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[]; /* 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').
On success, zero is returned. On error, -1 is returned, and
errno
is set appropriately.
buf
is not valid.
POSIX.1-2001, POSIX.1-2008, SVr4. 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), uts_namespaces(7)
This page is part of release 5.10 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
https://www.kernel.org/doc/man-pages/.