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CentOS 7.0 - man page for olduname (centos section 2)

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 */

       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 appropriately.

       EFAULT buf is not valid.

       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.

       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}.

   Underlying kernel interface
       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)

       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at

Linux					    2008-12-03					 UNAME(2)

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