GETHOSTNAME(2)             Linux Programmer's Manual            GETHOSTNAME(2)

       gethostname, sethostname - get/set hostname

       #include <unistd.h>

       int gethostname(char *name, size_t len);
       int sethostname(const char *name, size_t len);

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

           Since glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200112L
           Since glibc 2.21:
           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)

       These system calls are used to access or to change the system hostname.
       More precisely, they operate on the hostname associated with the
       calling process's UTS namespace.

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

       gethostname() returns the null-terminated hostname in the character
       array name, which has a length of len bytes.  If the null-terminated
       hostname is too large to fit, then the name is truncated, and no error
       is returned (but see NOTES below).  POSIX.1 says that if such
       truncation occurs, then it is unspecified whether the returned buffer
       includes a terminating null byte.

       On success, zero is returned.  On error, -1 is returned, and errno is
       set appropriately.

       EFAULT name is an invalid address.

       EINVAL len is negative or, for sethostname(), len is larger than the
              maximum allowed size.

              (glibc gethostname()) len is smaller than the actual size.
              (Before version 2.1, glibc uses EINVAL for this case.)

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

       SVr4, 4.4BSD  (these interfaces first appeared in 4.2BSD).
       POSIX.1-2001 and POSIX.1-2008 specify gethostname() but not

       SUSv2 guarantees that "Host names are limited to 255 bytes".  POSIX.1
       guarantees that "Host names (not including the terminating null byte)
       are limited to HOST_NAME_MAX bytes".  On Linux, HOST_NAME_MAX is
       defined with the value 64, which has been the limit since Linux 1.0
       (earlier kernels imposed a limit of 8 bytes).

   C library/kernel differences
       The GNU C library does not employ the gethostname() system call;
       instead, it implements gethostname() as a library function that calls
       uname(2) and copies up to len bytes from the returned nodename field
       into name.  Having performed the copy, the function then checks if the
       length of the nodename was greater than or equal to len, and if it is,
       then the function returns -1 with errno set to ENAMETOOLONG; in this
       case, a terminating null byte is not included in the returned name.

       Versions of glibc before 2.2 handle the case where the length of the
       nodename was greater than or equal to len differently: nothing is
       copied into name and the function returns -1 with errno set to

       hostname(1), getdomainname(2), setdomainname(2), uname(2),

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2019-10-10                    GETHOSTNAME(2)