GETHOSTID(3)                                        Linux Programmer's Manual                                       GETHOSTID(3)



NAME
       gethostid, sethostid - get or set the unique identifier of the current host

SYNOPSIS
       #include <unistd.h>

       long gethostid(void);
       int sethostid(long hostid);

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

       sethostid(): _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

DESCRIPTION
       gethostid() and sethostid() respectively get or set a unique 32-bit identifier for the current machine.  The 32-bit iden-
       tifier is intended to be unique among all Unix systems in existence.  This normally resembles the  Internet  address  for
       the local machine, as returned by gethostbyname(3), and thus usually never needs to be set.

       The sethostid() call is restricted to the superuser.

RETURN VALUE
       gethostid() returns the 32-bit identifier for the current host as set by sethostid().

       On success, sethostid() returns 0; on error, -1 is returned, and errno is set to indicate the error.

ERRORS
       sethostid() can fail with the following errors:

       EACCES The caller did not have permission to write to the file used to store the host ID.

       EPERM  The calling process's effective user or group ID is not the same as its corresponding real ID.

CONFORMING TO
       4.2BSD;  these  functions were dropped in 4.4BSD.  SVr4 includes gethostid() but not sethostid().  POSIX.1-2001 specifies
       gethostid() but not sethostid().

NOTES
       In the glibc implementation, the hostid is stored in the file /etc/hostid.  (In  glibc  versions  before  2.2,  the  file
       /var/adm/hostid was used.)

       In  the  glibc  implementation,  if gethostid() cannot open the file containing the host ID, then it obtains the hostname
       using gethostname(2), passes that hostname to gethostbyname_r(3) in order to obtain the host's IPv4 address, and  returns
       a value obtained by bit-twiddling the IPv4 address.  (This value may not be unique.)

BUGS
       It is impossible to ensure that the identifier is globally unique.

SEE ALSO
       hostid(1), gethostbyname(3)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2009-01-13                                               GETHOSTID(3)