.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
.\"
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.\" responsibility for errors or omissions, or for damages resulting from
.\" 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.
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+.\" %%%LICENSE_END
.\"
-.TH UNAME 2 2001-12-15 "Linux 2.5.0" "Linux Programmer's Manual"
+.\" 2007-07-05 mtk: Added details on underlying system call interfaces
+.\"
+.TH UNAME 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
uname \- get name and information about current kernel
.SH SYNOPSIS
.B #include <sys/utsname.h>
-.sp
+.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
+The
+.I utsname
struct is defined in
.IR <sys/utsname.h> :
-.RS
-.nf
+.PP
+.in +4n
+.EX
struct utsname {
-.in +8
-char sysname[];
-char nodename[];
-char release[];
-char version[];
-char machine[];
-.in -8
+ 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
-.in +8
-char domainname[];
-.in -8
+ char domainname[]; /* NIS or YP domain name */
#endif
};
-.fi
-.RE
+.EE
+.in
+.PP
The length of the arrays in a
.I struct utsname
-is unspecified; the fields are NUL-terminated.
-.SH "RETURN VALUE"
-On success, zero is returned. On error, \-1 is returned, and
+is unspecified (see NOTES);
+the fields are terminated by a null byte (\(aq\e0\(aq).
+.SH RETURN VALUE
+On success, zero is returned.
+On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.B EFAULT
.I buf
is not valid.
-.SH "CONFORMING TO"
-SVr4, SVID, POSIX, X/OPEN.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, SVr4.
There is no
.BR uname ()
call in 4.3BSD.
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.
+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:
+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
+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
+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 \fInodename\fP field of the struct returned by
+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
+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
+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.
-.LP
-There have been three Linux system calls \fIuname\fP(). The first one
-used length 9, the second one used 65, the third one also uses 65 but
-adds the \fIdomainname\fP field.
-.LP
+.PP
Part of the utsname information is also accessible via
-.I sysctl
-and via
.IR /proc/sys/kernel/ { ostype ,
.IR hostname ,
.IR osrelease ,
.IR version ,
.IR domainname }.
-.SH "SEE ALSO"
+.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 gethostname (2),
+.BR namespaces (7)
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