noble (2) gethostname.2.gz

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NAME

       gethostname, sethostname - get/set hostname

LIBRARY

       Standard C library (libc, -lc)

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():
           _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
               || /* glibc 2.19 and earlier */ _BSD_SOURCE

       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 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.

RETURN VALUE

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

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 glibc 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)).

VERSIONS

       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.

STANDARDS

       gethostname()
              POSIX.1-2008.

       sethostname()
              None.

HISTORY

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

       Versions of glibc before glibc 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), uts_namespaces(7)