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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
GETHOSTNAME(2) Linux Programmer's Manual GETHOSTNAME(2)
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 hostname of
the current processor.
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).
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 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)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-10-08 GETHOSTNAME(2)
Pages that refer to this page: crontab(1), hostname(1), logger(1), pmhostname(1), pmsocks(1), clone(2), getdomainname(2), syscalls(2), uname(2), gethostid(3), rcmd(3), sysconf(3), hostname(5), systemd.unit(5), namespaces(7), user_namespaces(7), cron(8), lsof(8), nss-myhostname(8), systemd-hostnamed.service(8)