1GETPWNAM(3P) POSIX Programmer's Manual GETPWNAM(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 getpwnam, getpwnam_r — search user database for a name
13
15 #include <pwd.h>
16 struct passwd *getpwnam(const char *name);
18 int getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
19 size_t bufsize, struct passwd **result);
20
22 The getpwnam() function shall search the user database for an entry
23 with a matching name.
24 The getpwnam() function need not be thread-safe.
26 Applications wishing to check for error situations should set errno to
28 0 before calling getpwnam(). If getpwnam() returns a null pointer and
29 errno is non-zero, an error occurred.
30 The getpwnam_r() function shall update the passwd structure pointed to
32 by pwd and store a pointer to that structure at the location pointed to
33 by result. The structure shall contain an entry from the user database
34 with a matching name. Storage referenced by the structure is allocated
35 from the memory provided with the buffer parameter, which is bufsize
36 bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX) returns either
37 -1 without changing errno or an initial value suggested for the size of
38 this buffer. A null pointer shall be returned at the location pointed
39 to by result on error or if the requested entry is not found.
40
42 The getpwnam() function shall return a pointer to a struct passwd with
43 the structure as defined in <pwd.h> with a matching entry if found. A
44 null pointer shall be returned if the requested entry is not found, or
45 an error occurs. If the requested entry was not found, errno shall not
46 be changed. On error, errno shall be set to indicate the error.
47 The application shall not modify the structure to which the return
49 value points, nor any storage areas pointed to by pointers within the
50 structure. The returned pointer, and pointers within the structure,
51 might be invalidated or the structure or the storage areas might be
52 overwritten by a subsequent call to getpwent(), getpwnam(), or getp‐
53 wuid(). The returned pointer, and pointers within the structure, might
54 also be invalidated if the calling thread is terminated.
55 The getpwnam_r() function shall return zero on success or if the
57 requested entry was not found and no error has occurred. If an error
58 has occurred, an error number shall be returned to indicate the error.
59
61 These functions may fail if:
62 EIO An I/O error has occurred.
64 EINTR A signal was caught during getpwnam().
66 EMFILE All file descriptors available to the process are currently
68 open.
69 ENFILE The maximum allowable number of files is currently open in the
71 system.
72 The getpwnam_r() function may fail if:
74 ERANGE Insufficient storage was supplied via buffer and bufsize to con‐
76 tain the data to be referenced by the resulting passwd struc‐
77 ture.
78 The following sections are informative.
80
82 Note that sysconf(_SC_GETPW_R_SIZE_MAX) may return -1 if there is no
83 hard limit on the size of the buffer needed to store all the groups
84 returned. This example shows how an application can allocate a buffer
85 of sufficient size to work with getpwnam_r().
86 long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
89 size_t len;
90 if (initlen == -1)
91 /* Default initial length. */
92 len = 1024;
93 else
94 len = (size_t) initlen;
95 struct passwd result;
96 struct passwd *resultp;
97 char *buffer = malloc(len);
98 if (buffer == NULL)
99 ...handle error...
100 int e;
101 while ((e = getpwnam_r("someuser", &result, buffer, len, &resultp))
102 == ERANGE)
103 {
104 size_t newlen = 2 * len;
105 if (newlen < len)
106 ...handle error...
107 len = newlen;
108 char *newbuffer = realloc(buffer, len);
109 if (newbuffer == NULL)
110 ...handle error...
111 buffer = newbuffer;
112 }
113 if (e != 0)
114 ...handle error...
115 free (buffer);
116 Getting an Entry for the Login Name
118 The following example uses the getlogin() function to return the name
119 of the user who logged in; this information is passed to the getpwnam()
120 function to get the user database entry for that user.
121 #include <sys/types.h>
124 #include <pwd.h>
125 #include <unistd.h>
126 #include <stdio.h>
127 #include <stdlib.h>
128 ...
129 char *lgn;
130 struct passwd *pw;
131 ...
132 if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
133 fprintf(stderr, "Get of user information failed.\n"); exit(1);
134 }
135 ...
136
138 Three names associated with the current process can be determined: get‐
139 pwuid(geteuid()) returns the name associated with the effective user ID
140 of the process; getlogin() returns the name associated with the current
141 login activity; and getpwuid(getuid()) returns the name associated with
142 the real user ID of the process.
143 The getpwnam_r() function is thread-safe and returns values in a user-
145 supplied buffer instead of possibly using a static data area that may
146 be overwritten by each call.
147 Portable applications should take into account that it is usual for an
149 implementation to return -1 from sysconf() indicating that there is no
150 maximum for _SC_GETPW_R_SIZE_MAX.
151
153 None.
154
156 None.
157
159 getpwuid(), sysconf()
160 The Base Definitions volume of POSIX.1‐2017, <pwd.h>, <sys_types.h>
162
164 Portions of this text are reprinted and reproduced in electronic form
165 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
166 table Operating System Interface (POSIX), The Open Group Base Specifi‐
167 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
168 Electrical and Electronics Engineers, Inc and The Open Group. In the
169 event of any discrepancy between this version and the original IEEE and
170 The Open Group Standard, the original IEEE and The Open Group Standard
171 is the referee document. The original Standard can be obtained online
172 at http://www.opengroup.org/unix/online.html .
173 Any typographical or formatting errors that appear in this page are
175 most likely to have been introduced during the conversion of the source
176 files to man page format. To report such errors, see https://www.ker‐
177 nel.org/doc/man-pages/reporting_bugs.html .
178IEEE/The Open Group 2017 GETPWNAM(3P)