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361763ff | 1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
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2 | .\" |
3 | .\" Copyright 1995 James R. Van Zandt <jrv@vanzandt.mv.com> | |
4 | .\" | |
5 | .\" Permission is granted to make and distribute verbatim copies of this | |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
c13182ef | 13 | .\" |
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14 | .\" Since the Linux kernel and libraries are constantly changing, this |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. The author(s) may not | |
18 | .\" have taken the same level of care in the production of this manual, | |
19 | .\" which is licensed free of charge, as they might when working | |
20 | .\" professionally. | |
c13182ef | 21 | .\" |
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22 | .\" Formatted or processed versions of this manual, if unaccompanied by |
23 | .\" the source, must acknowledge the copyright and authors of this work. | |
24 | .\" | |
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 | |
76492ece | 28 | .TH GETLOGIN 3 2008-06-29 "GNU" "Linux Programmer's Manual" |
fea681da | 29 | .SH NAME |
18701562 | 30 | getlogin, getlogin_r, cuserid \- get username |
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31 | .SH SYNOPSIS |
32 | .B #include <unistd.h> | |
33 | .sp | |
34 | .B "char *getlogin(void);" | |
35 | .br | |
36 | .BI "int getlogin_r(char *" buf ", size_t " bufsize ); | |
37 | .sp | |
38 | .B #include <stdio.h> | |
39 | .sp | |
40 | .BI "char *cuserid(char *" string ); | |
cc4615cc MK |
41 | .sp |
42 | .in -4n | |
43 | Feature Test Macro Requirements for glibc (see | |
44 | .BR feature_test_macros (7)): | |
45 | .in | |
46 | .sp | |
47 | .BR getlogin_r (): | |
e0bf9127 | 48 | _REENTRANT || _POSIX_C_SOURCE\ >=\ 199506L |
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49 | .br |
50 | .BR cuserid (): | |
51 | _XOPEN_SOURCE | |
fea681da | 52 | .SH DESCRIPTION |
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53 | .BR getlogin () |
54 | returns a pointer to a string containing the name of | |
fea681da | 55 | the user logged in on the controlling terminal of the process, or a |
ad3fd4c0 | 56 | NULL pointer if this information cannot be determined. |
c13182ef | 57 | The string is |
fea681da | 58 | statically allocated and might be overwritten on subsequent calls to |
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59 | this function or to |
60 | .BR cuserid (). | |
fea681da | 61 | .PP |
60a90ecd | 62 | .BR getlogin_r () |
18701562 | 63 | returns this same username in the array |
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64 | .I buf |
65 | of size | |
66 | .IR bufsize . | |
67 | .PP | |
60a90ecd | 68 | .BR cuserid () |
18701562 | 69 | returns a pointer to a string containing a username |
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70 | associated with the effective user ID of the process. |
71 | If \fIstring\fP | |
ad3fd4c0 | 72 | is not a NULL pointer, it should be an array that can hold at least |
fea681da | 73 | \fBL_cuserid\fP characters; the string is returned in this array. |
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74 | Otherwise, a pointer to a string in a static area is returned. |
75 | This | |
fea681da | 76 | string is statically allocated and might be overwritten on subsequent |
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77 | calls to this function or to |
78 | .BR getlogin (). | |
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79 | .PP |
80 | The macro \fBL_cuserid\fP is an integer constant that indicates how | |
18701562 | 81 | long an array you might need to store a username. |
1608e0bd | 82 | \fBL_cuserid\fP is declared in \fI<stdio.h>\fP. |
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83 | .PP |
84 | These functions let your program identify positively the user who is | |
988db661 | 85 | running |
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86 | .RB ( cuserid ()) |
87 | or the user who logged in this session | |
88 | .RB ( getlogin ()). | |
89 | (These can differ when set-user-ID programs are involved.) | |
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90 | .PP |
91 | For most purposes, it is more useful to use the environment variable | |
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92 | \fBLOGNAME\fP to find out who the user is. |
93 | This is more flexible | |
