gethostname
Section: System Calls (2)
Updated: 202-0-08
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NAME
gethostname, sethostname - get/set hostname
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <unistd.h>
int gethostname(char *name, size_t size);
int sethostname(const char *name, size_t size);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
gethostname():
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
|| /* glibc 2.19 and earlier */ _BSD_SOURCE
sethostname():
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)
DESCRIPTION
These system calls are used to access or to change the system hostname.
More precisely, they operate on the hostname associated with the calling
process's UTS namespace.
sethostname()
sets the hostname to the value given in the character array
name.
The
size
argument specifies the number of bytes in
name.
(Thus,
name
does not require a terminating null byte.)
gethostname()
returns the nul-terminated hostname in the character array
name,
which has a size of
size
bytes.
If the nul-terminated hostname is too large to fit,
then the name is truncated, and no error is returned (but see VERSIONS below).
POSIX.1 says that if such truncation occurs,
then it is unspecified whether the returned buffer
includes a terminating null byte.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set to indicate the error.
ERRORS
- EFAULT
-
name
is an invalid address.
- EINVAL
-
size
is negative
or, for
sethostname(),
size
is larger than the maximum allowed size.
- ENAMETOOLONG
-
(glibc gethostname())
size
is smaller than the actual size.
(Before glibc 2.1, glibc uses
EINVAL
for this case.)
- EPERM
-
For
sethostname(),
the caller did not have the
CAP_SYS_ADMIN
capability in the user namespace associated with its UTS namespace (see
namespaces(7)).
VERSIONS
SUSv2 guarantees that "Host names are limited to 255 bytes".
POSIX.1 guarantees that "Host names (not including
the terminating null byte) are limited to
HOST_NAME_MAX
bytes".
On Linux,
HOST_NAME_MAX
is defined with the value 64, which has been the limit since Linux 1.0
(earlier kernels imposed a limit of 8 bytes).
C library/kernel differences
The GNU C library does not employ the
gethostname()
system call;
instead,
it implements
gethostname()
as a library function that calls
uname(2)
and copies up to
size
bytes from the returned
nodename
field into
name.
Having performed the copy, the function then checks if the length of the
nodename
was greater than or equal to
size,
and if it is, then the function returns -1 with
errno
set to
ENAMETOOLONG;
in this case, a terminating null byte is not included in the returned
name.
STANDARDS
- gethostname()
-
POSIX.-2024.
- sethostname()
-
None.
HISTORY
- gethostname()
-
4.2BSD,
SVr4,
POSIX.-2001.
- sethostname()
-
4.2BSD,
SVr4.
Versions of glibc before glibc 2.2
handle the case where the length of the
nodename
was greater than or equal to
size
differently: nothing is copied into
name
and the function returns -1 with
errno
set to
ENAMETOOLONG.
SEE ALSO
hostname(1),
getdomainname(2),
setdomainname(2),
uname(2),
uts_namespaces(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- C library/kernel differences
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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