man3/getpwnam.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
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  26 .\"
  27 .\" References consulted:
  28 .\"     Linux libc source code
  29 .\"     Lewine's "POSIX Programmer's Guide" (O'Reilly & Associates, 1991)
  30 .\"     386BSD man pages
  31 .\"
  32 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  33 .\" Modified 1996-05-27 by Martin Schulze (joey@linux.de)
  34 .\" Modified 2003-11-15 by aeb
  35 .\" 2008-11-07, mtk, Added an example program for getpwnam_r().
  36 .\"
  37 .TH GETPWNAM 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  38 .SH NAME
  39 getpwnam, getpwnam_r, getpwuid, getpwuid_r \- get password file entry
  40 .SH SYNOPSIS
  41 .nf
  42 .B #include <sys/types.h>
  43 .B #include <pwd.h>
  44 .PP
  45 .BI "struct passwd *getpwnam(const char *" name );
  46 .PP
  47 .BI "struct passwd *getpwuid(uid_t " uid );
  48 .PP
  49 .BI "int getpwnam_r(const char *" name ", struct passwd *" pwd ,
  50 .BI "               char *" buf ", size_t " buflen ", struct passwd **" result );
  51 .PP
  52 .BI "int getpwuid_r(uid_t " uid ", struct passwd *" pwd ,
  53 .BI "               char *" buf ", size_t " buflen ", struct passwd **" result );
  54 .fi
  55 .PP
  56 .in -4n
  57 Feature Test Macro Requirements for glibc (see
  58 .BR feature_test_macros (7)):
  59 .in
  60 .PP
  61 .ad l
  62 .BR getpwnam_r (),
  63 .BR getpwuid_r ():
  64 .RS 4
  65 _POSIX_C_SOURCE
  66     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  67 .RE
  68 .ad b
  69 .SH DESCRIPTION
  70 The
  71 .BR getpwnam ()
  72 function returns a pointer to a structure containing
  73 the broken-out fields of the record in the password database
  74 (e.g., the local password file
  75 .IR /etc/passwd ,
  76 NIS, and LDAP)
  77 that matches the username
  78 .IR name .
  79 .PP
  80 The
  81 .BR getpwuid ()
  82 function returns a pointer to a structure containing
  83 the broken-out fields of the record in the password database
  84 that matches the user ID
  85 .IR uid .
  86 .PP
  87 The \fIpasswd\fP structure is defined in \fI<pwd.h>\fP as follows:
  88 .PP
  89 .in +4n
  90 .EX
  91 struct passwd {
  92     char   *pw_name;       /* username */
  93     char   *pw_passwd;     /* user password */
  94     uid_t   pw_uid;        /* user ID */
  95     gid_t   pw_gid;        /* group ID */
  96     char   *pw_gecos;      /* user information */
  97     char   *pw_dir;        /* home directory */
  98     char   *pw_shell;      /* shell program */
  99 };
 100 .EE
 101 .in
 102 .PP
 103 See
 104 .BR passwd (5)
 105 for more information about these fields.
 106 .PP
 107 The
 108 .BR getpwnam_r ()
 109 and
 110 .BR getpwuid_r ()
 111 functions obtain the same information as
 112 .BR getpwnam ()
 113 and
 114 .BR getpwuid (),
 115 but store the retrieved
 116 .I passwd
 117 structure in the space pointed to by
 118 .IR pwd .
 119 The string fields pointed to by the members of the
 120 .I passwd
 121 structure are stored in the buffer
 122 .I buf
 123 of size
 124 .IR buflen .
 125 A pointer to the result (in case of success) or NULL (in case no entry
 126 was found or an error occurred) is stored in
 127 .IR *result .
 128 .PP
 129 The call
 130 .PP
 131     sysconf(_SC_GETPW_R_SIZE_MAX)
 132 .PP
 133 returns either \-1, without changing
 134 .IR errno ,
 135 or an initial suggested size for
 136 .IR buf .
 137 (If this size is too small,
 138 the call fails with
 139 .BR ERANGE ,
 140 in which case the caller can retry with a larger buffer.)
 141 .SH RETURN VALUE
 142 The
 143 .BR getpwnam ()
 144 and
 145 .BR getpwuid ()
 146 functions return a pointer to a
 147 .I passwd
 148 structure, or NULL if the matching entry is not found or
 149 an error occurs.
 150 If an error occurs,
 151 .I errno
 152 is set appropriately.
 153 If one wants to check
 154 .I errno
 155 after the call, it should be set to zero before the call.
 156 .PP
 157 The return value may point to a static area, and may be overwritten
 158 by subsequent calls to
 159 .BR getpwent (3),
 160 .BR getpwnam (),
 161 or
 162 .BR getpwuid ().
 163 (Do not pass the returned pointer to
 164 .BR free (3).)
 165 .PP
 166 On success,
 167 .BR getpwnam_r ()
 168 and
 169 .BR getpwuid_r ()
 170 return zero, and set
 171 .IR *result
 172 to
 173 .IR pwd .
 174 If no matching password record was found,
 175 these functions return 0 and store NULL in
 176 .IR *result .
 177 In case of error, an error number is returned, and NULL is stored in
 178 .IR *result .
 179 .SH ERRORS
 180 .TP
 181 .BR 0 " or " ENOENT " or " ESRCH " or " EBADF " or " EPERM " or ... "
 182 The given
 183 .I name
 184 or
 185 .I uid
 186 was not found.
