1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
5 .\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net>:
6 .\" 'gethostname' is real system call on Linux/Alpha.
7 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
8 .\" Modified 2000-06-04, 2001-12-15 by aeb
9 .\" Modified 2004-06-17 by mtk
10 .\" Modified 2008-11-27 by mtk
12 .TH GETHOSTNAME 2 2021-03-22 "Linux man-pages (unreleased)"
14 gethostname, sethostname \- get/set hostname
17 .RI ( libc ", " \-lc )
20 .B #include <unistd.h>
22 .BI "int gethostname(char *" name ", size_t " len );
23 .BI "int sethostname(const char *" name ", size_t " len );
27 Feature Test Macro Requirements for glibc (see
28 .BR feature_test_macros (7)):
33 _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
34 || /* Glibc 2.19 and earlier */ _BSD_SOURCE
35 .\" The above is something of a simplification
36 .\" also in glibc before 2.3 there was a bit churn
42 .\" commit 266865c0e7b79d4196e2cc393693463f03c90bd8
44 In glibc 2.19 and 2.20:
45 _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
46 Up to and including glibc 2.19:
47 _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
50 These system calls are used to access or to change the system hostname.
51 More precisely, they operate on the hostname associated with the calling
52 process's UTS namespace.
55 sets the hostname to the value given in the character array
59 argument specifies the number of bytes in
63 does not require a terminating null byte.)
66 returns the null-terminated hostname in the character array
71 If the null-terminated hostname is too large to fit,
72 then the name is truncated, and no error is returned (but see NOTES below).
73 POSIX.1 says that if such truncation occurs,
74 then it is unspecified whether the returned buffer
75 includes a terminating null byte.
77 On success, zero is returned.
78 On error, \-1 is returned, and
80 is set to indicate the error.
85 is an invalid address.
90 .\" Can't occur for gethostbyname() wrapper, since 'len' has an
91 .\" unsigned type; can occur for the underlying system call.
95 is larger than the maximum allowed size.
98 .RB "(glibc " gethostname ())
100 is smaller than the actual size.
101 (Before version 2.1, glibc uses
108 the caller did not have the
110 capability in the user namespace associated with its UTS namespace (see
113 SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).
114 POSIX.1-2001 and POSIX.1-2008 specify
119 SUSv2 guarantees that "Host names are limited to 255 bytes".
120 POSIX.1 guarantees that "Host names (not including
121 the terminating null byte) are limited to
126 is defined with the value 64, which has been the limit since Linux 1.0
127 (earlier kernels imposed a limit of 8 bytes).
128 .SS C library/kernel differences
129 The GNU C library does not employ the
131 system call; instead, it implements
133 as a library function that calls
137 bytes from the returned
141 Having performed the copy, the function then checks if the length of the
143 was greater than or equal to
145 and if it is, then the function returns \-1 with
149 in this case, a terminating null byte is not included in the returned
152 Versions of glibc before 2.2
153 .\" At least glibc 2.0 and 2.1, older versions not checked
154 handle the case where the length of the
156 was greater than or equal to
158 differently: nothing is copied into
160 and the function returns \-1 with
166 .BR getdomainname (2),
167 .BR setdomainname (2),
169 .BR uts_namespaces (7)