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
13 getpwnam, getpwnam_r — search user database for a name
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16 #include <pwd.h>
17 struct passwd *getpwnam(const char *name);
19 int getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
20 size_t bufsize, struct passwd **result);
21
23 The getpwnam() function shall search the user database for an entry
24 with a matching name.
25 The getpwnam() function need not be thread-safe.
27 Applications wishing to check for error situations should set errno to
29 0 before calling getpwnam(). If getpwnam() returns a null pointer and
30 errno is non-zero, an error occurred.
31 The getpwnam_r() function shall update the passwd structure pointed to
33 by pwd and store a pointer to that structure at the location pointed to
34 by result. The structure shall contain an entry from the user database
35 with a matching name. Storage referenced by the structure is allocated
36 from the memory provided with the buffer parameter, which is bufsize
37 bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX) returns either
38 −1 without changing errno or an initial value suggested for the size of
39 this buffer. A null pointer shall be returned at the location pointed
40 to by result on error or if the requested entry is not found.
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43 The getpwnam() function shall return a pointer to a struct passwd with
44 the structure as defined in <pwd.h> with a matching entry if found. A
45 null pointer shall be returned if the requested entry is not found, or
46 an error occurs. 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().
54 The getpwnam_r() function shall return zero on success or if the
56 requested entry was not found and no error has occurred. If an error
57 has occurred, an error number shall be returned to indicate the error.
58
60 These functions may fail if:
61 EIO An I/O error has occurred.
63 EINTR A signal was caught during getpwnam().
65 EMFILE All file descriptors available to the process are currently
67 open.
68 ENFILE The maximum allowable number of files is currently open in the
70 system.
71 The getpwnam_r() function may fail if:
73 ERANGE Insufficient storage was supplied via buffer and bufsize to con‐
75 tain the data to be referenced by the resulting passwd struc‐
76 ture.
77 The following sections are informative.
79
81 Note that sysconf(_SC_GETPW_R_SIZE_MAX) may return −1 if there is no
82 hard limit on the size of the buffer needed to store all the groups
83 returned. This example shows how an application can allocate a buffer
84 of sufficient size to work with getpwnam_r().
85 long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
87 size_t len;
88 if (initlen == −1)
89 /* Default initial length. */
90 len = 1024;
91 else
92 len = (size_t) initlen;
93 struct passwd result;
94 struct passwd *resultp;
95 char *buffer = malloc(len);
96 if (buffer == NULL)
97 ...handle error...
98 int e;
99 while ((e = getpwnam_r("someuser", &result, buffer, len, &resultp))
100 == ERANGE)
101 {
102 size_t newlen = 2 * len;
103 if (newlen < len)
104 ...handle error...
105 len = newlen;
106 char *newbuffer = realloc(buffer, len);
107 if (newbuffer == NULL)
108 ...handle error...
109 buffer = newbuffer;
110 }
111 if (e != 0)
112 ...handle error...
113 free (buffer);
114 Getting an Entry for the Login Name
116 The following example uses the getlogin() function to return the name
117 of the user who logged in; this information is passed to the getpwnam()
118 function to get the user database entry for that user.
119 #include <sys/types.h>
121 #include <pwd.h>
122 #include <unistd.h>
123 #include <stdio.h>
124 #include <stdlib.h>
125 ...
126 char *lgn;
127 struct passwd *pw;
128 ...
129 if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
130 fprintf(stderr, "Get of user information failed.\n"); exit(1);
131 }
132 ...
133
135 Three names associated with the current process can be determined: get‐
136 pwuid(geteuid()) returns the name associated with the effective user ID
137 of the process; getlogin() returns the name associated with the current
138 login activity; and getpwuid(getuid()) returns the name associated with
139 the real user ID of the process.
140 The getpwnam_r() function is thread-safe and returns values in a user-
142 supplied buffer instead of possibly using a static data area that may
143 be overwritten by each call.
144 Portable applications should take into account that it is usual for an
146 implementation to return −1 from sysconf() indicating that there is no
147 maximum for _SC_GETPW_R_SIZE_MAX.
148
150 None.
151
153 None.
154
156 getpwuid(), sysconf()
157 The Base Definitions volume of POSIX.1‐2008, <pwd.h>, <sys_types.h>
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161 Portions of this text are reprinted and reproduced in electronic form
162 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
163 -- Portable Operating System Interface (POSIX), The Open Group Base
164 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
165 cal and Electronics Engineers, Inc and The Open Group. (This is
166 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
167 event of any discrepancy between this version and the original IEEE and
168 The Open Group Standard, the original IEEE and The Open Group Standard
169 is the referee document. The original Standard can be obtained online
170 at http://www.unix.org/online.html .
171 Any typographical or formatting errors that appear in this page are
173 most likely to have been introduced during the conversion of the source
174 files to man page format. To report such errors, see https://www.ker‐
175 nel.org/doc/man-pages/reporting_bugs.html .
176IEEE/The Open Group 2013 GETPWNAM(3P)