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



NAME
       uname - get name and information about current kernel

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 "some implementation-defined
                                     network" */
               char release[];    /* OS release (e.g., "2.6.28") */
               char version[];    /* OS 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').

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropri-
       ately.

ERRORS
       EFAULT buf is not valid.

CONFORMING TO
       SVr4, POSIX.1-2001.  There is no uname() call in 4.3BSD.

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

NOTES
       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  con-
       stants;  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}.

   Underlying kernel interface
       Over time, increases in the size of the utsname structure have led to three succes-
       sive 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
       uname(1), getdomainname(2), gethostname(2)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-12-03                          UNAME(2)

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