.\" 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.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
.\" 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 2004-10-31 "" "Linux Programmer's Manual"
+.TH GETHOSTBYNAME 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
gethostbyname, gethostbyaddr, sethostent, gethostent, endhostent,
-herror, hstrerror \- get network host entry
+h_errno,
+herror, hstrerror,
+gethostbyaddr_r,
+gethostbyname2, gethostbyname2_r, gethostbyname_r,
+gethostent_r \- get network host entry
.SH SYNOPSIS
.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 *"
-.br
-.BI "gethostbyaddr(const void *" addr ", int " len ", int " type );
-.sp
+.BI "struct hostent *gethostbyaddr(const void *" addr ,
+.BI " socklen_t " len ", int " type );
+.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 2
-/* SYSV/POSIX extension */
-.br
+.PP
+/* System V/POSIX extension */
.B struct hostent *gethostent(void);
-.sp 2
+.PP
/* GNU extensions */
-.br
.BI "struct hostent *gethostbyname2(const char *" name ", int " af );
-.sp
-.BI "int gethostent_r("
-.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
-.BI " struct hostent **" result ", int *" h_errnop );
-.sp
+.PP
+.B "int gethostent_r("
+.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
+.BI " struct hostent **" result ", int *" h_errnop );
+.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 );
+.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
+.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
+.BI " struct hostent **" result ", int *" h_errnop );
+.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 );
+.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
+.BI " struct hostent **" result ", int *" h_errnop );
.fi
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.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
The
+.BR gethostbyname* (),
+.BR gethostbyaddr* (),
+.BR herror (),
+and
+.BR hstrerror ()
+functions are obsolete.
+Applications should use
+.BR getaddrinfo (3),
+.BR getnameinfo (3),
+and
+.BR gai_strerror (3)
+instead.
+.PP
+The
.BR gethostbyname ()
function returns a structure of type
.I hostent
.IR name .
Here
.I name
-is either a host name, or an IPv4 address in standard dot notation,
-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
The current domain and its parents are searched unless \fIname\fP
ends in a dot.
.PP
-The \fBgethostbyaddr\fP() function returns a structure of type \fIhostent\fP
+The
+.BR gethostbyaddr ()
+function returns a structure of type \fIhostent\fP
for the given host address \fIaddr\fP of length \fIlen\fP and address type
-\fItype\fP. Valid address types are
+\fItype\fP.
+Valid address types are
.B AF_INET
and
.BR AF_INET6 .
The host address argument is a pointer to a struct of a type depending
-on the address type, for example a \fBstruct in_addr *\fP (probably
-obtained via a call to \fIinet_addr\fP()) for address type AF_INET.
+on the address type, for example a \fIstruct in_addr *\fP (probably
+obtained via a call to
+.BR inet_addr (3))
+for address type
+.BR AF_INET .
.PP
-The \fBsethostent\fP() function specifies, if \fIstayopen\fP is true (1),
-that a connected TCP socket should be used for the name server queries and
-that the connection should remain open during successive queries. Otherwise,
-name server queries will use UDP datagrams.
+The
+.BR sethostent ()
+function specifies, if \fIstayopen\fP is true (1),
+that a connected TCP socket should be used for the name server queries and
+that the connection should remain open during successive queries.
+Otherwise, name server queries will use UDP datagrams.
.PP
-The \fBendhostent\fP() function ends the use of a TCP connection for name
+The
+.BR endhostent ()
+function ends the use of a TCP connection for name
server queries.
.PP
-The (obsolete) \fBherror\fP() function prints the error message associated
-with the current value of \fIh_errno\fP on stderr.
+The (obsolete)
+.BR herror ()
+function prints the error message associated
+with the current value of \fIh_errno\fP on \fIstderr\fP.
.PP
-The (obsolete) \fBhstrerror\fP() function takes an error number
+The (obsolete)
+.BR hstrerror ()
+function takes an error number
(typically \fIh_errno\fP) and returns the corresponding message string.
.PP
-The domain name queries carried out by \fBgethostbyname\fP() and
-\fBgethostbyaddr\fP() 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 .
+The domain name queries carried out by
+.BR gethostbyname ()
+and
+.BR gethostbyaddr ()
+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
-.RS
-.nf
-.ne 7
-.ta 8n 16n 32n
+.PP
+.in +4n
+.EX
struct hostent {
- char *h_name; /* official name of host */
- char **h_aliases; /* alias list */
- int h_addrtype; /* host address type */
- int h_length; /* length of address */
- char **h_addr_list; /* list of addresses */
+ char *h_name; /* official name of host */
+ char **h_aliases; /* alias list */
+ int h_addrtype; /* host address type */
+ int h_length; /* length of address */
+ char **h_addr_list; /* list of addresses */
}
-#define h_addr h_addr_list[0] /* for backward compatibility */
-.ta
-.fi
-.RE
+#define h_addr h_addr_list[0] /* for backward compatibility */
+.EE
+.in
.PP
The members of the \fIhostent\fP structure are:
.TP
The official name of the host.
