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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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gethostname(2) System Calls Manual gethostname(2)
gethostname, sethostname - get/set hostname
Standard C library (libc, -lc)
#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)
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 to indicate the error.
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 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)).
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.
gethostname()
POSIX.1-2008.
sethostname()
None.
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 ENAMETOOLONG.
hostname(1), getdomainname(2), setdomainname(2), uname(2),
uts_namespaces(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
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-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 gethostname(2)
Pages that refer to this page: crontab(1), hostname(1), logger(1), pmhostname(1), getdomainname(2), syscalls(2), uname(2), gethostid(3), rcmd(3), sysconf(3), hostname(5), org.freedesktop.hostname1(5), resolv.conf(5), systemd.unit(5), capabilities(7), user_namespaces(7), uts_namespaces(7), cron(8), lsof(8), nss-myhostname(8), systemd-hostnamed.service(8)
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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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