1 .\" Copyright 1995 James R. Van Zandt <jrv@vanzandt.mv.com>
3 .\" %%%LICENSE_START(VERBATIM)
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25 .\" Changed Tue Sep 19 01:49:29 1995, aeb: moved from man2 to man3
26 .\" added ref to /etc/utmp, added BUGS section, etc.
27 .\" modified 2003 Walter Harms, aeb - added getlogin_r, note on stdin use
28 .TH GETLOGIN 3 2013-04-19 "GNU" "Linux Programmer's Manual"
30 getlogin, getlogin_r, cuserid \- get username
32 .B #include <unistd.h>
34 .B "char *getlogin(void);"
36 .BI "int getlogin_r(char *" buf ", size_t " bufsize );
40 .BI "char *cuserid(char *" string );
43 Feature Test Macro Requirements for glibc (see
44 .BR feature_test_macros (7)):
48 _REENTRANT || _POSIX_C_SOURCE\ >=\ 199506L
54 returns a pointer to a string containing the name of
55 the user logged in on the controlling terminal of the process, or a
56 null pointer if this information cannot be determined.
58 statically allocated and might be overwritten on subsequent calls to
63 returns this same username in the array
69 returns a pointer to a string containing a username
70 associated with the effective user ID of the process.
72 is not a null pointer, it should be an array that can hold at least
73 \fBL_cuserid\fP characters; the string is returned in this array.
74 Otherwise, a pointer to a string in a static area is returned.
76 string is statically allocated and might be overwritten on subsequent
77 calls to this function or to
80 The macro \fBL_cuserid\fP is an integer constant that indicates how
81 long an array you might need to store a username.
82 \fBL_cuserid\fP is declared in \fI<stdio.h>\fP.
84 These functions let your program identify positively the user who is
87 or the user who logged in this session
89 (These can differ when set-user-ID programs are involved.)
91 For most purposes, it is more useful to use the environment variable
92 \fBLOGNAME\fP to find out who the user is.
94 precisely because the user can set \fBLOGNAME\fP arbitrarily.
97 returns a pointer to the username when successful,
98 and NULL on failure, with
100 set to indicate the cause of the error.
102 returns 0 when successful, and nonzero on failure.
107 The calling process already has the maximum allowed number of open files.
110 The system already has the maximum allowed number of open files.
113 The calling process has no controlling terminal.
117 The length of the username, including the terminating null byte (\(aq\\0\(aq),
124 There was no corresponding entry in the utmp-file.
127 Insufficient memory to allocate passwd structure.
130 Standard input didn't refer to a terminal.
135 password database file
138 (traditionally \fI/etc/utmp\fP;
139 some libc versions used \fI/var/adm/utmp\fP)
141 .SS Multithreading (see pthreads(7))
144 function is not thread-safe.
148 function is thread-safe.
152 function is thread-safe with exceptions.
153 It is not thread-safe if called with a NULL parameter.
158 specified in POSIX.1-2001.
162 function which uses the real
163 user ID rather than the effective user ID.
167 was included in the 1988 version of POSIX,
168 but removed from the 1990 version.
169 It was present in SUSv2, but removed in POSIX.1-2001.
176 associated with a session, even if it has no controlling terminal.
178 Unfortunately, it is often rather easy to fool
180 Sometimes it does not work at all, because some program messed up
182 Often, it gives only the first 8 characters of
184 The user currently logged in on the controlling terminal
185 of our program need not be the user who started it.
188 for security-related purposes.
190 Note that glibc does not follow the POSIX specification and uses
195 (Other recent systems, like SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8
196 all return the login name also when
200 Nobody knows precisely what
202 does; avoid it in portable programs.
203 Or avoid it altogether: use
204 .I getpwuid(geteuid())