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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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gethostid(3) Library Functions Manual gethostid(3)
gethostid, sethostid - get or set the unique identifier of the
current host
Standard C library (libc, -lc)
#include <unistd.h>
long gethostid(void);
int sethostid(long hostid);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
gethostid():
Since glibc 2.20:
_DEFAULT_SOURCE || _XOPEN_SOURCE >= 500
Up to and including glibc 2.19:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
sethostid():
Since glibc 2.21:
_DEFAULT_SOURCE
In glibc 2.19 and 2.20:
_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
Up to and including glibc 2.19:
_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
was 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.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────┬───────────────┬─────────────────────────────────┐
│ Interface │ Attribute │ Value │
├─────────────┼───────────────┼─────────────────────────────────┤
│ gethostid() │ Thread safety │ MT-Safe hostid env locale │
├─────────────┼───────────────┼─────────────────────────────────┤
│ sethostid() │ Thread safety │ MT-Unsafe const:hostid │
└─────────────┴───────────────┴─────────────────────────────────┘
In the glibc implementation, the hostid is stored in the file
/etc/hostid. (Before glibc 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.)
gethostid()
POSIX.1-2008.
sethostid()
None.
4.2BSD; dropped in 4.4BSD. SVr4 and POSIX.1-2001 include
gethostid() but not sethostid().
It is impossible to ensure that the identifier is globally
unique.
hostid(1), gethostbyname(3)
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2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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Linux man-pages 6.9.1 2024-05-02 gethostid(3)
Pages that refer to this page: hostid(1), machine-id(5), attributes(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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