uname - glibc

Split from the chapter glibc: System Management into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#include <sys/utsname.h>

int uname(struct utsname *buf);   /* sys/utsname.h:81 */

struct utsname {                  /* sys/utsname.h:48-70 */
    char sysname[_UTSNAME_SYSNAME_LENGTH];    /* e.g. "Linux" */
    char nodename[_UTSNAME_NODENAME_LENGTH];  /* hostname slot */
    char release[_UTSNAME_RELEASE_LENGTH];    /* e.g. "6.1.0" */
    char version[_UTSNAME_VERSION_LENGTH];
    char machine[_UTSNAME_MACHINE_LENGTH];    /* e.g. "x86_64" */
#ifdef __USE_GNU
    char domainname[_UTSNAME_DOMAIN_LENGTH];  /* NIS domain */
#else
    char __domainname[_UTSNAME_DOMAIN_LENGTH];
#endif
};

Array length: _UTSNAME_LENGTH is 65 on Linux (__NEW_UTS_LEN + 1); the fields are NUL-terminated but POSIX leaves the array sizes unspecified (uname.2 DESCRIPTION/NOTES).

Semantics

uname returns kernel-identified facts in buf and 0; only the first five members are POSIX. Four fields are meaningful (OS name, release, version, machine); nodename is the name the kernel was told via sethostname(2) – “the name of the present machine in some undefined network” – and domainname is the setdomainname(2) slot, a GNU extension that glibc exposes under __USE_GNU (uname.2 DESCRIPTION and NOTES). On Linux the glibc wrapper passes through to the uname syscall (raw page: uname); the same kernel strings back gethostname/getdomainname, which are library-level copies out of nodename/domainname. The manual uses uname for “Platform Type” detection – release for kernel features, machine for architecture dispatch (sysinfo.texi, Platform Type).

Gotchas and portability

• sysname/release/version are kernel strings, not distro identity; parsing release for distro versioning is wrong – use /etc/os-release data for that.
• nodename == hostname holds on Linux, but POSIX does not require it (uname.2 NOTES).
• Old syscall variants (olduname, oldolduname) survive in the man cache only as historical entries; glibc exposes just uname.
• domainname member visibility changes struct layout between __USE_GNU and strict builds – do not binary-copy struct utsname across compilation modes.
• musl 1.2.5: present (include/sys/utsname.h), same struct shape.

Errors

EFAULT (buf invalid) is the only documented error (uname.2 ERRORS).

References

• man2: uname.2 (see also olduname.2, oldolduname.2 for history)
• glibc manual: sysinfo.texi, nodes Platform Type, Host Identification
• headers: /usr/include/x86_64-linux-gnu/sys/utsname.h (lines 31-81)
• symbols: nm -D --with-symbol-versions libc.so.6