getlogin, getlogin_r, cuserid - get username


   #include <unistd.h>

   char *getlogin(void);
   int getlogin_r(char *buf, size_t bufsize);

   #include <stdio.h>

   char *cuserid(char *string);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   getlogin_r(): _POSIX_C_SOURCE >= 199506L

       Since glibc 2.24:
           (_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
           || __GNU_SOURCE
       Up to and including glibc 2.23:


   getlogin()  returns  a  pointer  to a string containing the name of the
   user logged in on the controlling terminal of the process,  or  a  null
   pointer  if  this  information  cannot  be  determined.   The string is
   statically allocated and might be overwritten on  subsequent  calls  to
   this function or to cuserid().

   getlogin_r()  returns  this  same  username  in  the  array buf of size

   cuserid()  returns  a  pointer  to  a  string  containing  a   username
   associated with the effective user ID of the process.  If string is not
   a null pointer, it should be an array that can hold at least  L_cuserid
   characters; the string is returned in this array.  Otherwise, a pointer
   to a string in a static area is returned.  This  string  is  statically
   allocated and might be overwritten on subsequent calls to this function
   or to getlogin().

   The macro L_cuserid is an integer constant that indicates how  long  an
   array  you  might  need  to store a username.  L_cuserid is declared in

   These functions let your program identify positively the  user  who  is
   running   (cuserid())   or   the   user  who  logged  in  this  session
   (getlogin()).   (These  can  differ  when  set-user-ID   programs   are

   For  most  purposes,  it is more useful to use the environment variable
   LOGNAME to find out who the user is.  This is more  flexible  precisely
   because the user can set LOGNAME arbitrarily.


   getlogin()  returns a pointer to the username when successful, and NULL
   on failure, with  errno  set  to  indicate  the  cause  of  the  error.
   getlogin_r() returns 0 when successful, and nonzero on failure.


   POSIX specifies

   EMFILE The per-process limit on the number of open file descriptors has
          been reached.

   ENFILE The system-wide limit on the total number of open files has been

   ENXIO  The calling process has no controlling terminal.

   ERANGE (getlogin_r)   The   length   of  the  username,  including  the
          terminating null byte ('\0'), is larger than bufsize.

   Linux/glibc also has

   ENOENT There was no corresponding entry in the utmp-file.

   ENOMEM Insufficient memory to allocate passwd structure.

   ENOTTY Standard input didn't refer to a terminal.  (See BUGS.)


          password database file

          (traditionally /etc/utmp; some libc versions used /var/adm/utmp)


   For  an  explanation  of  the  terms  used   in   this   section,   see

   │InterfaceAttributeValue                                 │
   │getlogin()   │ Thread safety │ MT-Unsafe race:getlogin race:utent    │
   │             │               │ sig:ALRM timer locale                 │
   │getlogin_r() │ Thread safety │ MT-Unsafe race:utent sig:ALRM timer   │
   │             │               │ locale                                │
   │cuserid()    │ Thread safety │ MT-Unsafe race:cuserid/!string locale │
   In  the  above  table, utent in race:utent signifies that if any of the
   functions setutent(3), getutent(3), or endutent(3) are used in parallel
   in  different  threads  of  a  program,  then  data  races could occur.
   getlogin() and getlogin_r() call those functions, so we use  race:utent
   to remind users.


   getlogin() and getlogin_r(): POSIX.1-2001, POSIX.1-2008.

   System  V  has  a cuserid() function which uses the real user ID rather
   than the effective user ID.  The cuserid() function was included in the
   1988  version  of  POSIX,  but  removed  from the 1990 version.  It was
   present in SUSv2, but removed in POSIX.1-2001.

   OpenBSD has getlogin() and setlogin(), and a username associated with a
   session, even if it has no controlling terminal.


   Unfortunately,  it  is often rather easy to fool getlogin().  Sometimes
   it does not work at all, because some program messed up the utmp  file.
   Often,  it  gives  only  the first 8 characters of the login name.  The
   user currently logged in on the controlling  terminal  of  our  program
   need  not  be  the user who started it.  Avoid getlogin() for security-
   related purposes.

   Note that glibc does not follow the POSIX specification and uses  stdin
   instead of /dev/tty.  A bug.  (Other recent systems, like SunOS 5.8 and
   HP-UX 11.11 and FreeBSD 4.8 all return the login name also  when  stdin
   is redirected.)

   Nobody  knows  precisely  what  cuserid()  does;  avoid  it in portable
   programs.  Or avoid it altogether: use getpwuid(geteuid()) instead,  if
   that is what you meant.  Do not use cuserid().


   logname(1), geteuid(2), getuid(2), utmp(5)


   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at

More Linux Commands

TAILQ_ENTRY(3) implementations of lists, tail queues, and ci
These macros define and operate on three types of data structures: lists, tail queues, and circular queues. All three structures support the following functiona

getbegy(3ncurses) - get curses cursor and window coordinates
The getbegy and getbegx functions return the same data as getbegyx. The getcury and getcurx functions return the same data as getyx. The getmaxy and getmaxx fun

iso_8859_7(7) - ISO 8859-7 character set encoded in octal, d
The ISO 8859 standard includes several 8-bit extensions to the ASCII character set (also known as ISO 646-IRV). ISO 8859-7 encodes the characters used in modern

exp2(3) - base-2 exponential function - Linux manual page...
The exp2() function returns the value of 2 raised to the power of x. RETURN VALUE On success, these functions return the base-2 exponential value of x. For vari

test(1) - check file types and compare values (Man Page)....
test.1 - Exit with the status determined by EXPRESSION. --help display this help and exit --version output version information and exit An omitted EXPRESSION de

XIUngrabEnter(3) - grab/ungrab enter or focus in events.....
XIGrabEnter and XIGrabFocusIn establish a passive grab. The modifier device for a enter grab is the paired master device if deviceid specifies a master pointer.

iso_8859-16(7) - ISO 8859-16 character set encoded in octal,
The ISO 8859 standard includes several 8-bit extensions to the ASCII character set (also known as ISO 646-IRV). ISO 8859-16, the Latin Alphabet No. 10 is used t

addnstr(3ncurses) - add a string of characters to a curses w
addnstr.3ncurses - These functions write the (null-terminated) character string str on the given window. It is similar to calling waddch once for each character

register_app_config_handler(3) - netsnmp_config_api function
The functions are a fairly extensible system of parsing various configuration files at the run time of an application. The configuration file flow is broken int

ciptool(1) - Bluetooth Common ISDN Access Profile (CIP).....
ciptool is used to set up, maintain, and inspect the CIP configuration of the Bluetooth subsystem in the Linux kernel. OPTIONS -h Gives a list of possible comma

alloc_hugepages(2) - allocate or free huge pages (Man Page)
The system calls alloc_hugepages() and free_hugepages() were introduced in Linux 2.5.36 and removed again in 2.5.54. They existed only on i386 and ia64 (when bu

XwcTextPerCharExtents(3) - obtain per-character information
The XmbTextPerCharExtents, XwcTextPerCharExtents and Xutf8TextPerCharExtents functions return the text dimensions of each character of the specified text, using

We can't live, work or learn in freedom unless the software we use is free.