1GETLOGIN(3)                Linux Programmer's Manual               GETLOGIN(3)
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NAME

6       getlogin, getlogin_r, cuserid - get username
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SYNOPSIS

9       #include <unistd.h>
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11       char *getlogin(void);
12       int getlogin_r(char *buf, size_t bufsize);
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14       #include <stdio.h>
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16       char *cuserid(char *string);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       getlogin_r(): _POSIX_C_SOURCE >= 199506L
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22       cuserid():
23           Since glibc 2.24:
24               (_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
25               || _GNU_SOURCE
26           Up to and including glibc 2.23:
27               _XOPEN_SOURCE
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DESCRIPTION

30       getlogin()  returns  a  pointer  to a string containing the name of the
31       user logged in on the controlling terminal of the process,  or  a  null
32       pointer if this information cannot be determined.  The string is stati‐
33       cally allocated and might be overwritten on subsequent  calls  to  this
34       function or to cuserid().
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36       getlogin_r()  returns  this same username in the array buf of size buf‐
37       size.
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39       cuserid() returns a pointer to a string containing a  username  associ‐
40       ated  with  the  effective  user ID of the process.  If string is not a
41       null pointer, it should be an array that can hold  at  least  L_cuserid
42       characters; the string is returned in this array.  Otherwise, a pointer
43       to a string in a static area is returned.  This  string  is  statically
44       allocated and might be overwritten on subsequent calls to this function
45       or to getlogin().
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47       The macro L_cuserid is an integer constant that indicates how  long  an
48       array  you  might  need  to store a username.  L_cuserid is declared in
49       <stdio.h>.
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51       These functions let your program identify positively the  user  who  is
52       running  (cuserid())  or  the  user  who logged in this session (getlo‐
53       gin()).  (These can differ when set-user-ID programs are involved.)
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55       For most purposes, it is more useful to use  the  environment  variable
56       LOGNAME  to  find out who the user is.  This is more flexible precisely
57       because the user can set LOGNAME arbitrarily.
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RETURN VALUE

60       getlogin() returns a pointer to the username when successful, and  NULL
61       on  failure, with errno set to indicate the cause of the error.  getlo‐
62       gin_r() returns 0 when successful, and nonzero on failure.
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ERRORS

65       POSIX specifies
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67       EMFILE The per-process limit on the number of open file descriptors has
68              been reached.
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70       ENFILE The system-wide limit on the total number of open files has been
71              reached.
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73       ENXIO  The calling process has no controlling terminal.
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75       ERANGE (getlogin_r) The length of the username, including the terminat‐
76              ing null byte ('\0'), is larger t