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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)):

           _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 byte.


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


       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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