man2/uname.2

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" 2007-07-05 mtk: Added details on underlying system call interfaces
   6 .\"
   7 .TH uname 2 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 uname \- get name and information about current kernel
  10 .SH LIBRARY
  11 Standard C library
  12 .RI ( libc ", " \-lc )
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <sys/utsname.h>
  16 .P
  17 .BI "int uname(struct utsname *" buf );
  18 .fi
  19 .SH DESCRIPTION
  20 .BR uname ()
  21 returns system information in the structure pointed to by
  22 .IR buf .
  23 The
  24 .I utsname
  25 struct is defined in
  26 .IR <sys/utsname.h> :
  27 .P
  28 .in +4n
  29 .EX
  30 struct utsname {
  31     char sysname[];    /* Operating system name (e.g., "Linux") */
  32     char nodename[];   /* Name within communications network
  33                           to which the node is attached, if any */
  34     char release[];    /* Operating system release
  35                           (e.g., "2.6.28") */
  36     char version[];    /* Operating system version */
  37     char machine[];    /* Hardware type identifier */
  38 #ifdef _GNU_SOURCE
  39     char domainname[]; /* NIS or YP domain name */
  40 #endif
  41 };
  42 .EE
  43 .in
  44 .P
  45 The length of the arrays in a
  46 .I struct utsname
  47 is unspecified (see NOTES);
  48 the fields are terminated by a null byte (\[aq]\e0\[aq]).
  49 .SH RETURN VALUE
  50 On success, zero is returned.
  51 On error, \-1 is returned, and
  52 .I errno
  53 is set to indicate the error.
  54 .SH ERRORS
  55 .TP
  56 .B EFAULT
  57 .I buf
  58 is not valid.
  59 .SH VERSIONS
  60 The
  61 .I domainname
  62 member (the NIS or YP domain name) is a GNU extension.
  63 .P
  64 The length of the fields in the struct varies.
  65 Some operating systems
  66 or libraries use a hardcoded 9 or 33 or 65 or 257.
  67 Other systems use
  68 .B SYS_NMLN
  69 or
  70 .B _SYS_NMLN
  71 or
  72 .B UTSLEN
  73 or
  74 .BR _UTSNAME_LENGTH .
  75 Clearly, it is a bad
  76 idea to use any of these constants; just use sizeof(...).
  77 SVr4 uses 257, "to support Internet hostnames"
  78 \[em] this is the largest value likely to be encountered in the wild.
  79 .SH STANDARDS
  80 POSIX.1-2008.
  81 .SH HISTORY
  82 POSIX.1-2001, SVr4, 4.4BSD.
  83 .SS C library/kernel differences
  84 Over time, increases in the size of the
  85 .I utsname
  86 structure have led to three successive versions of
  87 .BR uname ():
  88 .IR sys_olduname ()
  89 (slot
  90 .IR __NR_oldolduname ),
  91 .IR sys_uname ()
  92 (slot
  93 .IR __NR_olduname ),
  94 and
  95 .IR sys_newuname ()
  96 (slot
  97 .IR __NR_uname) .
  98 The first one
  99 .\" That was back before Linux 1.0
 100 used length 9 for all fields;
 101 the second
 102 .\" That was also back before Linux 1.0
 103 used 65;
 104 the third also uses 65 but adds the
 105 .I domainname
 106 field.
 107 The glibc
 108 .BR uname ()
 109 wrapper function hides these details from applications,
 110 invoking the most recent version of the system call provided by the kernel.
 111 .SH NOTES
 112 The kernel has the name, release, version, and supported machine type built in.
 113 Conversely, the
 114 .I nodename
 115 field is configured by the administrator to match the network
 116 (this is what the BSD historically calls the "hostname",
 117 and is set via
 118 .BR sethostname (2)).
 119 Similarly, the
 120 .I domainname
 121 field is set via
 122 .BR setdomainname (2).
 123 .P
 124 Part of the utsname information is also accessible via
 125 .IR /proc/sys/kernel/ { ostype ,
 126 .IR hostname ,
 127 .IR osrelease ,
 128 .IR version ,
 129 .IR domainname }.
 130 .SH SEE ALSO
 131 .BR uname (1),
 132 .BR getdomainname (2),
 133 .BR gethostname (2),
 134 .BR uts_namespaces (7)