gethostname(2)

NAME

   gethostname, sethostname - get/set hostname

SYNOPSIS

   #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)):

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

DESCRIPTION

   These  system calls are used to access or to change the hostname of the
   current processor.

   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.

RETURN VALUE

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

ERRORS

   EFAULT name is an invalid address.

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

   ENAMETOOLONG
          (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)).

CONFORMING TO

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

NOTES

   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.

SEE ALSO

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

COLOPHON

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.

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