uname(2) System Calls Manual uname(2)
NAME
uname - get name and information about current kernel
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/utsname.h>
int uname(struct utsname *buf);
DESCRIPTION
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
NOTES); the fields are terminated by a null byte ('\0').
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set to indicate the error.
ERRORS
EFAULT buf is not valid.
STANDARDS
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD.
The domainname member (the NIS or YP domain name) is a GNU extension.
NOTES
The kernel has the name, release, version, and supported machine type
built in. Conversely, the nodename field is configured by the adminis-
trator to match the network (this is what the BSD historically calls
the "hostname", and is set via sethostname(2)). Similarly, the domain-
name field is set via setdomainname(2).
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.
Part of the utsname information is also accessible via /proc/sys/ker-
nel/{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 applica-
tions, invoking the most recent version of the system call provided by
the kernel.
SEE ALSO
uname(1), getdomainname(2), gethostname(2), uts_namespaces(7)
Linux man-pages 6.03 2023-02-05 uname(2)
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