1GETPWUID(3P) POSIX Programmer's Manual GETPWUID(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 getpwuid, getpwuid_r — search user database for a user ID
13
15 #include <pwd.h>
16 struct passwd *getpwuid(uid_t uid);
18 int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
19 size_t bufsize, struct passwd **result);
20
22 The getpwuid() function shall search the user database for an entry
23 with a matching uid.
24 The getpwuid() function need not be thread-safe.
26 Applications wishing to check for error situations should set errno to
28 0 before calling getpwuid(). If getpwuid() returns a null pointer and
29 errno is set to non-zero, an error occurred.
30 The getpwuid_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 uid. 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 getpwuid() 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 If successful, the getpwuid_r() function shall return zero; otherwise,
57 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 getpwuid().
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 getpwuid_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.
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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 getpwuid_r().
85 long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
88 size_t len;
89 if (initlen == -1)
90 /* Default initial length. */
91 len = 1024;
92 else
93 len = (size_t) initlen;
94 struct passwd result;
95 struct passwd *resultp;
96 char *buffer = malloc(len);
97 if (buffer == NULL)
98 ...handle error...
99 int e;
100 while ((e = getpwuid_r(42, &result, buffer, len, &resultp)) == 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 Root User
116 The following example gets the user database entry for the user with
117 user ID 0 (root).
118 #include <sys/types.h>
121 #include <pwd.h>
122 ...
123 uid_t id = 0;
124 struct passwd *pwd;
125 pwd = getpwuid(id);
127 Finding the Name for the Effective User ID
129 The following example defines pws as a pointer to a structure of type
130 passwd, which is used to store the structure pointer returned by the
131 call to the getpwuid() function. The geteuid() function shall return
132 the effective user ID of the calling process; this is used as the
133 search criteria for the getpwuid() function. The call to getpwuid()
134 shall return a pointer to the structure containing that user ID value.
135 #include <unistd.h>
138 #include <sys/types.h>
139 #include <pwd.h>
140 ...
141 struct passwd *pws;
142 pws = getpwuid(geteuid());
143 Finding an Entry in the User Database
145 The following example uses getpwuid() to search the user database for a
146 user ID that was previously stored in a stat structure, then prints out
147 the user name if it is found. If the user is not found, the program
148 prints the numeric value of the user ID for the entry.
149 #include <sys/types.h>
152 #include <pwd.h>
153 #include <stdio.h>
154 ...
155 struct stat statbuf;
156 struct passwd *pwd;
157 ...
158 if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
159 printf(" %-8.8s", pwd->pw_name);
160 else
161 printf(" %-8d", statbuf.st_uid);
162
164 Three names associated with the current process can be determined: get‐
165 pwuid(geteuid()) returns the name associated with the effective user ID
166 of the process; getlogin() returns the name associated with the current
167 login activity; and getpwuid(getuid()) returns the name associated with
168 the real user ID of the process.
169 The getpwuid_r() function is thread-safe and returns values in a user-
171 supplied buffer instead of possibly using a static data area that may
172 be overwritten by each call.
173 Portable applications should take into account that it is usual for an
175 implementation to return -1 from sysconf() indicating that there is no
176 maximum for _SC_GETPW_R_SIZE_MAX.
177
179 None.
180
182 None.
183
185 getpwnam(), geteuid(), getuid(), getlogin(), sysconf()
186 The Base Definitions volume of POSIX.1‐2017, <pwd.h>, <sys_types.h>
188
190 Portions of this text are reprinted and reproduced in electronic form
191 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
192 table Operating System Interface (POSIX), The Open Group Base Specifi‐
193 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
194 Electrical and Electronics Engineers, Inc and The Open Group. In the
195 event of any discrepancy between this version and the original IEEE and
196 The Open Group Standard, the original IEEE and The Open Group Standard
197 is the referee document. The original Standard can be obtained online
198 at http://www.opengroup.org/unix/online.html .
199 Any typographical or formatting errors that appear in this page are
201 most likely to have been introduced during the conversion of the source
202 files to man page format. To report such errors, see https://www.ker‐
203 nel.org/doc/man-pages/reporting_bugs.html .
204IEEE/The Open Group 2017 GETPWUID(3P)