gethostname(2) System Calls Manual gethostname(2)
NAME
gethostname, sethostname - get/set hostname
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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():
_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 ar-
ray 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 ar-
ray name, which has a length of len bytes. If the null-terminated host-
name 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.
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 len is negative or, for sethostname(), len is larger than the
maximum allowed size.
ENAMETOOLONG
(glibc gethostname()) len is smaller than the actual size. (Be-
fore glibc 2.1, glibc uses EINVAL for this case.)
EPERM For sethostname(), the caller did not have the CAP_SYS_ADMIN ca-
pability 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; in-
stead, it implements gethostname() as a library function that calls un-
ame(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 ter-
minating null byte is not included in the returned name.
STANDARDS
gethostname()
POSIX.1-2008.
sethostname()
None.
HISTORY
SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD). POSIX.1-2001
and POSIX.1-2008 specify gethostname() but not sethostname().
Versions of glibc before glibc 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 ENAMETOO-
LONG.
SEE ALSO
hostname(1), getdomainname(2), setdomainname(2), uname(2), uts_name-
spaces(7)
Linux man-pages 6.9.1 2024-05-02 gethostname(2)
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