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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[]; /* 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.
EFAULT 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}.
C library/kernel 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.
uname(1), getdomainname(2), gethostname(2), namespaces(7)
This page is part of release 4.12 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/.
Linux 2015-07-23 UNAME(2)
Pages that refer to this page: systemd-nspawn(1), clone(2), getdomainname(2), gethostname(2), personality(2), syscalls(2), core(5), systemd.exec(5), systemd.unit(5), lvmsystemid(7), namespaces(7), signal-safety(7), modprobe(8), sm-notify(8)