NAME

inetd - 因特網(wǎng)“超級服務(wù)”  

總覽

inetd - [ -d ] [ -q 隊列長度 ] [ 配置文件名 ]  

描述

inetd通常在系統(tǒng)啟動時由/etc/rc.local引導(dǎo)。inetd會監(jiān)聽指定internet端口是否有連接要求。當(dāng)發(fā)現(xiàn)有某個端口有連接要求時，inetd將決定由哪個服務(wù)器進程來響應(yīng)該連接要求，并調(diào)用該服務(wù)器程序。當(dāng)程序運行結(jié)束后，inetd會繼續(xù)對該端口進行監(jiān)聽（除了以下所涉及的原因）。從本質(zhì)上講，inetd可以只運行一個守護進程，該守護進程可以在需要時調(diào)用其它服務(wù)進程，從而減輕系統(tǒng)負擔(dān)。  

選項

inetd的可用選項：

-d

打開調(diào)試功能。

-q

隊列長度設(shè)置端口監(jiān)聽隊列的長度值，默認值為128。

說明

在運行時，inetd會讀取它的配置文件，默認為/etc/inetd.conf。該配置文件的每一個欄都有一個條目，欄中每一項由空格或制表符進行分隔。以井號開頭的是注釋文本。其格式如下所示：

service name 服務(wù)名

socket type 接口類型

protocol

協(xié)議名

wait/nowait[.max] 等待/不等待

user[.group] 用戶/組

server program 服務(wù)器程序

server program arguments 服務(wù)器程序參數(shù)

如果定義的是基于Sun-RPC的服務(wù)，則將包含有以下內(nèi)容：

service name/version 服務(wù)名

socket type 接口類型

rpc/protocol 協(xié)議名

wait/nowait[.max] 等待/不等待

user[.group] 用戶/組

server program 服務(wù)器程序

server program arguments 服務(wù)器程序參數(shù)

服務(wù)名指的是一個在文件/etc/services中有定義的合法服務(wù)。相對局域網(wǎng)而言（下面討論），服務(wù)名須為該服務(wù)的官方名稱（即，處于文件 /etc/services中的第一行）。當(dāng)定義一個基于Sun-RPC的服務(wù)時，此欄內(nèi)容須是一個在文件/etc/rpc中有定義的合法服務(wù)名。在斜械右側(cè)的是RPC的版本號。此版本號可以是一個單一數(shù)字，也可以是一個從低到高的版本范圍，如：“rusers/1-3”。

接口類型則是“stream”、“dgram”、“raw”、“rdm”或“seqpacket”中的一個，這取決于其數(shù)據(jù)的類型是什么。

協(xié)議名須是在文件/etc/protocols中有定義的合法協(xié)議。例如：“tcp”或“udp”?；赗PC的服務(wù)可以定義為：“rpc/tcp”或“rpc/udp”。

等待/不等待欄僅當(dāng)定義接口類型為datagram時有效（其它接口在這里都使用“不等待”）。如果希望一個數(shù)據(jù)包到達它的同儕后，服務(wù)器立刻釋放端口，使inetd可以繼續(xù)監(jiān)聽此端口，即稱為“多線程服務(wù)”，此時該欄須設(shè)為“不等待”。如果服務(wù)器都在一個端口傳輸數(shù)據(jù)包而且不會將此端口釋放，則稱此為“單一線程”，此時應(yīng)設(shè)此欄為“等待”。Comsat(8)和talkd(8)是后一種數(shù)據(jù)類型的應(yīng)用。Tftpd(8)則是一個例外，此數(shù)據(jù)服務(wù)建立的是一個虛擬的連接，為了避免競爭，此處應(yīng)設(shè)為“等待”。服務(wù)器讀在取第一個數(shù)據(jù)包后，重新建立一個新的接口供inetd繼續(xù)提供監(jiān)聽使用，而舊的接口將在處理完該任務(wù)后將自動中斷?？蛇x項后綴“max”（與“等待”可“不等待”用逗號分隔）定義inetd在60秒內(nèi)提供服務(wù)的最大進程數(shù)，缺省值為 40。

用戶欄應(yīng)包含可以使用該服務(wù)程序用戶的用戶名。此選項充許賦于inetd服務(wù)器程序低于root的權(quán)限?？梢栽谟脩裘笥枚禾柗指艏由辖M名稱，此選項可以使inetd在運行時以所定義的組身份運行而非/etc/password文件中定義的身份。如果在此定義了組名而所定義的用戶名不是root 時，該用戶所在組的名字將自動附加到此處。

服務(wù)器程序欄應(yīng)包含全路徑的服務(wù)器程序名，inetd在監(jiān)聽到某套接字上有請求時會調(diào)過該服務(wù)器程序。如果某服務(wù)由inetd內(nèi)部提供，則此處應(yīng)填“internal”。

服務(wù)器程序參數(shù)欄中應(yīng)包含所有服務(wù)器程序運行時必須的各參數(shù)。如果服務(wù)程序由inetd內(nèi)部提供，則此處應(yīng)填“internal”。

inetd通過內(nèi)部常規(guī)工作，自身也提供一些小的服務(wù)。這些服務(wù)有 “echo”、“discard”、“chargen”、“daytime”（人類語言）和“time”（以秒為單位的機器語言，從1900年1月1日零時開始計時）。所有這些服務(wù)都是基于tcp的。如想更深一步了解這些服務(wù)，可以從網(wǎng)上獲得相關(guān)RFC文檔。

inetd在接收到SIGHUP掛起信號后會重新讀取其配置文件。在重讀配置文件后，可能增加、減少或改變已有的服務(wù)。inetd在運行時會創(chuàng)建一個/var/run/inetd.pid的文件用來存放它的進程號。

另見 SEE ALSO

comsat(8), fingerd(8), ftpd(8), rexecd(8), rlogind(8), rshd(8), lnetd(8), tftpd(8)

#p#

NAME

inetd - internet ``super-server''  

SYNOPSIS

inetd [-di ] [-q queuelength ] [configuration file ]  

DESCRIPTION

Inetd should be run at boot time by /etc/rc.local (see rc(8)). If your init(8) can respawn arbitrary daemons, inetd can be run from init instead; then init will restart it if it crashes. You must use the -i option to prevent inetd from backgrounding itself, or init will become confused.

