1GETPWNAM(3)                Linux Programmer's Manual               GETPWNAM(3)
2
3
4

NAME

6       getpwnam, getpwnam_r, getpwuid, getpwuid_r - get password file entry
7

SYNOPSIS

9       #include <sys/types.h>
10       #include <pwd.h>
11
12       struct passwd *getpwnam(const char *name);
13
14       struct passwd *getpwuid(uid_t uid);
15
16       int getpwnam_r(const char *name, struct passwd *pwd,
17                      char *buf, size_t buflen, struct passwd **result);
18
19       int getpwuid_r(uid_t uid, struct passwd *pwd,
20                      char *buf, size_t buflen, struct passwd **result);
21
22   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
23
24       getpwnam_r(), getpwuid_r():
25           _POSIX_C_SOURCE
26               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
27

DESCRIPTION

29       The getpwnam() function returns a pointer to a structure containing the
30       broken-out fields of the record in the password database (e.g., the lo‐
31       cal password file /etc/passwd, NIS, and LDAP) that matches the username
32       name.
33
34       The getpwuid() function returns a pointer to a structure containing the
35       broken-out  fields  of the record in the password database that matches
36       the user ID uid.
37
38       The passwd structure is defined in <pwd.h> as follows:
39
40           struct passwd {
41               char   *pw_name;       /* username */
42               char   *pw_passwd;     /* user password */
43               uid_t   pw_uid;        /* user ID */
44               gid_t   pw_gid;        /* group ID */
45               char   *pw_gecos;      /* user information */
46               char   *pw_dir;        /* home directory */
47               char   *pw_shell;      /* shell program */
48           };
49
50       See passwd(5) for more information about these fields.
51
52       The getpwnam_r() and getpwuid_r() functions obtain the same information
53       as  getpwnam() and getpwuid(), but store the retrieved passwd structure
54       in the space pointed to by pwd.  The string fields pointed  to  by  the
55       members  of  the  passwd structure are stored in the buffer buf of size
56       buflen.  A pointer to the result (in case of success) or NULL (in  case
57       no entry was found or an error occurred) is stored in *result.
58
59       The call
60
61           sysconf(_SC_GETPW_R_SIZE_MAX)
62
63       returns either -1, without changing errno, or an initial suggested size
64       for buf.  (If this size is too small, the call fails  with  ERANGE,  in
65       which case the caller can retry with a larger buffer.)
66

RETURN VALUE

68       The  getpwnam()  and  getpwuid() functions return a pointer to a passwd
69       structure, or NULL if the matching entry is not found or an  error  oc‐
70       curs.  If an error occurs, errno is set appropriately.  If one wants to
71       check errno after the call, it should be set to zero before the call.
72
73       The return value may point to a static area, and may be overwritten  by
74       subsequent  calls  to  getpwent(3), getpwnam(), or getpwuid().  (Do not
75       pass the returned pointer to free(3).)
76
77       On success, getpwnam_r() and getpwuid_r() return zero, and set  *result
78       to  pwd.  If no matching password record was found, these functions re‐
79       turn 0 and store NULL in *result.  In case of error, an error number is
80       returned, and NULL is stored in *result.
81

ERRORS

83       0 or ENOENT or ESRCH or EBADF or EPERM or ...
84              The given name or uid was not found.
85
86       EINTR  A signal was caught; see signal(7).
87
88       EIO    I/O error.
89
90       EMFILE The per-process limit on the number of open file descriptors has
91              been reached.
92
93       ENFILE The system-wide limit on the total number of open files has been
94              reached.
95
96       ENOMEM Insufficient memory to allocate passwd structure.
97
98       ERANGE Insufficient buffer space supplied.
99

FILES

101       /etc/passwd
102              local password database file
103

ATTRIBUTES

105       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
106       tributes(7).
107
108       ┌──────────────┬───────────────┬─────────────────────────────┐
109Interface     Attribute     Value                       
110       ├──────────────┼───────────────┼─────────────────────────────┤
111getpwnam()    │ Thread safety │ MT-Unsafe race:pwnam locale │
112       ├──────────────┼───────────────┼─────────────────────────────┤
113getpwuid()    │ Thread safety │ MT-Unsafe race:pwuid locale │
114       ├──────────────┼───────────────┼─────────────────────────────┤
115getpwnam_r(), │ Thread safety │ MT-Safe locale              │
116getpwuid_r()  │               │                             │
117       └──────────────┴───────────────┴─────────────────────────────┘

CONFORMING TO

119       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.  The pw_gecos  field  is  not
120       specified in POSIX, but is present on most implementations.
121

NOTES

123       The  formulation given above under "RETURN VALUE" is from POSIX.1-2001.
124       It does not call "not found" an error, and hence does not specify  what
125       value errno might have in this situation.  But that makes it impossible
126       to recognize errors.  One might argue that  according  to  POSIX  errno
127       should be left unchanged if an entry is not found.  Experiments on var‐
128       ious UNIX-like systems show that lots of different values occur in this
129       situation:  0,  ENOENT,  EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably
130       others.
131
132       The pw_dir field contains the name of the initial working directory  of
133       the user.  Login programs use the value of this field to initialize the
134       HOME environment variable for the login  shell.   An  application  that
135       wants  to  determine its user's home directory should inspect the value
136       of HOME (rather than the value getpwuid(getuid())->pw_dir)  since  this
137       allows the user to modify their notion of "the home directory" during a
138       login session.  To determine the (initial) home  directory  of  another
139       user, it is necessary to use getpwnam("username")->pw_dir or similar.
140

EXAMPLES

142       The program below demonstrates the use of getpwnam_r() to find the full
143       username and user ID for the username supplied as a command-line  argu‐
144       ment.
145
146       #include <pwd.h>
147       #include <stdint.h>
148       #include <stdio.h>
149       #include <stdlib.h>
150       #include <unistd.h>
151       #include <errno.h>
152
153       int
154       main(int argc, char *argv[])
155       {
156           struct passwd pwd;
157           struct passwd *result;
158           char *buf;
159           size_t bufsize;
160           int s;
161
162           if (argc != 2) {
163               fprintf(stderr, "Usage: %s username\n", argv[0]);
164               exit(EXIT_FAILURE);
165           }
166
167           bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
168           if (bufsize == -1)          /* Value was indeterminate */
169               bufsize = 16384;        /* Should be more than enough */
170
171           buf = malloc(bufsize);
172           if (buf == NULL) {
173               perror("malloc");
174               exit(EXIT_FAILURE);
175           }
176
177           s = getpwnam_r(argv[1], &pwd, buf, bufsize, &result);
178           if (result == NULL) {
179               if (s == 0)
180                   printf("Not found\n");
181               else {
182                   errno = s;
183                   perror("getpwnam_r");
184               }
185               exit(EXIT_FAILURE);
186           }
187
188           printf("Name: %s; UID: %jd\n", pwd.pw_gecos,
189                   (intmax_t) pwd.pw_uid);
190           exit(EXIT_SUCCESS);
191       }
192

SEE ALSO

194       endpwent(3),  fgetpwent(3),  getgrnam(3), getpw(3), getpwent(3), getsp‐
195       nam(3), putpwent(3), setpwent(3), passwd(5)
196

COLOPHON

198       This page is part of release 5.10 of the Linux  man-pages  project.   A
199       description  of  the project, information about reporting bugs, and the
200       latest    version    of    this    page,    can     be     found     at
201       https://www.kernel.org/doc/man-pages/.
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205GNU                               2020-11-01                       GETPWNAM(3)
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