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

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

       #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)

       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  resembles  the
       Internet  address  for  the  local machine, as returned by gethostbyname(3), and thus usually never needs to be

       The sethostid() call is restricted to the superuser.

       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.

       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.

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

       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.)

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

       hostid(1), gethostbyname(3)

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2009-01-13                      GETHOSTID(3)