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)):

           _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
               || /* Glibc 2.19 and earlier */ _BSD_SOURCE

           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

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

       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 sethostname().

       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 ENAMETOOLONG.

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

       This page is part of release 5.13 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                              2021-03-22                     GETHOSTNAME(2)