1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
3 .\" %%%LICENSE_START(VERBATIM)
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13 .\" Since the Linux kernel and libraries are constantly changing, this
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18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
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25 .\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net>:
26 .\" 'gethostname' is real system call on Linux/Alpha.
27 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
28 .\" Modified 2000-06-04, 2001-12-15 by aeb
29 .\" Modified 2004-06-17 by mtk
30 .\" Modified 2008-11-27 by mtk
32 .TH GETHOSTNAME 2 2021-03-22 "Linux" "Linux Programmer's Manual"
34 gethostname, sethostname \- get/set hostname
37 .B #include <unistd.h>
39 .BI "int gethostname(char *" name ", size_t " len );
40 .BI "int sethostname(const char *" name ", size_t " len );
44 Feature Test Macro Requirements for glibc (see
45 .BR feature_test_macros (7)):
50 _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
51 || /* Glibc 2.19 and earlier */ _BSD_SOURCE
52 .\" The above is something of a simplification
53 .\" also in glibc before 2.3 there was a bit churn
59 .\" commit 266865c0e7b79d4196e2cc393693463f03c90bd8
61 In glibc 2.19 and 2.20:
62 _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
63 Up to and including glibc 2.19:
64 _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
67 These system calls are used to access or to change the system hostname.
68 More precisely, they operate on the hostname associated with the calling
69 process's UTS namespace.
72 sets the hostname to the value given in the character array
76 argument specifies the number of bytes in
80 does not require a terminating null byte.)
83 returns the null-terminated hostname in the character array
88 If the null-terminated hostname is too large to fit,
89 then the name is truncated, and no error is returned (but see NOTES below).
90 POSIX.1 says that if such truncation occurs,
91 then it is unspecified whether the returned buffer
92 includes a terminating null byte.
94 On success, zero is returned.
95 On error, \-1 is returned, and
97 is set to indicate the error.
102 is an invalid address.
107 .\" Can't occur for gethostbyname() wrapper, since 'len' has an
108 .\" unsigned type; can occur for the underlying system call.
112 is larger than the maximum allowed size.
115 .RB "(glibc " gethostname ())
117 is smaller than the actual size.
118 (Before version 2.1, glibc uses
125 the caller did not have the
127 capability in the user namespace associated with its UTS namespace (see
130 SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).
131 POSIX.1-2001 and POSIX.1-2008 specify
136 SUSv2 guarantees that "Host names are limited to 255 bytes".
137 POSIX.1 guarantees that "Host names (not including
138 the terminating null byte) are limited to
143 is defined with the value 64, which has been the limit since Linux 1.0
144 (earlier kernels imposed a limit of 8 bytes).
145 .SS C library/kernel differences
146 The GNU C library does not employ the
148 system call; instead, it implements
150 as a library function that calls
154 bytes from the returned
158 Having performed the copy, the function then checks if the length of the
160 was greater than or equal to
162 and if it is, then the function returns \-1 with
166 in this case, a terminating null byte is not included in the returned
169 Versions of glibc before 2.2
170 .\" At least glibc 2.0 and 2.1, older versions not checked
171 handle the case where the length of the
173 was greater than or equal to
175 differently: nothing is copied into
177 and the function returns \-1 with
183 .BR getdomainname (2),
184 .BR setdomainname (2),
186 .BR uts_namespaces (7)