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)):

       gethostid():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
       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
       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 3.54 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/.