關於telnet到RedHat Linux失敗的解決方法詳解

失敗原因：

1.telnet套件未安裝，檢查telnet套件是否已安裝：  

[root@vm-rhel root]# rpm -qa telnet
 telnet-0.17-25

 表示已安裝

 2.telnet套件已安裝，telnet-server未安裝，檢查telnet-server套件是否安裝：

[root@vm-rhel root]# rpm -qa telnet-server
 telnet-server-0.17-25

 表示已安裝

 3.telnet#設定檔問題：

[root@vm-rhel root]# cat /etc/xinetd.d/telnet
# default: on
# description: The telnet server serves telnet sessions; it uses \
#    unencrypted username/password pairs for authentication.
service telnet
{
    flags        = REUSE
    socket_type    = stream        
    wait        = no
    user        = root
    server        = /usr/sbin/in.telnetd
    log_on_failure    += USERID
    disable        = yes 
}

將disable對應的值修改為no或註解該行並重啟xinetd守護程式：service xinetd restart。

4.Linux防火牆原因，查看防火牆狀態：

[root@vm-rhel root]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
target prot opt source destination 
RH-Lokkit-0-50-INPUT all -- anywhere anywhere

Chain FORWARD (policy ACCEPT)
target prot opt source destination 
RH-Lokkit-0-50-INPUT all -- anywhere anywhere

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

Chain RH-Lokkit-0-50-INPUT (2 references)
target prot opt source destination 
ACCEPT udp -- 192.168.1.1 anywhere udp spt:domain dpts:1025:65535 
ACCEPT tcp -- anywhere anywhere tcp dpt:smtp flags:SYN,RST,ACK/SYN 
ACCEPT tcp -- anywhere anywhere tcp dpt:http flags:SYN,RST,ACK/SYN 
ACCEPT tcp -- anywhere anywhere tcp dpt:ftp flags:SYN,RST,ACK/SYN 
ACCEPT tcp -- anywhere anywhere tcp dpt:ssh flags:SYN,RST,ACK/SYN 
ACCEPT tcp -- anywhere anywhere tcp dpt:telnet flags:SYN,RST,ACK/SYN 
ACCEPT udp -- anywhere anywhere udp spts:bootps:bootpc dpts:bootps:bootpc 
ACCEPT udp -- anywhere anywhere udp spts:bootps:bootpc dpts:bootps:bootpc 
ACCEPT all -- anywhere anywhere 
ACCEPT all -- anywhere anywhere 
REJECT tcp -- anywhere anywhere tcp dpts:0:1023 flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 
REJECT tcp -- anywhere anywhere tcp dpt:nfs flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 
REJECT udp -- anywhere anywhere udp dpts:0:1023 reject-with icmp-port-unreachable 
REJECT udp -- anywhere anywhere udp dpt:nfs reject-with icmp-port-unreachable 
REJECT tcp -- anywhere anywhere tcp dpts:x11:6009 flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable 
REJECT tcp -- anywhere anywhere tcp dpt:xfs flags:SYN,RST,ACK/SYN reject-with icmp-port-unreachable

表示未關閉,如果防火牆已關閉，則不需要在/etc /sysconfig/iptables設定檔中新增：-A RH-Lokkit-0-50-INPUT -p tcp -m tcp --dport 23 --syn -j ACCEPT。

關閉防火牆：service iptables stop (重新啟動後失效：防火牆開機自動啟動)

啟動防火牆：service iptables start

#重啟防火牆： service iptables restart

禁止防火牆開機自動啟動：chkconfig iptables off

5.預設情況下Linux不允許root使用者以telnet方式登入Linux主機，若要允許root使用者登入可採用以下3方法：

  （1）修改/etc/pam.d/login設定檔

         RedHat Linux對於遠端登入的限制體現在/etc/pam.d/login檔中，把限制內容註解即可。

[root@vm-rhel root]# cat /etc/pam.d/login#%PAM-1.0auth       required    pam_securetty.so
auth       required    pam_stack.so service=system-auth
#auth       required    pam_nologin.so
account    required    pam_stack.so service=system-auth
password   required    pam_stack.so service=system-auth
session    required    pam_stack.so service=system-auth
session    optional    pam_console.so

 （2）移除/etc/securetty資料夾

          驗證規則設定在/etc/securetty檔案中，定義了root使用者只能在tty1-tty6的終端機上記錄，刪除該檔案或將其改名即可避開驗證規則從而實現root使用者以telnet方式遠端登入Linux主機。

[root@vm-rhel root]# mv /etc/securetty /etc/securetty.bak

  （3）先用一般使用者登錄，再切換到root使用者

[bboss@vm-rhel bboss]$ su root
Password: 
[root@vm-rhel bboss]#

 

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