1GETLOGIN(3P) POSIX Programmer's Manual GETLOGIN(3P)
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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 getlogin, getlogin_r — get login name
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16 #include <unistd.h>
17 char *getlogin(void);
19 int getlogin_r(char *name, size_t namesize);
20
22 The getlogin() function shall return a pointer to a string containing
23 the user name associated by the login activity with the controlling
24 terminal of the current process. If getlogin() returns a non-null
25 pointer, then that pointer points to the name that the user logged in
26 under, even if there are several login names with the same user ID.
27 The getlogin() function need not be thread-safe.
29 The getlogin_r() function shall put the name associated by the login
31 activity with the controlling terminal of the current process in the
32 character array pointed to by name. The array is namesize characters
33 long and should have space for the name and the terminating null char‐
34 acter. The maximum size of the login name is {LOGIN_NAME_MAX}.
35 If getlogin_r() is successful, name points to the name the user used at
37 login, even if there are several login names with the same user ID.
38 The getlogin() and getlogin_r() functions may make use of file descrip‐
40 tors 0, 1, and 2 to find the controlling terminal of the current
41 process, examining each in turn until the terminal is found. If in this
42 case none of these three file descriptors is open to the controlling
43 terminal, these functions may fail. The method used to find the termi‐
44 nal associated with a file descriptor may depend on the file descriptor
45 being open to the actual terminal device, not /dev/tty.
46
48 Upon successful completion, getlogin() shall return a pointer to the
49 login name or a null pointer if the user's login name cannot be found.
50 Otherwise, it shall return a null pointer and set errno to indicate the
51 error.
52 The application shall not modify the string returned. The returned
54 pointer might be invalidated or the string content might be overwritten
55 by a subsequent call to getlogin().
56 If successful, the getlogin_r() function shall return zero; otherwise,
58 an error number shall be returned to indicate the error.
59
61 These functions may fail if:
62 EMFILE All file descriptors available to the process are currently
64 open.
65 ENFILE The maximum allowable number of files is currently open in the
67 system.
68 ENOTTY None of the file descriptors 0, 1, or 2 is open to the control‐
70 ling terminal of the current process.
71 ENXIO The calling process has no controlling terminal.
73 The getlogin_r() function may fail if:
75 ERANGE The value of namesize is smaller than the length of the string
77 to be returned including the terminating null character.
78 The following sections are informative.
80
82 Getting the User Login Name S
83 The following example calls the getlogin() function to obtain the name
84 of the user associated with the calling process, and passes this infor‐
85 mation to the getpwnam() function to get the associated user database
86 information.
87 #include <unistd.h>
89 #include <sys/types.h>
90 #include <pwd.h>
91 #include <stdio.h>
92 ...
93 char *lgn;
94 struct passwd *pw;
95 ...
96 if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
97 fprintf(stderr, "Get of user information failed.\n"); exit(1);
98 }
99
101 Three names associated with the current process can be determined: get‐
102 pwuid(geteuid()) shall return the name associated with the effective
103 user ID of the process; getlogin() shall return the name associated
104 with the current login activity; and getpwuid(getuid()) shall return
105 the name associated with the real user ID of the process.
106 The getlogin_r() function is thread-safe and returns values in a user-
108 supplied buffer instead of possibly using a static data area that may
109 be overwritten by each call.
110
112 The getlogin() function returns a pointer to the user's login name. The
113 same user ID may be shared by several login names. If it is desired to
114 get the user database entry that is used during login, the result of
115 getlogin() should be used to provide the argument to the getpwnam()
116 function. (This might be used to determine the user's login shell, par‐
117 ticularly where a single user has multiple login shells with distinct
118 login names, but the same user ID.)
119 The information provided by the cuserid() function, which was origi‐
121 nally defined in the POSIX.1‐1988 standard and subsequently removed,
122 can be obtained by the following:
123 getpwuid(geteuid())
125 while the information provided by historical implementations of
127 cuserid() can be obtained by:
128 getpwuid(getuid())
130 The thread-safe version of this function places the user name in a
132 user-supplied buffer and returns a non-zero value if it fails. The non-
133 thread-safe version may return the name in a static data area that may
134 be overwritten by each call.
135
137 None.
138
140 getpwnam(), getpwuid(), geteuid(), getuid()
141 The Base Definitions volume of POSIX.1‐2008, <limits.h>, <unistd.h>
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145 Portions of this text are reprinted and reproduced in electronic form
146 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
147 -- Portable Operating System Interface (POSIX), The Open Group Base
148 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
149 cal and Electronics Engineers, Inc and The Open Group. (This is
150 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
151 event of any discrepancy between this version and the original IEEE and
152 The Open Group Standard, the original IEEE and The Open Group Standard
153 is the referee document. The original Standard can be obtained online
154 at http://www.unix.org/online.html .
155 Any typographical or formatting errors that appear in this page are
157 most likely to have been introduced during the conversion of the source
158 files to man page format. To report such errors, see https://www.ker‐
159 nel.org/doc/man-pages/reporting_bugs.html .
160IEEE/The Open Group 2013 GETLOGIN(3P)