.TP
.I h_aliases
-A zero-terminated array of alternative names for the host.
+An array of alternative names for the host, terminated by a null pointer.
.TP
.I h_addrtype
The type of address; always
The length of the address in bytes.
.TP
.I h_addr_list
-A zero-terminated array of network addresses for the host in network byte
-order.
+An array of pointers to network addresses for the host (in network byte
+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. On error, the
+structure or a null pointer if an error occurs.
+On error, the
.I h_errno
variable holds an error number.
When non-NULL, the return value may point at static data, see the notes below.
.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. Try again
-later.
+A temporary error occurred on an authoritative name server.
+Try again later.
.SH FILES
.TP
.I /etc/host.conf
.TP
.I /etc/hosts
host database file
-.SH "CONFORMING TO"
-4.3BSD.
-.SH "SYSV/POSIX EXTENSION"
-POSIX requires the
+.TP
+.I /etc/nsswitch.conf
+name service switch configuration
+.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 ()
-call, that 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
-from the file
-.IR /etc/hosts .
-.\" 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 ().
-.SH "GNU EXTENSIONS"
-Glibc2 also has a
+T} Thread safety T{
+MT-Unsafe race:hostent
+.br
+race:hostentbuf env locale
+T}
+T{
.BR gethostbyname2 ()
-that works like
+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 (),
-but permits to specify the address family to which the address must belong.
-.LP
-Glibc2 also has reentrant versions
-.BR gethostbyname_r ()
+.BR gethostbyaddr (),
+.BR sethostent (),
+.BR endhostent (),
+.BR gethostent (),
and
-.BR gethostbyname2_r ().
-These return 0 on success and non-zero on error. The result of the call
-is now stored in the struct with address
-.IR ret .
-After the call,
-.RI * result
-will be NULL on error or point to the result on success.
-Auxiliary data is stored in the buffer
-.I buf
-of length
-.IR buflen .
-(If the buffer is too small, these functions will return
-.BR ERANGE .)
-No global variable
-.I h_errno
-is modified, but the address of a variable in which to store error numbers
-is passed in
-.IR h_errnop .
+.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 ()
and
.BR gethostbyaddr ()
may return pointers to static data, which may be overwritten by
-later calls. Copying the
+later calls.
+Copying the
.I struct hostent
does not suffice, since it contains pointers; a deep copy is required.
-.LP
-The SUS-v2 standard is buggy and declares the
+.PP
+In the original BSD implementation the
.I len
-parameter of
+argument
+of
+.BR gethostbyname ()
+was an
+.IR int .
+The SUSv2 standard is buggy and declares the
+.I len
+argument of
.BR gethostbyaddr ()
to be of type
.IR size_t .
.IR int ,
and
.I size_t
-is not. POSIX 1003.1-2001 makes it
+is not.
+POSIX.1-2001 makes it
.IR socklen_t ,
which is OK.)
-.LP
+See also
+.BR accept (2).
+.PP
The BSD prototype for
.BR gethostbyaddr ()
uses
-.I const char *
+.I "const char\ *"
for the first argument.
-.LP
-POSIX 1003.1-2001 marks
-.BR gethostbyaddr ()
+.SS System V/POSIX extension
+POSIX requires the
+.BR gethostent ()
+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
+from the file
+.IR /etc/hosts .
+.\" 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
+Glibc2 also has a
+.BR gethostbyname2 ()
+that works like
+.BR gethostbyname (),
+but permits to specify the address family to which the address must belong.
+.PP
+Glibc2 also has reentrant versions
+.BR gethostent_r (),
+.BR gethostbyaddr_r (),
+.BR gethostbyname_r ()
and
+.BR gethostbyname2_r ().
+The caller supplies a
+.I hostent
+structure
+.I ret
+which will be filled in on success, and a temporary work buffer
+.I buf
+of size
+.IR buflen .
+After the call,
+.I result
+will point to the result on success.
+In case of an error
+or if no entry is found
+.I result
+will be NULL.
+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
+.BR ERANGE ,
+and the call should be retried with a larger buffer.
+The global variable
+.I h_errno
+is not modified, but the address of a variable in which to store error numbers
+is passed in
+.IR h_errnop .
+.SH BUGS
.BR gethostbyname ()
-obsolescent. See
-.BR getaddrinfo (3),
-.BR getnameinfo (3),
-.BR gai_strerror (3).
-.SH "SEE ALSO"
+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
.BR getaddrinfo (3),
-.BR getipnodebyaddr (3),
-.BR getipnodebyname (3),
+.\" .BR getipnodebyaddr (3),
+.\" .BR getipnodebyname (3),
.BR getnameinfo (3),
+.BR inet (3),
.BR inet_ntop (3),
.BR inet_pton (3),
.BR resolver (3),
.BR hosts (5),
+.BR nsswitch.conf (5),
.BR hostname (7),
-.BR named (8),
-.BR resolv+ (8)
+.BR named (8)
+.\" .BR resolv+ (8)
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