GETHOSTNAME(2)             Linux Programmer's Manual            GETHOSTNAME(2)

       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
           _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

       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.

       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

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

       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-

       getdomainname(2), setdomainname(2), uname(2)

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Linux                             2015-07-23                    GETHOSTNAME(2)
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