mirror of https://github.com/mkerrisk/man-pages
180 lines
4.7 KiB
Groff
180 lines
4.7 KiB
Groff
.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net>:
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.\" 'gethostname' is real system call on Linux/Alpha.
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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2000-06-04, 2001-12-15 by aeb
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.\" Modified 2004-06-17 by mtk
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.\" Modified 2008-11-27 by mtk
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.\"
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.TH GETHOSTNAME 2 2014-08-19 "Linux" "Linux Programmer's Manual"
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.SH NAME
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gethostname, sethostname \- get/set hostname
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.SH SYNOPSIS
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.B #include <unistd.h>
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.sp
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.BI "int gethostname(char *" name ", size_t " len );
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.br
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.BI "int sethostname(const char *" name ", size_t " len );
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.PD 0
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.BR gethostname ():
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.RS 4
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Since glibc 2.12:
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_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
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.br
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|| /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200112L
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.RE
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.br
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.BR sethostname ():
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.RS 4
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_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
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.RE
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.PD
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.ad
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.SH DESCRIPTION
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These system calls are used to access or to change the hostname of the
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current processor.
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.BR sethostname ()
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sets the hostname to the value given in the character array
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.IR name .
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The
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.I len
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argument specifies the number of bytes in
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.IR name .
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(Thus,
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.I name
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does not require a terminating null byte.)
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.BR gethostname ()
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returns the null-terminated hostname in the character array
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.IR name ,
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which has a length of
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.I len
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bytes.
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If the null-terminated hostname is too large to fit,
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then the name is truncated, and no error is returned (but see NOTES below).
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POSIX.1-2001 says that if such truncation occurs,
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then it is unspecified whether the returned buffer
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includes a terminating null byte.
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.SH RETURN VALUE
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EFAULT
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.I name
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is an invalid address.
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.TP
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.B EINVAL
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.I len
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is negative
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.\" Can't occur for gethostbyname() wrapper, since 'len' has an
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.\" unsigned type; can occur for the underlying system call.
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or, for
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.BR sethostname (),
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.I len
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is larger than the maximum allowed size.
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.TP
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.B ENAMETOOLONG
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.RB "(glibc " gethostname ())
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.I len
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is smaller than the actual size.
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(Before version 2.1, glibc uses
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.BR EINVAL
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for this case.)
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.TP
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.B EPERM
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For
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.BR sethostname (),
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the caller did not have the
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.B CAP_SYS_ADMIN
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capability.
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.SH CONFORMING TO
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SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).
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POSIX.1-2001 specifies
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.BR gethostname ()
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but not
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.BR sethostname ().
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.SH NOTES
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SUSv2 guarantees that "Host names are limited to 255 bytes".
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POSIX.1-2001 guarantees that "Host names (not including
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the terminating null byte) are limited to
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.B HOST_NAME_MAX
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bytes".
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On Linux,
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.B HOST_NAME_MAX
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is defined with the value 64, which has been the limit since Linux 1.0
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(earlier kernels imposed a limit of 8 bytes).
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.SS C library/kernel ABI differences
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The GNU C library does not employ the
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.BR gethostname ()
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system call; instead, it implements
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.BR gethostname ()
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as a library function that calls
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.BR uname (2)
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and copies up to
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.I len
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bytes from the returned
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.I nodename
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field into
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.IR name .
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Having performed the copy, the function then checks if the length of the
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.I nodename
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was greater than or equal to
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.IR len ,
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and if it is, then the function returns \-1 with
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.I errno
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set to
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.BR ENAMETOOLONG ;
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in this case, a terminating null byte is not included in the returned
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.IR name .
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Versions of glibc before 2.2
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.\" At least glibc 2.0 and 2.1, older versions not checked
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handle the case where the length of the
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.I nodename
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was greater than or equal to
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.I len
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differently: nothing is copied into
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.I name
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and the function returns \-1 with
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.I errno
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set to
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.BR ENAMETOOLONG .
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.SH SEE ALSO
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.BR getdomainname (2),
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.BR setdomainname (2),
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.BR uname (2)
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