GETHOSTNAME(2)		   Linux Programmer's Manual		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 trunca-
       tion 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 names-
	      pace (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 sethost-
       name().

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	ENAME-
       TOOLONG.

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

COLOPHON
       This  page  is  part of release 4.10 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/.



Linux				  2016-10-08			GETHOSTNAME(2)