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.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" 2007-07-05 mtk: Added details on underlying system call interfaces
.\"
.TH UNAME 2 2007-07-05 "Linux" "Linux Programmer's Manual"
.SH NAME
uname \- get name and information about current kernel
.SH SYNOPSIS
.B #include <sys/utsname.h>
.sp
.BI "int uname(struct utsname *" buf );
.SH DESCRIPTION
.BR uname ()
returns system information in the structure pointed to by
.IR buf .
The
.I utsname
struct is defined in
.IR <sys/utsname.h> :
.in +0.5i
.nf
struct utsname {
char sysname[];
char nodename[];
char release[];
char version[];
char machine[];
#ifdef _GNU_SOURCE
char domainname[];
#endif
};
.fi
.in -0.5i
The length of the arrays in a
.I struct utsname
is unspecified; the fields are terminated by a null byte ('\\0').
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
.I buf
is not valid.
.SH "CONFORMING TO"
SVr4, POSIX.1-2001.
There is no
.BR uname ()
call in 4.3BSD.
.PP
The
.I domainname
member (the NIS or YP domain name) is a GNU extension.
.SH NOTES
This is a system call, and the operating system presumably knows
its name, release and version.
It also knows what hardware it runs on.
So, four of the fields of the struct are meaningful.
On the other hand, the field \fInodename\fP is meaningless:
it gives the name of the present machine in some undefined
network, but typically machines are in more than one network
and have several names.
Moreover, the kernel has no way of knowing
about such things, so it has to be told what to answer here.
The same holds for the additional \fIdomainname\fP field.
.LP
To this end Linux uses the system calls
.BR sethostname (2)
and
.BR setdomainname (2).
Note that there is no standard that says that the hostname set by
.BR sethostname (2)
is the same string as the \fInodename\fP field of the struct returned by
.BR uname ()
(indeed, some systems allow a 256-byte hostname and an 8-byte nodename),
but this is true on Linux.
The same holds for
.BR setdomainname (2)
and the \fIdomainname\fP field.
.LP
The length of the fields in the struct varies.
Some operating systems
or libraries use a hardcoded 9 or 33 or 65 or 257.
Other systems use
SYS_NMLN or _SYS_NMLN or UTSLEN or _UTSNAME_LENGTH.
Clearly, it is a bad
idea to use any of these constants; just use sizeof(...).
Often 257 is chosen in order to have room for an internet hostname.
.LP
Part of the utsname information is also accessible via
.BR sysctl (2)
and via
.IR /proc/sys/kernel/ { ostype ,
.IR hostname ,
.IR osrelease ,
.IR version ,
.IR domainname }.
.SS Underlying kernel interface
.LP
Over time, increases in the size of the
.I utsuname
structure have led to three successive implementations of
.BR uname ():
.IR sys_olduname ()
(slot
.IR __NR_oldolduname ),
.IR sys_uname ()
(slot
.IR __NR_olduname ),
and
.IR sys_newuname ()
(slot
.IR __NR_uname).
The first one used length 9 for all fields;
the second used 65;
the third also uses 65 but adds the \fIdomainname\fP field.
The glibc
.BR uname ()
wrapper function hides these details from applications,
ensuring that new applications linked against
the current library automatically use the current implementation,
and that binary compatibility is not broken for older binaries.
.SH "SEE ALSO"
.BR uname (1),
.BR getdomainname (2),
.BR gethostname (2)
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