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如何在centos下开启telnet服务

如何在centos下开启telnet服务? 1.查看linux版本信息: [loong@localhost ~]$ cat /etc/issueCentOS release 5.8…

如何在centos下开启telnet服务?

1.查看linux版本信息:

[loong@localhost ~]$ cat /etc/issueCentOS release 5.8 (Final)Kernel \r on an \m

2. 查看系统是否已安装telnet-server,linux系统上默认已经安装telnet-client(或telnet),而telnet-server需要手动安装。

[loong@localhost ~]$ rpm -qa | grep telnettelnet-0.17-39.el5

3. 安装telnet-server,若系统已安装,跳过此步。

方法一:下载RPM resource telnet-server

选择相应版本的telnet-server下载;

安装:# rpm -i telnet-server-0.17-39.el5.i386.rpm #貌似还得单独安装xinetd.

方法二:(推荐使用)

# yum install telnet-server

安装完成后:

[loong@localhost ~]$ rpm -qa | grep telnettelnet-0.17-39.el5telnet-server-0.17-39.el5

4. 启动telnet服务

方法一:System->Administration->Services 中,

On Demand Services中选中telnet

并在Background Services中选中xinetd,并点击上面的Start,即在右侧显示:xinetd (pid 15986) is running...

最后Save & Quit.

方法二:编辑/etc/xinetd.d/telnet, 将其中的 disable = yesyes改为no.

修改后:

# default: on# description: The telnet server serves telnet sessions; it uses \#       unencrypted username/password pairs for authentication.service telnet

{ disable = no flags = REUSE socket_type = stream wait = no user = root server = /usr/sbin/in.telnetd log_on_failure += USERID}

方法三:使用chkconfig命令直接开启

[root@localhost loong]# chkconfig telnet on

注:方法二和方法三,需要激活xinetd服务。方法如下:

[root@localhost loong]# service xinetd restartStopping xinetd:                                           [  OK  ]Starting xinetd:                                           [  OK  ]

或:

[root@localhost loong]# /etc/rc.d/init.d/xinetd restartStopping xinetd:                                           [  OK  ]Starting xinetd:                                           [  OK  ]

5. 测试服务

[root@localhost loong]# telnet localhostTrying 127.0.0.1...Connected to localhost.localdomain (127.0.0.1).Escape character is '^]'.CentOS release 5.8 (Final)Kernel 2.6.18-308.1.1.el5 on an i686login: loongPassword: Last login: Tue Apr 24 16:42:06 from 10.108.14.135[loong@localhost ~]$ exitlogoutConnection closed by foreign host.[root@localhost loong]#

注:默认情况下,系统只允许普通用户telnet登录,不允许root用户登录。

要想获得root权限,可以使用普通用户登录,然后执行su,来获得root权限。

或使用一下方法,允许root登录telnet:

方法一:# mv /etc/securetty /etc/securetty.bak (不建议这种方法,测试完后再改回去吧!)

或先试图使用root用户登录,不成功,然后查看系统log:

telnet> o localhostTrying 127.0.0.1...Connected to localhost.localdomain (127.0.0.1).Escape character is '^]'.CentOS release 5.8 (Final)Kernel 2.6.18-308.1.1.el5 on an i686login: rootPassword: Login incorrectlogin:     Login incorrectlogin: Login incorrectlogin: Connection closed by foreign host.[root@localhost loong]# tail -20 /var/log/secureApr 24 17:32:58 localhost login: pam_securetty(remote:auth): access denied: tty 'pts/1' is not secure !Apr 24 17:33:03 localhost login: FAILED LOGIN 1 FROM localhost FOR root, Authentication failure
可以看到 access denied: tty 'pts/1' is not secure !所以将‘pts/1’添加到/etc/securetty中,即可实现telnet的root用户登录。至于为什么?暂不清楚。方法二:修改/etc/pam.d/remote,注释掉:auth       required     pam_securetty.so1 #%PAM-1.02 #auth       required     pam_securetty.so3 auth       include      system-auth

注:不建议开放telnet的root登录,容易带来安全隐患。

相关参考:centOS教程

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