1 GETLOGIN(3C) Standard C Library Functions GETLOGIN(3C)
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5 NAME
6 getlogin, getlogin_r - get login name
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8 SYNOPSIS
9 #include <unistd.h>
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11 char *getlogin(void);
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14 char *getlogin_r(char *name, int namelen);
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17 Standard conforming
18 cc [ flag ... ] file... -D_POSIX_PTHREAD_SEMANTICS [ library ... ]
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20 int getlogin_r(char *name, size_t namesize);
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23 DESCRIPTION
24 The getlogin() function returns a pointer to the login name as found in
25 /var/adm/utmpx. It can be used in conjunction with getpwnam(3C) to
26 locate the correct password file entry when the same user ID is shared
27 by several login names.
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30 The login name plus the terminating null byte can be up to 33
31 characters in length. Newly-compiled programs should use the
32 LOGIN_NAME_MAX symbol, defined in <limits.h>, to size the buffer.
33 Older programs that call getlogin() expect only the legacy 9-character
34 length. These automatically link to a version of the getlogin()
35 functions that truncates longer login names. It's also possible to
36 compile new programs that link to truncating versions of these
37 functions by defining __USE_LEGACY_LOGNAME__ in the compile
38 environment.
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41 Some older programs will correctly handle long login names returned by
42 the getlogin() function. For this case, the user compatibility library
43 /usr/lib/getloginx.so.1 redirects to a version of the getlogin()
44 function that returns the long name. This library should be added to
45 such an application at runtime using LD_PRELOAD.
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48 If getlogin() is called within a process that is not attached to a
49 terminal, it returns a null pointer. The correct procedure for
50 determining the login name is to call cuserid(3C), or to call
51 getlogin() and if it fails to call getpwuid(3C).
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54 The getlogin_r() function has the same functionality as getlogin()
55 except that the caller must supply a buffer name with length namelen to
56 store the result. The name buffer should be at least LOGIN_NAME_MAX
57 bytes in size (defined in <limits.h>). The POSIX version (see
58 standards(5)) of getlogin_r() takes a namesize parameter of type
59 size_t. If the size of the supplied buffer is less than the size of
60 LOGIN_NAME_MAX and the name, including the null terminator, does not
61 fit inside the buffer, than an error will be generated. Otherwise, the
62 buffer name will be updated with the login name.
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65 RETURN VALUES
66 Upon successful completion, getlogin() returns a pointer to the login
67 name or a null pointer if the user's login name cannot be found.
68 Otherwise it returns a null pointer and sets errno to indicate the
69 error.
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72 The standard-conforming getlogin_r() returns 0 if successful, or the
73 error number upon failure.
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75 ERRORS
76 The getlogin_r() function will fail if:
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78 ERANGE
79 The size of the buffer is smaller than the result to be
80 returned.
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83 EINVAL
84 And entry for the current user was not found in the
85 /var/adm/utmpx file.
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89 The getlogin() and getlogin_r() functions may fail if:
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91 EMFILE
92 There are {OPEN_MAX} file descriptors currently open in the
93 calling process.
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96 ENFILE
97 The maximum allowable number of files is currently open in
98 the system.
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101 ENXIO
102 The calling process has no controlling terminal.
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106 The getlogin_r() function may fail if:
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108 ERANGE
109 The size of the buffer is smaller than the result to be
110 returned.
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113 USAGE
114 The return value of getlogin() points to thread-specific data whose
115 content is overwritten on each call by the same thread.
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118 Three names associated with the current process can be determined:
119 getpwuid(geteuid()) returns the name associated with the effective user
120 ID of the process; getlogin() returns the name associated with the
121 current login activity; and getpwuid(getuid()) returns the name
122 associated with the real user ID of the process.
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124 FILES
125 /var/adm/utmpx
126 user access and administration information
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129 /usr/lib/getloginx.so.1
130 A compatibility library that returns long login names
131 to older applications.
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134 /usr/lib/64/getloginx.so.1
135 A 64-bit compatibility library to return long login
136 names.
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139 ATTRIBUTES
140 See attributes(5) for descriptions of the following attributes:
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145 +--------------------+-----------------+
146 | ATTRIBUTE TYPE | ATTRIBUTE VALUE |
147 +--------------------+-----------------+
148 |Interface Stability | Standard |
149 +--------------------+-----------------+
150 |MT-Level | See below. |
151 +--------------------+-----------------+
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153 SEE ALSO
154 geteuid(2), getuid(2), cuserid(3C), getgrnam(3C), getpwnam(3C),
155 getpwuid(3C), utmpx(4), attributes(5), standards(5)
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157 NOTES
158 When compiling multithreaded programs, see Intro(3).
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161 The getlogin() function is safe to use in multithreaded applications,
162 but is discouraged. The getlogin_r() function should be used instead.
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165 Solaris 2.4 and earlier releases provided a getlogin_r() as specified
166 in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface
167 as described above. Support for the Draft 6 interface is provided for
168 compatibility only and may not be supported in future releases. New
169 applications and libraries should use the standard-conforming
170 interface.
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174 March 15, 2014 GETLOGIN(3C)