You can use the functions listed in this section to determine the login
name of the user who is running a process, and the name of the user who
logged in the current session. See also the function getuid and
friends (see section Reading the Persona of a Process). How this information is collected by
the system and how to control/add/remove information from the background
storage is described in section The User Accounting Database.
The getlogin function is declared in `unistd.h', while
cuserid and L_cuserid are declared in `stdio.h'.
getlogin function 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.
cuserid function returns a pointer to a string containing a
user name associated with the effective 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The use of this function is deprecated since it is marked to be withdrawn in XPG4.2 and has already been removed from newer revisions of POSIX.1.
These functions let your program identify positively the user who is running or the user who logged in this session. (These can differ when setuid programs are involved; see section The Persona of a Process.) The user cannot do anything to fool these functions.
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.
See section Standard Environment Variables.
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