linux man page for uname

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 ('').

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

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 ker-
       nel 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 applica-
       tions, 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 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-12-03								  UNAME(2)