gethostname, sethostname - get/set hostname
#include <unistd.h>
int gethostname(char *name, size_t len);
int sethostname(const char *name, size_t
len);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
gethostname():
Since glibc 2.12: _BSD_SOURCE ||
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200112L
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)
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
len argument specifies the number of bytes in
name. (Thus,
name does not require a terminating null byte.)
gethostname() returns the null-terminated hostname in the character array
name, which has a length of
len bytes. If the null-terminated
hostname is too large to fit, then the name is truncated, and no error is
returned (but see NOTES below). POSIX.1 says that if such truncation occurs,
then it is unspecified whether the returned buffer includes a terminating null
byte.
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
- EFAULT
- name is an invalid address.
- EINVAL
- len is negative or, for sethostname(), len is larger
than the maximum allowed size.
- ENAMETOOLONG
- (glibc gethostname()) len is smaller than the actual size.
(Before version 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)).
SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD). POSIX.1-2001 and
POSIX.1-2008 specify
gethostname() but not
sethostname().
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).
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
len 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
len, 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.
Versions of glibc before 2.2 handle the case where the length of the
nodename was greater than or equal to
len differently: nothing
is copied into
name and the function returns -1 with
errno set
to
ENAMETOOLONG.
hostname(1),
getdomainname(2),
setdomainname(2),
uname(2),
uts_namespaces(7)