gethostname(2)                                          System Calls Manual                                          gethostname(2)

       gethostname, sethostname - get/set hostname

       Standard C library (libc, -lc)

       #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 asso‐
       ciated 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 glibc 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  termi‐
       nating 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 glibc 2.2 handle the case where the length of the nodename was greater than or equal to len differ‐
       ently: nothing is copied into name and the function returns -1 with errno set to ENAMETOOLONG.

       hostname(1), getdomainname(2), setdomainname(2), uname(2), uts_namespaces(7)

Linux man-pages 6.03                                         2023-02-05                                              gethostname(2)