gethostname(2) - Linux manual page (original) (raw)

gethostname(2) System Calls Manual gethostname(2)

NAME top

   gethostname, sethostname - get/set hostname

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <unistd.h>**

   **int gethostname(char ***_name_**, size_t** _size_**);**
   **int sethostname(const char ***_name_**, size_t** _size_**);**

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 top

   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 _size_ 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 size of _size_ bytes.  If the
   null-terminated hostname is too large to fit, then the name is
   truncated, and no error is returned (but see VERSIONS below).
   POSIX.1 says that if such truncation occurs, then it is
   unspecified whether the returned buffer includes a terminating
   null byte.

RETURN VALUE top

   On success, zero is returned.  On error, -1 is returned, and _[errno](../man3/errno.3.html)_
   is set to indicate the error.

ERRORS top

   **EFAULT** _name_ is an invalid address.

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

   **ENAMETOOLONG**
          (glibc **gethostname**()) _size_ 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)](../man7/namespaces.7.html)).

VERSIONS top

   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 size 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 size, 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 top

   **gethostname**()
          POSIX.1-2008.

   **sethostname**()
          None.

HISTORY top

   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 _size_
   differently: nothing is copied into _name_ and the function returns
   -1 with _[errno](../man3/errno.3.html)_ set to **ENAMETOOLONG**.

SEE ALSO top

   [hostname(1)](../man1/hostname.1.html), [getdomainname(2)](../man2/getdomainname.2.html), [setdomainname(2)](../man2/setdomainname.2.html), [uname(2)](../man2/uname.2.html),
   [uts_namespaces(7)](../man7/uts%5Fnamespaces.7.html)

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Linux man-pages 6.10 2024-11-17 gethostname(2)

Pages that refer to this page:crontab(1), hostname(1), logger(1), pmhostname(1), getdomainname(2), syscalls(2), uname(2), gethostid(3), rcmd(3), sysconf(3), hostname(5), org.freedesktop.hostname1(5), resolv.conf(5), systemd.unit(5), capabilities(7), user_namespaces(7), uts_namespaces(7), cron(8), lsof(8), nss-myhostname(8), systemd-hostnamed.service(8)