gethostname(2) — Linux manual page

gethostname(2)             System Calls Manual            gethostname(2)

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)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                 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)

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