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gethostname() - Unix, Linux System Call

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gethostname, sethostname - get/set host name


#include <unistd.h>

int gethostname(char *name, size_t len);
int sethostname(const char *name, size_t len);


These system calls are used to access or to change the host name of the current processor. The gethostname() system call returns a null-terminated hostname (set earlier by sethostname()) in the array name that has a length of len bytes. In case the null-terminated hostname does not fit, no error is returned, but the hostname is truncated. It is unspecified whether the truncated hostname will be null-terminated.


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, or, for gethostname() on Linux/i386, len is smaller than the actual size. (In this last case glibc 2.1 uses ENAMETOOLONG.)
EPERM For sethostname(), the caller did not have the CAP_SYS_ADMIN capability.


SVr4, 4.4BSD (this interfaces first appeared in 4.2BSD). POSIX.1-2001 specifies gethostname() but not sethostname().


SUSv2 guarantees that ‘Host names are limited to 255 bytes’. POSIX.1-2001 guarantees that ‘Host names (not including the terminating null byte) are limited to HOST_NAME_MAX bytes’.


The GNU C library 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. 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 ENAMETOOLONG.


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