.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.

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.\" 2007-07-05 mtk: Added details on underlying system call interfaces

.\"

.TH UNAME 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

uname \- get name and information about current kernel

.SH SYNOPSIS

.B #include <sys/utsname.h>

.PP

.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> :

.PP

.in +4n

.EX

struct utsname {

    char sysname[];    /* Operating system name (e.g., "Linux") */

    char nodename[];   /* Name within "some implementation-defined

                          network" */

    char release[];    /* Operating system release (e.g., "2.6.28") */

    char version[];    /* Operating system version */

    char machine[];    /* Hardware identifier */

#ifdef _GNU_SOURCE

    char domainname[]; /* NIS or YP domain name */

#endif

};

.EE

.in

.PP

The length of the arrays in a

.I struct utsname

is unspecified (see NOTES);

the fields are terminated by a null byte (\(aq\\0\(aq).

.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

POSIX.1-2001, POSIX.1-2008, SVr4.

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

.I nodename

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

.I domainname

field.

.PP

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

.I nodename

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

.I domainname

field.

.PP

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

.B SYS_NMLN

or

.B _SYS_NMLN

or

.B UTSLEN

or

.BR _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.

.PP

Part of the utsname information is also accessible via

.IR /proc/sys/kernel/ { ostype ,

.IR hostname ,

.IR osrelease ,

.IR version ,

.IR domainname }.

.SS C library/kernel differences

.PP

Over time, increases in the size of the

.I utsname

structure have led to three successive versions 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

.\" That was back before Linux 1.0

used length 9 for all fields;

the second

.\" That was also back before Linux 1.0

used 65;

the third also uses 65 but adds the

.I domainname

field.

The glibc

.BR uname ()

wrapper function hides these details from applications,

invoking the most recent version of the system call provided by the kernel.

.SH SEE ALSO

.BR uname (1),

.BR getdomainname (2),

.BR gethostname (2),

.BR namespaces (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.