 187 .TP
 188 .B EINTR
 189 A signal was caught; see
 190 .BR signal (7).
 191 .TP
 192 .B EIO
 193 I/O error.
 194 .TP
 195 .B EMFILE
 196 The per-process limit on the number of open file descriptors has been reached.
 197 .TP
 198 .B ENFILE
 199 The system-wide limit on the total number of open files has been reached.
 200 .TP
 201 .B ENOMEM
 202 .\" not in POSIX
 203 Insufficient memory to allocate
 204 .I passwd
 205 structure.
 206 .\" This structure is static, allocated 0 or 1 times. No memory leak. (libc45)
 207 .TP
 208 .B ERANGE
 209 Insufficient buffer space supplied.
 210 .SH FILES
 211 .TP
 212 .I /etc/passwd
 213 local password database file
 214 .SH ATTRIBUTES
 215 For an explanation of the terms used in this section, see
 216 .BR attributes (7).
 217 .TS
 218 allbox;
 219 lb lb lb
 220 l l l.
 221 Interface       Attribute       Value
 222 T{
 223 .BR getpwnam ()
 224 T}      Thread safety   MT-Unsafe race:pwnam locale
 225 T{
 226 .BR getpwuid ()
 227 T}      Thread safety   MT-Unsafe race:pwuid locale
 228 T{
 229 .BR getpwnam_r (),
 230 .br
 231 .BR getpwuid_r ()
 232 T}      Thread safety   MT-Safe locale
 233 .TE
 234 .SH CONFORMING TO
 235 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 236 The
 237 .I pw_gecos
 238 field is not specified in POSIX, but is present on most implementations.
 239 .SH NOTES
 240 The formulation given above under "RETURN VALUE" is from POSIX.1-2001.
 241 It does not call "not found" an error, and hence does not specify what value
 242 .I errno
 243 might have in this situation.
 244 But that makes it impossible to recognize
 245 errors.
 246 One might argue that according to POSIX
 247 .I errno
 248 should be left unchanged if an entry is not found.
 249 Experiments on various
 250 UNIX-like systems show that lots of different values occur in this
 251 situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably others.
 252 .\" more precisely:
 253 .\" AIX 5.1 - gives ESRCH
 254 .\" OSF1 4.0g - gives EWOULDBLOCK
 255 .\" libc, glibc up to version 2.6, Irix 6.5 - give ENOENT
 256 .\" glibc since version 2.7 - give 0
 257 .\" FreeBSD 4.8, OpenBSD 3.2, NetBSD 1.6 - give EPERM
 258 .\" SunOS 5.8 - gives EBADF
 259 .\" Tru64 5.1b, HP-UX-11i, SunOS 5.7 - give 0
 260 .PP
 261 The
 262 .I pw_dir
 263 field contains the name of the initial working directory of the user.
 264 Login programs use the value of this field to initialize the
 265 .B HOME
 266 environment variable for the login shell.
 267 An application that wants to determine its user's home directory
 268 should inspect the value of
 269 .B HOME
 270 (rather than the value
 271 .IR getpwuid(getuid())\->pw_dir )
 272 since this allows the user to modify their notion of
 273 "the home directory" during a login session.
 274 To determine the (initial) home directory of another user,
 275 it is necessary to use
 276 .I getpwnam("username")\->pw_dir
 277 or similar.
 278 .SH EXAMPLE
 279 The program below demonstrates the use of
 280 .BR getpwnam_r ()
 281 to find the full username and user ID for the username
 282 supplied as a command-line argument.
 283 .PP
 284 .EX
 285 #include <pwd.h>
 286 #include <stdio.h>
 287 #include <stdlib.h>
 288 #include <unistd.h>
 289 #include <errno.h>
 290
 291 int
 292 main(int argc, char *argv[])
 293 {
 294     struct passwd pwd;
 295     struct passwd *result;
 296     char *buf;
 297     size_t bufsize;
 298     int s;
 299
 300     if (argc != 2) {
 301         fprintf(stderr, "Usage: %s username\en", argv[0]);
 302         exit(EXIT_FAILURE);
 303     }
 304
 305     bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
 306     if (bufsize == \-1)          /* Value was indeterminate */
 307         bufsize = 16384;        /* Should be more than enough */
 308
 309     buf = malloc(bufsize);
 310     if (buf == NULL) {
 311         perror("malloc");
 312         exit(EXIT_FAILURE);
 313     }
 314
 315     s = getpwnam_r(argv[1], &pwd, buf, bufsize, &result);
 316     if (result == NULL) {
 317         if (s == 0)
 318             printf("Not found\en");
 319         else {
 320             errno = s;
 321             perror("getpwnam_r");
 322         }
 323         exit(EXIT_FAILURE);
 324     }
 325
 326     printf("Name: %s; UID: %ld\en", pwd.pw_gecos, (long) pwd.pw_uid);
 327     exit(EXIT_SUCCESS);
 328 }
 329 .EE
 330 .SH SEE ALSO
 331 .BR endpwent (3),
 332 .BR fgetpwent (3),
 333 .BR getgrnam (3),
 334 .BR getpw (3),
 335 .BR getpwent (3),
 336 .BR getspnam (3),
 337 .BR putpwent (3),
 338 .BR setpwent (3),
 339 .BR passwd (5)