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Manual for uname - man 2 uname

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

       uname(1,2) - get name and information about current kernel

       #include <sys/utsname.h>

       int uname(1,2)(struct utsname *buf);

       uname(1,2)  returns  system  information in(1,8) the structure pointed to by buf.
       The utsname struct is defined in(1,8) <sys/utsname.h>:
              struct utsname {
                      char sysname[];
                      char nodename[];
                      char release[];
                      char version(1,3,5)[];
                      char machine[];
              #ifdef _GNU_SOURCE
                      char domainname[];
       The length of the arrays in(1,8) a struct utsname is unspecified; the fields
       are NUL-terminated.

       On  success,  zero is returned.  On error(8,n), -1 is returned, and errno is
       set(7,n,1 builtins) appropriately.

       EFAULT buf is not valid.

       SVr4, SVID, POSIX, X/OPEN.  There is no uname(1,2) call in(1,8) BSD 4.3.

       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(1,8) some undefined network, but typically machines are  in(1,8)  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(7,n,1 builtins)  by  sethostname(2) is the same string(3,n) as the nodename field of the
       struct returned by uname(1,2) (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(1,8) 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(1,8) order to have room for an internet hostname.

       There have been three Linux system calls uname(1,2)(). The  first  one  used
       length  9,  the second one used 65, the third one also uses 65 but adds
       the domainname field.

       Part of the utsname information is also accessible via sysctl(2,5,8)  and  via
       /proc(5,n)/sys/kernel/{ostype, hostname, osrelease, version(1,3,5), domainname}.

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

Linux 2.5.0                       2001-12-15                          UNAME(2)

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