1UNAME(2) Linux Programmer's Manual UNAME(2)
2
6 uname - get name and information about current kernel
7
9 #include <sys/utsname.h>
10 int uname(struct utsname *buf);
12
14 uname() returns system information in the structure pointed to by buf.
15 The utsname struct is defined in <sys/utsname.h>:
16 struct utsname {
18 char sysname[]; /* Operating system name (e.g., "Linux") */
19 char nodename[]; /* Name within "some implementation-defined
20 network" */
21 char release[]; /* Operating system release
22 (e.g., "2.6.28") */
23 char version[]; /* Operating system version */
24 char machine[]; /* Hardware identifier */
25 #ifdef _GNU_SOURCE
26 char domainname[]; /* NIS or YP domain name */
27 #endif
28 };
29 The length of the arrays in a struct utsname is unspecified (see
31 NOTES); the fields are terminated by a null byte ('\0').
32
34 On success, zero is returned. On error, -1 is returned, and errno is
35 set to indicate the error.
36
38 EFAULT buf is not valid.
39
41 POSIX.1-2001, POSIX.1-2008, SVr4. There is no uname() call in 4.3BSD.
42 The domainname member (the NIS or YP domain name) is a GNU extension.
44
46 This is a system call, and the operating system presumably knows its
47 name, release, and version. It also knows what hardware it runs on.
48 So, four of the fields of the struct are meaningful. On the other
49 hand, the field nodename is meaningless: it gives the name of the
50 present machine in some undefined network, but typically machines are
51 in more than one network and have several names. Moreover, the kernel
52 has no way of knowing about such things, so it has to be told what to
53 answer here. The same holds for the additional domainname field.
54 To this end, Linux uses the system calls sethostname(2) and setdomain‐
56 name(2). Note that there is no standard that says that the hostname
57 set by sethostname(2) is the same string as the nodename field of the
58 struct returned by uname() (indeed, some systems allow a 256-byte host‐
59 name and an 8-byte nodename), but this is true on Linux. The same
60 holds for setdomainname(2) and the domainname field.
61 The length of the fields in the struct varies. Some operating systems
63 or libraries use a hardcoded 9 or 33 or 65 or 257. Other systems use
64 SYS_NMLN or _SYS_NMLN or UTSLEN or _UTSNAME_LENGTH. Clearly, it is a
65 bad idea to use any of these constants; just use sizeof(...). Often
66 257 is chosen in order to have room for an internet hostname.
67 Part of the utsname information is also accessible via /proc/sys/ker‐
69 nel/{ostype, hostname, osrelease, version, domainname}.
70 C library/kernel differences
72 Over time, increases in the size of the utsname structure have led to
73 three successive versions of uname(): sys_olduname() (slot
74 __NR_oldolduname), sys_uname() (slot __NR_olduname), and sys_newuname()
75 (slot __NR_uname). The first one used length 9 for all fields; the
76 second used 65; the third also uses 65 but adds the domainname field.
77 The glibc uname() wrapper function hides these details from applica‐
78 tions, invoking the most recent version of the system call provided by
79 the kernel.
80
82 uname(1), getdomainname(2), gethostname(2), uts_namespaces(7)
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85 This page is part of release 5.12 of the Linux man-pages project. A
86 description of the project, information about reporting bugs, and the
87 latest version of this page, can be found at
88 https://www.kernel.org/doc/man-pages/.
89Linux 2021-03-22 UNAME(2)