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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 setdomain-
       name(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 host-
       name  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/ker-
       nel/{ostype, hostname, osrelease, version, domainname}.

   C library/kernel ABI	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.

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

       This page is part of release 3.74 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				  2014-09-21			      UNAME(2)


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