NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON
UNAME(2) Linux Programmer's Manual UNAME(2)
uname - get name and information about current kernel
#include <sys/utsname.h>
int uname(struct utsname *buf);
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[]; /* OS release (e.g., "2.6.28") */
char version[]; /* OS 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').
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
EFAULT buf is not valid.
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.
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}.
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.
uname(1), getdomainname(2), gethostname(2)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-12-03 UNAME(2)