.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" References consulted:
.\" Linux libc source code
.\" Modified 2002-08-05, Michael Kerrisk
.\" Modified 2004-10-31, Andries Brouwer
.\"
-.TH GETHOSTBYNAME 3 2008-06-19 "" "Linux Programmer's Manual"
+.TH GETHOSTBYNAME 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
gethostbyname, gethostbyaddr, sethostent, gethostent, endhostent,
h_errno,
.nf
.B #include <netdb.h>
.B extern int h_errno;
-.sp
+.PP
.BI "struct hostent *gethostbyname(const char *" name );
-.sp
+
.BR "#include <sys/socket.h>" " /* for AF_INET */"
.BI "struct hostent *gethostbyaddr(const void *" addr ,
.BI " socklen_t " len ", int " type );
-.sp
+.PP
.BI "void sethostent(int " stayopen );
-.sp
+.PP
.B void endhostent(void);
-.sp
+.PP
.BI "void herror(const char *" s );
-.sp
+.PP
.BI "const char *hstrerror(int " err );
-.sp
+.PP
/* System V/POSIX extension */
-.br
.B struct hostent *gethostent(void);
-.sp
+.PP
/* GNU extensions */
-.br
.BI "struct hostent *gethostbyname2(const char *" name ", int " af );
-.sp
+.PP
.B "int gethostent_r("
.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
.BI " struct hostent **" result ", int *" h_errnop );
-.sp
+.PP
.BI "int gethostbyaddr_r(const void *" addr ", socklen_t " len ", int " type ,
.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
.BI " struct hostent **" result ", int *" h_errnop );
-.sp
+.PP
.BI "int gethostbyname_r(const char *" name ,
.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
.BI " struct hostent **" result ", int *" h_errnop );
-.sp
+.PP
.BI "int gethostbyname2_r(const char *" name ", int " af,
.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
.BI " struct hostent **" result ", int *" h_errnop );
.fi
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.PP
+.PD 0
.ad l
.BR gethostbyname2 (),
.BR gethostent_r (),
.BR gethostbyaddr_r (),
.BR gethostbyname_r (),
.BR gethostbyname2_r ():
+.RS 4
+.TP 4
+Since glibc 2.19:
+_DEFAULT_SOURCE
+.TP 4
+Glibc versions up to and including 2.19:
+_BSD_SOURCE || _SVID_SOURCE
+.RE
+.PD
+.PP
+.PD 0
+.BR herror (),
+.BR hstrerror ():
+.RS 4
+.TP 4
+Since glibc 2.19:
+_DEFAULT_SOURCE
+.TP 4
+Glibc 2.8 to 2.19:
_BSD_SOURCE || _SVID_SOURCE
+.TP
+Before glibc 2.8:
+none
+.RE
+.PD
+.PP
+.PD 0
+.BR h_errno :
+.RS 4
+.TP 4
+Since glibc 2.19
+_DEFAULT_SOURCE || _POSIX_C_SOURCE < 200809L
+.TP 4
+Glibc 2.12 to 2.19:
+_BSD_SOURCE || _SVID_SOURCE || _POSIX_C_SOURCE < 200809L
+.TP
+Before glibc 2.12:
+none
+.RE
.ad b
+.PD
.SH DESCRIPTION
-These functions are obsolete.
+The
+.BR gethostbyname* (),
+.BR gethostbyaddr* (),
+.BR herror (),
+and
+.BR hstrerror ()
+functions are obsolete.
Applications should use
-.BR getaddrinfo (3)
+.BR getaddrinfo (3),
+.BR getnameinfo (3),
and
-.BR getnameinfo (3)
+.BR gai_strerror (3)
instead.
-
+.PP
The
.BR gethostbyname ()
function returns a structure of type
.IR name .
Here
.I name
-is either a hostname, or an IPv4 address in standard dot notation (as for
-.BR inet_addr (3)),
-or an IPv6 address in colon (and possibly dot) notation.
-(See RFC\ 1884 for the description of IPv6 addresses.)
