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[]; /* 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 ('\0').
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
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
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
}.
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.