\fR, \fBsize_t\fR \fInamesize\fR);
  35 .fi
  36 
  37 .SH DESCRIPTION
  38 .sp
  39 .LP
  40 The \fBgetlogin()\fR function returns a pointer to the login name as found in
  41 \fB/var/adm/utmpx\fR. It can be used in conjunction with \fBgetpwnam\fR(3C) to
  42 locate the correct password file entry when the same user \fBID\fR is shared by
  43 several login names.
  44 .sp
  45 .LP
  46 The login name plus the terminating null byte can be up to 33 characters
  47 in length.
  48 Newly-compiled programs should use the \fBLOGIN_NAME_MAX\fR symbol,
  49 defined in <\fBlimits.h\fR>, to size the buffer.
  50 Older programs that call \fBgetlogin()\fR  expect only the legacy
  51 9-character length.
  52 These automatically link to a version of the \fBgetlogin()\fR functions that
  53 truncates longer login names.
  54 It's also possible to compile new programs that link to truncating versions
  55 of these functions by defining \fB__USE_LEGACY_LOGNAME__\fR in the
  56 compile environment.
  57 .sp
  58 .LP
  59 Some older programs will correctly handle long login names returned
  60 by the \fBgetlogin()\fR function.
  61 For this case, the user compatibility library
  62 \fB/usr/lib/getloginx.so.1\fR redirects to a version of the \fBgetlogin()\fR
  63 function that returns the long name.
  64 This library should be added to such an application
  65 at runtime using \fBLD_PRELOAD\fR.
  66 .sp
  67 .LP
  68 If \fBgetlogin()\fR is called within a process that is not attached to a
  69 terminal, it returns a null pointer. The correct procedure for determining the
  70 login name is to call \fBcuserid\fR(3C), or to call \fBgetlogin()\fR and if it
  71 fails to call \fBgetpwuid\fR(3C).
  72 .sp
  73 .LP
  74 The \fBgetlogin_r()\fR function has the same functionality as \fBgetlogin()\fR
  75 except that the caller must supply a buffer \fIname\fR with length
  76 \fInamelen\fR to store the result.  The \fIname\fR buffer must be at least
  77 \fBLOGIN_NAME_MAX\fR bytes in size (defined in <\fBlimits.h\fR>). The
  78 POSIX version (see \fBstandards\fR(5)) of \fBgetlogin_r()\fR takes a
  79 \fInamesize\fR parameter of type \fBsize_t\fR.
  80 .SH RETURN VALUES
  81 .sp
  82 .LP
  83 Upon successful completion, \fBgetlogin()\fR returns a pointer to the login
  84 name or a null pointer if the user's login name cannot be found.  Otherwise it
  85 returns a null pointer and sets \fBerrno\fR to indicate the error.
  86 .sp
  87 .LP
  88 The standard-conforming \fBgetlogin_r()\fR returns \fB0\fR if successful, or
  89 the error number upon failure.
  90 .SH ERRORS
  91 .sp
  92 .LP
  93 The \fBgetlogin_r()\fR function will fail if:
  94 .sp
  95 .ne 2
  96 .na
  97 \fB\fBERANGE\fR\fR
  98 .ad
  99 .RS 10n
 100 The size of the buffer is smaller than the result to be returned.
 101 .RE
 102 
 103 .sp
 104 .ne 2
 105 .na
 106 \fB\fBEINVAL\fR\fR
 107 .ad
 108 .RS 10n
 109 And entry for the current user was not found in the \fB/var/adm/utmpx\fR file.
 110 .RE
 111 
 112 .sp
 113 .LP
 114 The \fBgetlogin()\fR and \fBgetlogin_r()\fR functions may fail if:
 115 .sp
 116 .ne 2
 117 .na
 118 \fB\fBEMFILE\fR\fR
 119 .ad
 120 .RS 10n
 121 There are {\fBOPEN_MAX\fR} file descriptors currently open in the calling
 122 process.
 123 .RE
 124 
 125 .sp
 126 .ne 2
 127 .na
 128 \fB\fBENFILE\fR\fR
 129 .ad
 130 .RS 10n
 131 The maximum allowable number of files is currently open in the system.
 132 .RE
 133 
 134 .sp
 135 .ne 2
 136 .na
 137 \fB\fBENXIO\fR\fR
 138 .ad
 139 .RS 10n
 140 The calling process has no controlling terminal.
 141 .RE
 142 
 143 .sp
 144 .LP
 145 The \fBgetlogin_r()\fR function may fail if:
 146 .sp
 147 .ne 2
 148 .na
 149 \fB\fBERANGE\fR\fR
 150 .ad
 151 .RS 10n
 152 The size of the buffer is smaller than the result to be returned.
 153 .RE
 154 
 155 .SH USAGE
 156 .sp
 157 .LP
 158 The return value of \fBgetlogin()\fR points to thread-specific data whose
 159 content is overwritten on each call by the same thread.
 160 .sp
 161 .LP
 162 Three names associated with the current process can be determined:
 163 \fBgetpwuid(\fR\fBgeteuid()\fR\fB)\fR returns the name associated with the
 164 effective user ID of the process; \fBgetlogin()\fR returns the name associated
 165 with the current login activity; and \fBgetpwuid(\fR\fBgetuid()\fR\fB)\fR
 166 returns the name associated with the real user ID of the process.
 167 .SH FILES
 168 .sp
 169 .ne 2
 170 .na
 171 \fB\fB/var/adm/utmpx\fR\fR
 172 .ad
 173 .RS 18n
 174 user access and administration information
 175 .RE
 176 
 177 .sp
 178 .ne 2
 179 .na
 180 \fB\fB/usr/lib/getloginx.so.1\fR\fR
 181 .ad
 182 .RS 18n
 183 A compatibility library that returns long login names to older applications.
 184 .RE
 185 
 186 .sp
 187 .ne 2
 188 .na
 189 \fB\fB/usr/lib/64/getloginx.so.1\fR\fR
 190 .ad
 191 .RS 18n
 192 A 64-bit compatibility library to return long login names.
 193 .RE
 194 
 195 .SH ATTRIBUTES
 196 .sp
 197 .LP
 198 See \fBattributes\fR(5) for descriptions of the following attributes:
 199 .sp
 200 
 201 .sp
 202 .TS
 203 box;
 204 c | c
 205 l | l .
 206 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 207 _
 208 Interface Stability     Standard
 209 _
 210 MT-Level        See below.
 211 .TE
 212 
 213 .SH SEE ALSO
 214 .sp
 215 .LP
 216 \fBgeteuid\fR(2), \fBgetuid\fR(2), \fBcuserid\fR(3C), \fBgetgrnam\fR(3C),
 217 \fBgetpwnam\fR(3C), \fBgetpwuid\fR(3C), \fButmpx\fR(4), \fBattributes\fR(5),
 218 \fBstandards\fR(5)
 219 .SH NOTES
 220 .sp
 221 .LP
 222 When compiling multithreaded programs, see \fBIntro\fR(3).
 223 .sp
 224 .LP
 225 The \fBgetlogin()\fR function is safe to use in multithreaded applications, but
 226 is discouraged. The \fBgetlogin_r()\fR function should be used instead.
 227 .sp
 228 .LP
 229 Solaris 2.4 and earlier releases provided a \fBgetlogin_r()\fR as specified in
 230 POSIX.1c Draft 6. The final POSIX.1c standard changed the interface as
 231 described above. Support for the Draft 6 interface is provided for
 232 compatibility only and may not be supported in future releases. New
 233 applications and libraries should use the standard-conforming interface.