Manpage of GETHOSTNAME
GETHOSTNAMESection: Linux Programmer's Manual (2)
NAMEgethostname, sethostname - get/set hostname
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)):
- Since glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200112L
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)
DESCRIPTIONThese system calls are used to access or to change the hostname of the current processor.
sethostname() sets the hostname to the value given in the character array name. The lenargument specifies the number of bytes in name. (Thus, namedoes not require a terminating null byte.)
gethostname() returns the null-terminated hostname in the character array name, which has a length of lenbytes. 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 VALUEOn success, zero is returned. On error, -1 is returned, and errnois set appropriately.
- nameis an invalid address.
- lenis negative or, for sethostname(), lenis larger than the maximum allowed size.
- (glibc gethostname()) lenis smaller than the actual size. (Before version 2.1, glibc uses EINVALfor this case.)
- For sethostname(), the caller did not have the CAP_SYS_ADMINcapability in the user namespace associated with its UTS namespace (see namespaces(7)).
CONFORMING TOSVr4, 4.4BSD (these interfaces first appeared in 4.2BSD). POSIX.1-2001 and POSIX.1-2008 specify gethostname() but not sethostname().
NOTESSUSv2 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_MAXbytes". On Linux, HOST_NAME_MAXis 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 differencesThe 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 lenbytes from the returned nodenamefield into name. Having performed the copy, the function then checks if the length of the nodenamewas greater than or equal to len, and if it is, then the function returns -1 with errnoset to ENAMETOOLONG; in this case, a terminating null byte is not included in the returned name.
Versions of glibc before 2.2 handle the case where the length of the nodenamewas greater than or equal to lendifferently: nothing is copied into nameand the function returns -1 with errnoset to ENAMETOOLONG.
SEE ALSOhostname(1), getdomainname(2), setdomainname(2), uname(2)
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