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[];    /* 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 */
       #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 appropriately.

ERRORS

   EFAULT buf is not valid.

CONFORMING TO

   POSIX.1-2001, POSIX.1-2008, SVr4.  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 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}.

   C library/kernel 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
   applications,  invoking  the  most  recent  version  of the system call
   provided by the kernel.

SEE ALSO

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

COLOPHON

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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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