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       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 to indicate the


       EFAULT buf is not valid.


       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.


       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.


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


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