uname(2) — Linux manual page


UNAME(2)                Linux Programmer's Manual               UNAME(2)

NAME         top

       uname - get name and information about current kernel

SYNOPSIS         top

       #include <sys/utsname.h>

       int uname(struct utsname *buf);

DESCRIPTION         top

       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 */

       The length of the arrays in a struct utsname is unspecified (see
       NOTES); the fields are terminated by a null byte ('\0').

RETURN VALUE         top

       On success, zero is returned.  On error, -1 is returned, and
       errno is set to indicate the error.

ERRORS         top

       EFAULT buf is not valid.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4.  There is no uname() call in

       The domainname member (the NIS or YP domain name) is a GNU

NOTES         top

       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,

   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.

SEE ALSO         top

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

COLOPHON         top

       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

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)