1GETPWNAM(3) Linux Programmer's Manual GETPWNAM(3)
2
6 getpwnam, getpwnam_r, getpwuid, getpwuid_r - get password file entry
7
9 #include <sys/types.h>
10 #include <pwd.h>
11 struct passwd *getpwnam(const char *name);
13 struct passwd *getpwuid(uid_t uid);
14 int getpwnam_r(const char *restrict name, struct passwd *restrict pwd,
16 char *restrict buf, size_t buflen,
17 struct passwd **restrict result);
18 int getpwuid_r(uid_t uid, struct passwd *restrict pwd,
19 char *restrict buf, size_t buflen,
20 struct passwd **restrict result);
21 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
23 getpwnam_r(), getpwuid_r():
25 _POSIX_C_SOURCE
26 || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
27
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 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 The passwd structure is defined in <pwd.h> as follows:
39 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 See passwd(5) for more information about these fields.
51 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 The call
60 sysconf(_SC_GETPW_R_SIZE_MAX)
62 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
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 to indicate the error. If one
71 wants to check errno after the call, it should be set to zero before
72 the call.
73 The return value may point to a static area, and may be overwritten by
75 subsequent calls to getpwent(3), getpwnam(), or getpwuid(). (Do not
76 pass the returned pointer to free(3).)
77 On success, getpwnam_r() and getpwuid_r() return zero, and set *result
79 to pwd. If no matching password record was found, these functions re‐
80 turn 0 and store NULL in *result. In case of error, an error number is
81 returned, and NULL is stored in *result.
82
84 0 or ENOENT or ESRCH or EBADF or EPERM or ...
85 The given name or uid was not found.
86 EINTR A signal was caught; see signal(7).
88 EIO I/O error.
90 EMFILE The per-process limit on the number of open file descriptors has
92 been reached.
93 ENFILE The system-wide limit on the total number of open files has been
95 reached.
96 ENOMEM Insufficient memory to allocate passwd structure.
98 ERANGE Insufficient buffer space supplied.
100
102 /etc/passwd
103 local password database file
104
106 For an explanation of the terms used in this section, see at‐
107 tributes(7).
108 ┌──────────────┬───────────────┬───────────────────────────────────────┐
110 │Interface │ Attribute │ Value │
111 ├──────────────┼───────────────┼───────────────────────────────────────┤
112 │getpwnam() │ Thread safety │ MT-Unsafe race:pwnam locale │
113 ├──────────────┼───────────────┼───────────────────────────────────────┤
114 │getpwuid() │ Thread safety │ MT-Unsafe race:pwuid locale │
115 ├──────────────┼───────────────┼───────────────────────────────────────┤
116 │getpwnam_r(), │ Thread safety │ MT-Safe locale │
117 │getpwuid_r() │ │ │
118 └──────────────┴───────────────┴───────────────────────────────────────┘
119
121 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. The pw_gecos field is not
122 specified in POSIX, but is present on most implementations.
123
125 The formulation given above under "RETURN VALUE" is from POSIX.1-2001.
126 It does not call "not found" an error, and hence does not specify what
127 value errno might have in this situation. But that makes it impossible
128 to recognize errors. One might argue that according to POSIX errno
129 should be left unchanged if an entry is not found. Experiments on var‐
130 ious UNIX-like systems show that lots of different values occur in this
131 situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably
132 others.
133 The pw_dir field contains the name of the initial working directory of
135 the user. Login programs use the value of this field to initialize the
136 HOME environment variable for the login shell. An application that
137 wants to determine its user's home directory should inspect the value
138 of HOME (rather than the value getpwuid(getuid())->pw_dir) since this
139 allows the user to modify their notion of "the home directory" during a
140 login session. To determine the (initial) home directory of another
141 user, it is necessary to use getpwnam("username")->pw_dir or similar.
142
144 The program below demonstrates the use of getpwnam_r() to find the full
145 username and user ID for the username supplied as a command-line argu‐
146 ment.
147 #include <pwd.h>
149 #include <stdint.h>
150 #include <stdio.h>
151 #include <stdlib.h>
152 #include <unistd.h>
153 #include <errno.h>
154 int
156 main(int argc, char *argv[])
157 {
158 struct passwd pwd;
159 struct passwd *result;
160 char *buf;
161 size_t bufsize;
162 int s;
163 if (argc != 2) {
165 fprintf(stderr, "Usage: %s username\n", argv[0]);
166 exit(EXIT_FAILURE);
167 }
168 bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
170 if (bufsize == -1) /* Value was indeterminate */
171 bufsize = 16384; /* Should be more than enough */
172 buf = malloc(bufsize);
174 if (buf == NULL) {
175 perror("malloc");
176 exit(EXIT_FAILURE);
177 }
178 s = getpwnam_r(argv[1], &pwd, buf, bufsize, &result);
180 if (result == NULL) {
181 if (s == 0)
182 printf("Not found\n");
183 else {
184 errno = s;
185 perror("getpwnam_r");
186 }
187 exit(EXIT_FAILURE);
188 }
189 printf("Name: %s; UID: %jd\n", pwd.pw_gecos,
191 (intmax_t) pwd.pw_uid);
192 exit(EXIT_SUCCESS);
193 }
194
196 endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3), getsp‐
197 nam(3), putpwent(3), setpwent(3), passwd(5)
198
200 This page is part of release 5.13 of the Linux man-pages project. A
201 description of the project, information about reporting bugs, and the
202 latest version of this page, can be found at
203 https://www.kernel.org/doc/man-pages/.
204GNU 2021-03-22 GETPWNAM(3)