getdomainname(2)              System Calls Manual             getdomainname(2)

NAME
       getdomainname, setdomainname - get/set NIS domain name

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <unistd.h>

       int getdomainname(size_t size;
                         char name[size], size_t size);
       int setdomainname(size_t size;
                         const char name[size], size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getdomainname(), setdomainname():
           Since glibc 2.21:
               _DEFAULT_SOURCE
           In glibc 2.19 and 2.20:
               _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
           Up to and including glibc 2.19:
               _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

DESCRIPTION
       These functions are used to access or to change the NIS domain name of
       the host system.  More precisely, they operate on the NIS domain name
       associated with the calling process's UTS namespace.

       setdomainname() sets the domain name to the value given in the
       character array name.  The size argument specifies the number of bytes
       in name.  (Thus, name does not require a terminating null byte.)

       getdomainname() returns the null-terminated domain name in the
       character array name, which has a size of size bytes.  If the null-
       terminated domain name requires more than len bytes, getdomainname()
       returns the first len bytes (glibc) or gives an error (libc).

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is
       set to indicate the error.

ERRORS
       setdomainname() can fail with the following errors:

       EFAULT name pointed outside of user address space.

       EINVAL size was negative or too large.

       EPERM  The caller did not have the CAP_SYS_ADMIN capability in the user
              namespace associated with its UTS namespace (see namespaces(7)).

       getdomainname() can fail with the following errors:

       EINVAL For getdomainname() under libc: name is NULL or name is equal or
              longer than size bytes.

VERSIONS
       On most Linux architectures (including x86), there is no
       getdomainname() system call; instead, glibc implements getdomainname()
       as a library function that returns a copy of the domainname field
       returned from a call to uname(2).

STANDARDS
       None.

HISTORY
       Since Linux 1.0, the limit on the size of a domain name, including the
       terminating null byte, is 64 bytes.  In older kernels, it was 8 bytes.

SEE ALSO
       gethostname(2), sethostname(2), uname(2), uts_namespaces(7)

Linux man-pages 6.18              2026-02-08                  getdomainname(2)