telnetd、telnet、ssh、sshd概念
ssh and sshd
ssh is based on the application layer
ssh -------->sshd (ssh is used as the client, mainly for server-side connections; sshd is used as the server-side)
有一种命令也是sshd，这是openssh的守护进程，和sshd服务端不是一个东西
telnet与telnetd
telnet is based on the transport layer
telnet-------->telnetd (telnet is used as the client, mainly for server-side connection; telnetd is used as the server-side)
There is also telnets, which means telnet-over-ssl, based on ssl encryption
Comparison of telnet and ssh
ssh
password: certified by certificate
Data: encrypted
telnet
is nothing, it's not safe
busybox
BusyBox is a software that integrates more than 300 most commonly used Linux commands and tools.
For example, ssh and telnet
can be placed in the embedded system, which is very useful.