centos开启telnet服务

1. 查看linux版本信息:

[loong@localhost ~]$ cat /etc/issue
CentOS 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 telnet
telnet-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,下载地址:http://rpmfind.net/linux/rpm2html/search.php?query=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 telnet
telnet-0.17-39.el5
telnet-server-0.17-39.el5

4. 启动telnet服务

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

在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 = yes 的yes改为no.

修改后:

复制代码
# 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
}
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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 restart
Stopping xinetd:                                           [  OK  ]
Starting xinetd:                                           [  OK  ]

或:

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

5. 测试服务

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[root@localhost loong]# telnet localhost
Trying 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 i686
login: loong
Password: 
Last login: Tue Apr 24 16:42:06 from 10.108.14.135
[loong@localhost ~]$ exit
logout

Connection closed by foreign host.
[root@localhost loong]# 
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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:

复制代码
telnet> o localhost
Trying 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 i686
login: root
Password: 
Login incorrect

login:     
Login incorrect

login: 
Login incorrect

login: 
Connection closed by foreign host.
[root@localhost loong]# tail -20 /var/log/secure
Apr 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
复制代码

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.so

1 #%PAM-1.0
2 #auth       required     pam_securetty.so
3 auth       include      system-auth

注:不建议开放telnet的root登录,容易带来安全隐患。

提示错误bash: telnet: command not found

解决方式,重装一下telnet客户端。
centos、ubuntu
yum list telnet*   查看telnet相关的安装包
yum install telnet-server 安装telnet服务
yum install telnet.* 安装telnet客户端


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