Telnet协议是TCP/IP协议族中的一员，是Internet远程登录服务的标准协议和主要方式。
服务端程序telnetd
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| ~ # telnetd -h
telnetd: invalid option -- 'h'
BusyBox v1.23.1 (2021-04-16 11:26:22 CST) multi-call binary.
Usage: telnetd [OPTIONS]
Handle incoming telnet connections
-l LOGIN Exec LOGIN on connect
-f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue
-K Close connection as soon as login exits
(normally wait until all programs close slave pty)
-p PORT Port to listen on
-b ADDR[:PORT] Address to bind to
-F Run in foreground
-i Inetd mode
-w SEC Inetd 'wait' mode, linger time SEC
-S Log to syslog (implied by -i or without -F and -w)
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客户端程序telnet
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| ~ # telnet
BusyBox v1.23.1 (2021-04-16 11:26:22 CST) multi-call binary.
Usage: telnet [-a] [-l USER] HOST [PORT]
Connect to telnet server
-a Automatic login with $USER variable
-l USER Automatic login as USER
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问题：解决root用户无法使用telnet命令登录服务器
telnet 密码修改命令：passwd
使用tty命令查询用户登录方式，
并将登录方式添加到/etc/securetty文件中
解决办法：
在/etc/sucuretty内容中添加如下内容
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| pts/0
pts/1
pts/2
pts/3
pts/4
pts/5
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