man2/uname.2

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
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  23 .\" 2007-07-05 mtk: Added details on underlying system call interfaces
  24 .\"
  25 .TH UNAME 2 2007-07-05 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 uname \- get name and information about current kernel
  28 .SH SYNOPSIS
  29 .B #include <sys/utsname.h>
  30 .sp
  31 .BI "int uname(struct utsname *" buf );
  32 .SH DESCRIPTION
  33 .BR uname ()
  34 returns system information in the structure pointed to by
  35 .IR buf .
  36 The
  37 .I utsname
  38 struct is defined in
  39 .IR <sys/utsname.h> :
  40 .in +4n
  41 .nf
  42
  43 struct utsname {
  44     char sysname[];
  45     char nodename[];
  46     char release[];
  47     char version[];
  48     char machine[];
  49 #ifdef _GNU_SOURCE
  50     char domainname[];
  51 #endif
  52 };
  53
  54 .fi
  55 .in
  56 The length of the arrays in a
  57 .I struct utsname
  58 is unspecified; the fields are terminated by a null byte (\(aq\\0\(aq).
  59 .SH "RETURN VALUE"
  60 On success, zero is returned.
  61 On error, \-1 is returned, and
  62 .I errno
  63 is set appropriately.
  64 .SH ERRORS
  65 .TP
  66 .B EFAULT
  67 .I buf
  68 is not valid.
  69 .SH "CONFORMING TO"
  70 SVr4, POSIX.1-2001.
  71 There is no
  72 .BR uname ()
  73 call in 4.3BSD.
  74 .PP
  75 The
  76 .I domainname
  77 member (the NIS or YP domain name) is a GNU extension.
  78 .SH NOTES
  79 This is a system call, and the operating system presumably knows
  80 its name, release and version.
  81 It also knows what hardware it runs on.
  82 So, four of the fields of the struct are meaningful.
  83 On the other hand, the field \fInodename\fP is meaningless:
  84 it gives the name of the present machine in some undefined
  85 network, but typically machines are in more than one network
  86 and have several names.
  87 Moreover, the kernel has no way of knowing
  88 about such things, so it has to be told what to answer here.
  89 The same holds for the additional \fIdomainname\fP field.
  90 .LP
  91 To this end Linux uses the system calls
  92 .BR sethostname (2)
  93 and
  94 .BR setdomainname (2).
  95 Note that there is no standard that says that the hostname set by
  96 .BR sethostname (2)
  97 is the same string as the \fInodename\fP field of the struct returned by
  98 .BR uname ()
  99 (indeed, some systems allow a 256-byte hostname and an 8-byte nodename),
 100 but this is true on Linux.
 101 The same holds for
 102 .BR setdomainname (2)
 103 and the \fIdomainname\fP field.
 104 .LP
 105 The length of the fields in the struct varies.
 106 Some operating systems
 107 or libraries use a hardcoded 9 or 33 or 65 or 257.
 108 Other systems use
 109 .B SYS_NMLN
 110 or
 111 .B _SYS_NMLN
 112 or
 113 .B UTSLEN
 114 or
 115 .BR _UTSNAME_LENGTH .
 116 Clearly, it is a bad
 117 idea to use any of these constants; just use sizeof(...).
 118 Often 257 is chosen in order to have room for an internet hostname.
 119 .LP
 120 Part of the utsname information is also accessible via
 121 .BR sysctl (2)
 122 and via
 123 .IR /proc/sys/kernel/ { ostype ,
 124 .IR hostname ,
 125 .IR osrelease ,
 126 .IR version ,
 127 .IR domainname }.
 128 .SS Underlying kernel interface
 129 .LP
 130 Over time, increases in the size of the
 131 .I utsuname
 132 structure have led to three successive versions of
 133 .BR uname ():
 134 .IR sys_olduname ()
 135 (slot
 136 .IR __NR_oldolduname ),
 137 .IR sys_uname ()
 138 (slot
 139 .IR __NR_olduname ),
 140 and
 141 .IR sys_newuname ()
 142 (slot
 143 .IR __NR_uname) .
 144 The first one used length 9 for all fields;
 145 the second used 65;
 146 the third also uses 65 but adds the \fIdomainname\fP field.
 147 The glibc
 148 .BR uname ()
 149 wrapper function hides these details from applications,
 150 invoking the most recent version of the system call provided by the kernel.
 151 .SH "SEE ALSO"
 152 .BR uname (1),
 153 .BR getdomainname (2),
 154 .BR gethostname (2)