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 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
       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
       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 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)).

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 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
       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 size 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)

Linux man-pages 6.14              2025-05-06                    gethostname(2)