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UNAME(2) Linux Programmer's Manual UNAME(2)
NAME
uname - get name and information about current kernel
SYNOPSIS
#include <sys/utsname.h>
int uname(struct utsname *buf);
DESCRIPTION
uname() returns system information in the structure pointed to by buf. The utsname struct
is defined in <sys/utsname.h>:
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
};
The length of the arrays in a struct utsname is unspecified (see NOTES); the fields are
terminated by a null byte ('\0').
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT buf is not valid.
CONFORMING TO
SVr4, POSIX.1-2001. There is no uname() call in 4.3BSD.
The domainname member (the NIS or YP domain name) is a GNU extension.
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 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
domainname field.
To this end, Linux uses the system calls sethostname(2) and setdomainname(2). Note that
there is no standard that says that the hostname set by sethostname(2) is the same string
as the nodename field of the struct returned by uname() (indeed, some systems allow a
256-byte hostname and an 8-byte nodename), but this is true on Linux. The same holds for
setdomainname(2) and the domainname field.
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.
Part of the utsname information is also accessible via /proc/sys/kernel/{ostype, hostname,
osrelease, version, domainname}.
C library/kernel ABI differences
Over time, increases in the size of the utsname structure have led to three successive
versions of uname(): sys_olduname() (slot __NR_oldolduname), sys_uname() (slot
__NR_olduname), and sys_newuname() (slot __NR_uname). The first one used length 9 for all
fields; the second used 65; the third also uses 65 but adds the domainname field. The
glibc uname() wrapper function hides these details from applications, invoking the most
recent version of the system call provided by the kernel.
SEE ALSO
uname(1), getdomainname(2), gethostname(2), namespaces(7)
COLOPHON
This page is part of release 3.74 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2014-09-21 UNAME(2)
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