mirror of https://github.com/mkerrisk/man-pages
151 lines
4.3 KiB
Groff
151 lines
4.3 KiB
Groff
.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
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.\"
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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.\" manual page may be incorrect or out-of-date.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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.\"
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.\" 2007-07-05 mtk: Added details on underlying system call interfaces
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.\"
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.TH UNAME 2 2007-07-05 "Linux" "Linux Programmer's Manual"
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.SH NAME
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uname \- get name and information about current kernel
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.SH SYNOPSIS
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.B #include <sys/utsname.h>
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.sp
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.BI "int uname(struct utsname *" buf );
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.SH DESCRIPTION
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.BR uname ()
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returns system information in the structure pointed to by
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.IR buf .
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The
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.I utsname
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struct is defined in
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.IR <sys/utsname.h> :
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.in +0.5i
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.nf
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struct utsname {
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char sysname[];
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char nodename[];
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char release[];
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char version[];
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char machine[];
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#ifdef _GNU_SOURCE
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char domainname[];
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#endif
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};
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.fi
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.in -0.5i
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The length of the arrays in a
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.I struct utsname
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is unspecified; the fields are terminated by a null byte ('\\0').
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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 buf
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is not valid.
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.SH "CONFORMING TO"
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SVr4, POSIX.1-2001.
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There is no
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.BR uname ()
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call in 4.3BSD.
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.PP
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The
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.I domainname
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member (the NIS or YP domain name) is a GNU extension.
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.SH NOTES
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This is a system call, and the operating system presumably knows
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its name, release and version.
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It also knows what hardware it runs on.
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So, four of the fields of the struct are meaningful.
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On the other hand, the field \fInodename\fP is meaningless:
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it gives the name of the present machine in some undefined
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network, but typically machines are in more than one network
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and have several names.
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Moreover, the kernel has no way of knowing
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about such things, so it has to be told what to answer here.
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The same holds for the additional \fIdomainname\fP field.
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.LP
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To this end Linux uses the system calls
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.BR sethostname (2)
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and
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.BR setdomainname (2).
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Note that there is no standard that says that the hostname set by
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.BR sethostname (2)
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is the same string as the \fInodename\fP field of the struct returned by
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.BR uname ()
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(indeed, some systems allow a 256-byte hostname and an 8-byte nodename),
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but this is true on Linux.
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The same holds for
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.BR setdomainname (2)
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and the \fIdomainname\fP field.
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.LP
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The length of the fields in the struct varies.
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Some operating systems
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or libraries use a hardcoded 9 or 33 or 65 or 257.
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Other systems use
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SYS_NMLN or _SYS_NMLN or UTSLEN or _UTSNAME_LENGTH.
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Clearly, it is a bad
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idea to use any of these constants; just use sizeof(...).
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Often 257 is chosen in order to have room for an internet hostname.
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.LP
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Part of the utsname information is also accessible via
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.BR sysctl (2)
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and via
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.IR /proc/sys/kernel/ { ostype ,
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.IR hostname ,
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.IR osrelease ,
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.IR version ,
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.IR domainname }.
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.SS Underlying kernel interface
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.LP
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Over time, increases in the size of the
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.I utsuname
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structure have led to three successive implementations of
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.BR uname ():
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.IR sys_olduname ()
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(slot
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.IR __NR_oldolduname ),
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.IR sys_uname ()
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(slot
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.IR __NR_olduname ),
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and
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.IR sys_newuname ()
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(slot
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.IR __NR_uname).
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The first one used length 9 for all fields;
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the second used 65;
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the third also uses 65 but adds the \fIdomainname\fP field.
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The glibc
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.BR uname ()
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wrapper function hides these details from applications,
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ensuring that new applications linked against
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the current library automatically use the current implementation,
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and that binary compatibility is not broken for older binaries.
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.SH "SEE ALSO"
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.BR uname (1),
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.BR getdomainname (2),
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.BR gethostname (2)
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