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 VERSIONS and HISTORY); 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.

VERSIONS
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—.

STANDARDS
POSIX.1-2024.

HISTORY
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.

NOTES
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}.

SEE ALSO
uname(1), getdomainname(2), gethostname(2), uts_namespaces(7)