fea681da | 94 | precisely because the user can set \fBLOGNAME\fP arbitrarily. |
47297adb | 95 | .SH RETURN VALUE |
60a90ecd | 96 | .BR getlogin () |
18701562 | 97 | returns a pointer to the username when successful, |
fea681da | 98 | and NULL on failure. |
60a90ecd | 99 | .BR getlogin_r () |
c7094399 | 100 | returns 0 when successful, and nonzero on failure. |
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101 | .SH ERRORS |
102 | POSIX specifies | |
103 | .TP | |
104 | .B EMFILE | |
105 | The calling process already has the maximum allowed number of open files. | |
106 | .TP | |
107 | .B ENFILE | |
108 | The system already has the maximum allowed number of open files. | |
109 | .TP | |
110 | .B ENXIO | |
1285ff3d | 111 | The calling process has no controlling terminal. |
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112 | .TP |
113 | .B ERANGE | |
114 | (getlogin_r) | |
18701562 | 115 | The length of the username, including the terminating null byte, |
28d88c17 | 116 | is larger than |
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117 | .IR bufsize . |
118 | .LP | |
119 | Linux/glibc also has | |
120 | .TP | |
121 | .B ENOENT | |
122 | There was no corresponding entry in the utmp-file. | |
123 | .TP | |
124 | .B ENOMEM | |
125 | Insufficient memory to allocate passwd structure. | |
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126 | .TP |
127 | .B ENOTTY | |
128 | Standard input didn't refer to a terminal. | |
129 | (See BUGS.) | |
fea681da | 130 | .SH FILES |
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131 | .TP |
132 | \fI/etc/passwd\fP | |
133 | password database file | |
134 | .TP | |
135 | \fI/var/run/utmp\fP | |
136 | (traditionally \fI/etc/utmp\fP; | |
137 | some libc versions used \fI/var/adm/utmp\fP) | |
47297adb | 138 | .SH CONFORMING TO |
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139 | .BR getlogin () |
140 | and | |
141 | .BR getlogin_r () | |
142 | specified in POSIX.1-2001. | |
143 | ||
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144 | System V has a |
145 | .BR cuserid () | |
146 | function which uses the real | |
c13182ef | 147 | user ID rather than the effective user ID. |
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148 | The |
149 | .BR cuserid () | |
150 | function | |
c13182ef | 151 | was included in the 1988 version of POSIX, |
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152 | but removed from the 1990 version. |
153 | It was present in SUSv2, but removed in POSIX.1-2001. | |
fea681da | 154 | .LP |
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155 | OpenBSD has |
156 | .BR getlogin () | |
157 | and | |
158 | .BR setlogin (), | |
159 | and a username | |
1285ff3d | 160 | associated with a session, even if it has no controlling terminal. |
fea681da | 161 | .SH BUGS |
c13182ef | 162 | Unfortunately, it is often rather easy to fool |
b5cc2ffb | 163 | .BR getlogin (). |
fea681da | 164 | Sometimes it does not work at all, because some program messed up |
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165 | the utmp file. |
166 | Often, it gives only the first 8 characters of | |
167 | the login name. | |
1285ff3d | 168 | The user currently logged in on the controlling terminal |
fea681da | 169 | of our program need not be the user who started it. |
c13182ef | 170 | Avoid |
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171 | .BR getlogin () |
172 | for security-related purposes. | |
fea681da | 173 | .LP |
a306ffff | 174 | Note that glibc does not follow the POSIX specification and uses |
68e1685c | 175 | .I stdin |
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176 | instead of |
177 | .IR /dev/tty . | |
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178 | A bug. |
179 | (Other recent systems, like SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8 | |
180 | all return the login name also when | |
181 | .I stdin | |
68e1685c | 182 | is redirected.) |
fea681da | 183 | .LP |
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184 | Nobody knows precisely what |
185 | .BR cuserid () | |
b5cc2ffb | 186 | does; avoid it in portable programs. |
c13182ef | 187 | Or avoid it altogether: use |
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188 | .I getpwuid(geteuid()) |
189 | instead, if that is | |
fea681da | 190 | what you meant. |
4bd8c614 | 191 | .B Do not use |
b5cc2ffb | 192 | .BR cuserid (). |
47297adb | 193 | .SH SEE ALSO |
fea681da | 194 | .BR geteuid (2), |
1bced40f MK |
195 | .BR getuid (2), |
196 | .BR utmp (5) |