+is either a hostname or an IPv4 address in standard dot notation (as for
+.BR inet_addr (3)).
If
.I name
-is an IPv4 or IPv6 address, no lookup is performed and
+is an IPv4 address, no lookup is performed and
.BR gethostbyname ()
simply copies
.I name
.BR gethostbyname ()
and
.BR gethostbyaddr ()
-use a combination of any or all of the name server
-.BR named (8),
-a broken out line from \fI/etc/hosts\fP, and the Network
-Information Service (NIS or YP), depending upon the contents of the
-\fIorder\fP line in
-.IR /etc/host.conf .
-.\" (See
-.\" .BR resolv+ (8)).
-The default action is to query
-.BR named (8),
-followed by
-.IR /etc/hosts .
+rely on the Name Service Switch
+.RB ( nsswitch.conf (5))
+configured sources or a local name server
+.RB ( named (8)).
+The default action is to query the Name Service Switch
+.RB ( nsswitch.conf(5))
+configured sources, failing that, a local name server
+.RB ( named (8)).
+.\"
+.SS Historical
+The
+.BR nsswitch.conf (5)
+file is the modern way of controlling the order of host lookups.
+.PP
+In glibc 2.4 and earlier, the
+.I order
+keyword was used to control the order of host lookups as defined in
+.IR /etc/host.conf
+.RB ( host.conf (5)).
+.PP
.PP
The \fIhostent\fP structure is defined in \fI<netdb.h>\fP as follows:
-.sp
+.PP
.in +4n
-.nf
-.ne 7
+.EX
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
char **h_addr_list; /* list of addresses */
}
#define h_addr h_addr_list[0] /* for backward compatibility */
-.fi
+.EE
.in
.PP
The members of the \fIhostent\fP structure are:
The official name of the host.
.TP
.I h_aliases
-An array of alternative names for the host, terminated by a NULL pointer.
+An array of alternative names for the host, terminated by a null pointer.
.TP
.I h_addrtype
The type of address; always
.TP
.I h_addr_list
An array of pointers to network addresses for the host (in network byte
-order), terminated by a NULL pointer.
+order), terminated by a null pointer.
.TP
.I h_addr
The first address in \fIh_addr_list\fP for backward compatibility.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
The
.BR gethostbyname ()
and
.BR gethostbyaddr ()
functions return the
.I hostent
-structure or a NULL pointer if an error occurs.
+structure or a null pointer if an error occurs.
On error, the
.I h_errno
variable holds an error number.
.B HOST_NOT_FOUND
The specified host is unknown.
.TP
-.BR NO_ADDRESS " or " NO_DATA
+.BR NO_DATA
The requested name is valid but does not have an IP address.
+Another type of request to the name server for this domain
+may return an answer.
+The constant
+.BR NO_ADDRESS
+is a synonym for
+.BR NO_DATA .
.TP
.B NO_RECOVERY
-A non-recoverable name server error occurred.
+A nonrecoverable name server error occurred.
.TP
.B TRY_AGAIN
A temporary error occurred on an authoritative name server.
.TP
.I /etc/nsswitch.conf
name service switch configuration
-.SH "CONFORMING TO"
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbw18 lb lbw29
+l l l.
+Interface Attribute Value
+T{
+.BR gethostbyname ()
+T} Thread safety T{
+MT-Unsafe race:hostbyname env
+.br
+locale
+T}
+T{
+.BR gethostbyaddr ()
+T} Thread safety T{
+MT-Unsafe race:hostbyaddr env
+.br
+locale
+T}
+T{
+.BR sethostent (),
+.br
+.BR endhostent (),
+.br
+.BR gethostent_r ()
+T} Thread safety T{
+MT-Unsafe race:hostent env
+.br
+locale
+T}
+T{
+.BR herror (),
+.br
+.BR hstrerror ()
+T} Thread safety MT-Safe
+T{
+.BR gethostent ()
+T} Thread safety T{
+MT-Unsafe race:hostent
+.br
+race:hostentbuf env locale
+T}
+T{
+.BR gethostbyname2 ()
+T} Thread safety T{
+MT-Unsafe race:hostbyname2
+.br
+env locale
+T}
+T{
+.BR gethostbyaddr_r (),
+.BR gethostbyname_r (),
+.BR gethostbyname2_r ()
+T} Thread safety MT-Safe env locale
+.TE
+.sp 1
+In the above table,
+.I hostent
+in
+.I race:hostent
+signifies that if any of the functions
+.BR sethostent (),
+.BR gethostent (),
+.BR gethostent_r (),
+or
+.BR endhostent ()
+are used in parallel in different threads of a program,
+then data races could occur.
