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       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 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), uts_namespaces(7)


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