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uname(2) System Calls Manual uname(2)
uname - get name and information about current kernel
Standard C library (libc, -lc)
#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 communications network
to which the node is attached, if any */
char release[]; /* Operating system release
(e.g., "2.6.28") */
char version[]; /* Operating system version */
char machine[]; /* Hardware type identifier */
#ifdef _GNU_SOURCE
char domainname[]; /* NIS or YP domain name */
#endif
};
The length of the arrays in a struct utsname is unspecified (see
VERSIONS and HISTORY); the fields are terminated by a null byte
('\0').
On success, zero is returned. On error, -1 is returned, and errno
is set to indicate the error.
EFAULT buf is not valid.
The domainname member (the NIS or YP domain name) is a GNU
extension.
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(...). SVr4 uses 257, "to support Internet hostnames" —
this is the largest value likely to be encountered in the wild.
POSIX.1-2008.
POSIX.1-2001, SVr4, 4.4BSD.
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.
The kernel has the name, release, version, and supported machine
type built in. Conversely, the nodename field is configured by
the administrator to match the network (this is what the BSD
historically calls the "hostname", and is set via sethostname(2)).
Similarly, the domainname field is set via setdomainname(2).
Part of the utsname information is also accessible via
/proc/sys/kernel/{ostype, hostname, osrelease, version,
domainname}.
uname(1), getdomainname(2), gethostname(2), uts_namespaces(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨Linux man-pages 6.15 2025-05-17 uname(2)
Pages that refer to this page: arch(1), systemd-nspawn(1), uname(1), getdomainname(2), gethostname(2), personality(2), syscalls(2), kbuffer_alloc(3), core(5), org.freedesktop.hostname1(5), systemd.exec(5), systemd.unit(5), lvmsystemid(7), signal-safety(7), uts_namespaces(7), lvmdevices(8), modprobe(8), sm-notify(8), systemd-sysext(8)
