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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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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 to indicate the error.
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), uts_namespaces(7)
This page is part of release 5.13 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 2021-03-22 UNAME(2)
Pages that refer to this page: arch(1), systemd-nspawn(1), uname(1), getdomainname(2), gethostname(2), personality(2), syscalls(2), core(5), org.freedesktop.hostname1(5), systemd.exec(5), systemd.unit(5), lvmsystemid(7), signal-safety(7), uts_namespaces(7), modprobe(8), sm-notify(8), systemd-sysext(8)
Copyright and license for this manual page
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