gethostname(2)

1gethostname(2)                System Calls Manual               gethostname(2)
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NAME

6       gethostname, sethostname - get/set hostname
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <unistd.h>
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14       int gethostname(char *name, size_t len);
15       int sethostname(const char *name, size_t len);
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       gethostname():
20           _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
21               || /* glibc 2.19 and earlier */ _BSD_SOURCE
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23       sethostname():
24           Since glibc 2.21:
25               _DEFAULT_SOURCE
26           In glibc 2.19 and 2.20:
27               _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
28           Up to and including glibc 2.19:
29               _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
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DESCRIPTION

32       These system calls are used to access or to change the system hostname.
33       More precisely, they operate on the hostname associated with the  call‐
34       ing process's UTS namespace.
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36       sethostname() sets the hostname to the value given in the character ar‐
37       ray name.  The len argument specifies the  number  of  bytes  in  name.
38       (Thus, name does not require a terminating null byte.)
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40       gethostname() returns the null-terminated hostname in the character ar‐
41       ray name, which has a length of  len  bytes.   If  the  null-terminated
42       hostname  is too large to fit, then the name is truncated, and no error
43       is returned (but see NOTES below).  POSIX.1 says that if  such  trunca‐
44       tion  occurs,  then  it  is unspecified whether the returned buffer in‐
45       cludes a terminating null byte.
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RETURN VALUE

48       On success, zero is returned.  On error, -1 is returned, and  errno  is
49       set to indicate the error.
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ERRORS

52       EFAULT name is an invalid address.
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54       EINVAL len  is  negative  or, for sethostname(), len is larger than the
55              maximum allowed size.
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57       ENAMETOOLONG
58              (glibc gethostname()) len is smaller than the actual size.  (Be‐
59              fore glibc 2.1, glibc uses EINVAL for this case.)
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61       EPERM  For sethostname(), the caller did not have the CAP_SYS_ADMIN ca‐
62              pability in the user namespace associated with its UTS namespace
63              (see namespaces(7)).
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VERSIONS

66       SUSv2  guarantees  that "Host names are limited to 255 bytes".  POSIX.1
67       guarantees that "Host names (not including the terminating  null  byte)
68       are  limited  to  HOST_NAME_MAX bytes".  On Linux, HOST_NAME_MAX is de‐
69       fined with the value 64, which has been the limit since Linux 1.0 (ear‐
70       lier kernels imposed a limit of 8 bytes).
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72   C library/kernel differences
73       The  GNU  C  library does not employ the gethostname() system call; in‐
74       stead, it implements gethostname() as a library function that calls un‐
75       ame(2) and copies up to len bytes from the returned nodename field into
76       name.  Having performed the copy,  the  function  then  checks  if  the
77       length  of the nodename was greater than or equal to len, and if it is,
78       then the function returns -1 with errno set to  ENAMETOOLONG;  in  this
79       case, a terminating null byte is not included in the returned name.
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STANDARDS

82       gethostname()
83              POSIX.1-2008.
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85       sethostname()
86              None.
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HISTORY

89       SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).  POSIX.1-2001
90       and POSIX.1-2008 specify gethostname() but not sethostname().
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92       Versions of glibc before glibc 2.2 handle the case where the length  of
93       the  nodename  was greater than or equal to len differently: nothing is
94       copied into name and the function returns -1 with errno set  to  ENAME‐
95       TOOLONG.
96