+.SH CONFORMING TO
POSIX.1-2001 specifies
.BR gethostbyname (),
.BR gethostbyaddr (),
.BR endhostent (),
.BR gethostent (),
and
-.IR h_errno .
-.\" FIXME . SUSv4 removes the specs for gethostbyname(),
-.\" gethostbyaddr(), and h_errno.
+.IR h_errno ;
+.BR gethostbyname (),
+.BR gethostbyaddr (),
+and
+.IR h_errno
+are marked obsolescent in that standard.
+POSIX.1-2008 removes the specifications of
+.BR gethostbyname (),
+.BR gethostbyaddr (),
+and
+.IR h_errno ,
+recommending the use of
+.BR getaddrinfo (3)
+and
+.BR getnameinfo (3)
+instead.
.SH NOTES
The functions
.BR gethostbyname ()
Copying the
.I struct hostent
does not suffice, since it contains pointers; a deep copy is required.
-.LP
+.PP
In the original BSD implementation the
.I len
argument
which is OK.)
See also
.BR accept (2).
-.LP
+.PP
The BSD prototype for
.BR gethostbyaddr ()
uses
-.I const char *
+.I "const char\ *"
for the first argument.
-.LP
-POSIX.1-2001 marks
-.BR gethostbyaddr ()
-and
-.BR gethostbyname ()
-obsolescent.
-.\" FIXME . SUSv4 removes the specs for gethostbyname(),
-.\" gethostbyaddr(), and h_errno.
-See
-.BR getaddrinfo (3),
-.BR getnameinfo (3),
-.BR gai_strerror (3).
-.SS "System V/POSIX Extension"
+.SS System V/POSIX extension
POSIX requires the
.BR gethostent ()
-call, that should return the next entry in the host data base.
+call, which should return the next entry in the host data base.
When using DNS/BIND this does not make much sense, but it may
be reasonable if the host data base is a file that can be read
line by line.
-On many systems a routine of this name reads
+On many systems, a routine of this name reads
from the file
.IR /etc/hosts .
-.\" e.g., Linux, FreeBSD, Unixware, HP-UX
+.\" e.g., Linux, FreeBSD, UnixWare, HP-UX
It may be available only when the library was built without DNS support.
.\" e.g., FreeBSD, AIX
The glibc version will ignore ipv6 entries.
This function is not reentrant,
and glibc adds a reentrant version
.BR gethostent_r ().
-.SS "GNU Extensions"
+.SS GNU extensions
Glibc2 also has a
.BR gethostbyname2 ()
that works like
.BR gethostbyname (),
but permits to specify the address family to which the address must belong.
-.LP
+.PP
Glibc2 also has reentrant versions
.BR gethostent_r (),
.BR gethostbyaddr_r (),
or if no entry is found
.I result
will be NULL.
-The functions return 0 on success and a non-zero error number on failure.
-In addition to the errors returned by the non-reentrant
+The functions return 0 on success and a nonzero error number on failure.
+In addition to the errors returned by the nonreentrant
versions of these functions, if
.I buf
is too small, the functions will return
does not recognize components of a dotted IPv4 address string
that are expressed in hexadecimal.
.\" http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=482973
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR getaddrinfo (3),
.\" .BR getipnodebyaddr (3),
.\" .BR getipnodebyname (3),
projects / thirdparty / man-pages.git / blobdiff