When running, inetd listens for connections on certain internet sockets. When a connection is found on one of its sockets, it looks up what service the socket corresponds to, and invokes a program to service the request. After the program is finished, it will continue to listen on the socket, except in some special cases which will be described below. Essentially, inetd allows running one daemon to invoke several others, reducing load on the system.  

OPTIONS

The options available for inetd:

-d

Turns on several kinds of debugging and make inetd behave if run in a debugger. Also implies -i

-i

Do not background; for running from init(8).

-q queuelength

Sets the size of the socket listen queue to the specified value. Default is 128.

CONFIGURATION

Upon execution, inetd reads its configuration information from a configuration file which, by default, is /etc/inetd.conf There must be an entry for each field of the configuration file, with entries for each field separated by a tab or a space. Comments are denoted by a ``#'' at the beginning of a line. There must be an entry for each field. The fields of the configuration file are as follows:

service name[@hostname]
socket type
protocol
wait/nowait[.max]
user[.group]
server program
server program arguments

To specify an Sun-RPC based service, the entry would contain these fields.

service name/version[@hostname]
socket type
rpc/protocol
wait/nowait[.max]
user[.group]
server program
server program arguments

The service-name entry is the name of a valid service in the file /etc/services For ``internal'' services (discussed below), the service name must be the official name of the service (that is, the first entry in /etc/services ) . When used to specify a Sun-RPC based service, this field is a valid RPC service name in the file /etc/rpc . The part on the right of the ``/'' is the RPC version number. This can simply be a single numeric argument or a range of versions. A range is bounded by the low version to the high version - ``rusers/1-3''

If a string of the form @hostname is appended to the service, it causes inetd to bind to the port for the service on only the specific IP address associated with hostname instead of listening on all available addresses. This can be done as many times as desired for different addresses, which permits setting up ``virtually hosted'' services. Note, however, that while you can listen to as many specific addresses as you want, kernel restrictions prevent inetd from listening to the same port on a specific address and the general address at once. hostname should be a resolvable hostname or an IP address associated with one of the interfaces of the local system.

The socket-type should be one of ``stream'' ``dgram'' ``raw'' ``rdm'' or ``seqpacket'' depending on whether the socket is a stream, datagram, raw, reliably delivered message, or sequenced packet socket.

The protocol must be a valid protocol as given in /etc/protocols Examples might be ``tcp'' or ``udp'' Rpc based services are specified with the ``rpc/tcp'' or ``rpc/udp '' service type.

The wait/nowait entry is applicable to datagram sockets only (other sockets should have a ``nowait'' entry in this space). If a datagram server connects to its peer, freeing the socket so inetd can received further messages on the socket, it is said to be a ``multi-threaded'' server, and should use the ``nowait'' entry. For datagram servers which process all incoming datagrams on a socket and eventually time out, the server is said to be ``single-threaded'' and should use a ``wait'' entry. Comsat(8) (biff(1) ) and talkd(8) are both examples of the latter type of datagram server. Tftpd(8) is an exception; it is a datagram server that establishes pseudo-connections. It must be listed as ``wait'' in order to avoid a race; the server reads the first packet, creates a new socket, and then forks and exits to allow inetd to check for new service requests to spawn new servers. The optional ``max'' suffix (separated from ``wait'' or ``nowait'' by a dot) specifies the maximum number of server instances that may be spawned from inetd within an interval of 60 seconds. When omitted, ``max'' defaults to 40.

The user entry should contain the user name of the user as whom the server should run. This allows for servers to be given less permission than root. An optional group name can be specified by appending a dot to the user name followed by the group name. This allows for servers to run with a different (primary) group id than specified in the password file. If a group is specified and user is not root, the supplementary groups associated with that user will still be set.

The server-program entry should contain the pathname of the program which is to be executed by inetd when a request is found on its socket. If inetd provides this service internally, this entry should be ``internal''

The server program arguments should be just as arguments normally are, starting with argv[0], which is the name of the program. If the service is provided internally, the word ``internal'' should take the place of this entry.  

BUILTINS

Inetd provides several ``trivial'' services internally by use of routines within itself. These services are ``echo'' ``discard'' ``chargen'' (character generator), ``daytime'' (human readable time), and ``time'' (machine readable time, in the form of the number of seconds since midnight, January 1, 1900). All of these services are tcp based. For details of these services, consult the appropriate RFC from the Network Information Center.

Inetd rereads its configuration file when it receives a hangup signal, SIGHUP Services may be added, deleted or modified when the configuration file is reread. Inetd creates a file /var/run/inetd.pid that contains its process identifier.  

SEE ALSO

comsat(8), fingerd(8), ftpd(8), rexecd(8), rlogind(8), rshd(8), telnetd(8), tftpd(8)