gethostid

       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 identifier is intended
       to be unique among all Unix systems in existence.  This normally resem-
       bles  the  Internet address for the local machine, as returned by geth-
       ostbyname(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  geth-
       ostid()  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  con-
       taining 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
Linux                             2009-01-13                      GETHOSTID(3)