잘쓰고 있던 ftp가 갑자기 안됩니다....

/var/log/secure

/var/log/messages 에 나오는 로그도 확인이 필요해보입니다

ssh 접속이나, ftp 접속인증에 대해서는 secure로그에 이유가 남게 되어있거든요

자세한 문의는 하모니카 슬랙 채널에서 물어보심 답변해드릴게요

시스템 안의 문제는 포트를 리슨하는 상태이고 방화벽이 없다면 크게 연관된 부분이 없을것 같습니다만, 이 경우 공유기의 포트 포워딩 정상 동작 여부를 함께 확인해야 합니다. 

아래의 명령어를 사용하시면 공유기의 해당포트 접속 상태를 확인할 수 있습니다.

nmap -p <공유기에설정한 포워딩포트> -v -A -T4 <공유기에 할당된 공인 IP>

예)

$ nmap -p 11122 -v -A -T4 61.32.208.27 

결과)

Starting Nmap 7.80 ( https://nmap.org ) at 2022-11-24 11:22 KST

NSE: Loaded 151 scripts for scanning.

NSE: Script Pre-scanning.

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating Ping Scan at 11:22

Scanning 61.32.208.27 [2 ports]

Completed Ping Scan at 11:22, 0.01s elapsed (1 total hosts)

Initiating Parallel DNS resolution of 1 host. at 11:22

Completed Parallel DNS resolution of 1 host. at 11:22, 0.01s elapsed

Initiating Connect Scan at 11:22

Scanning 61.32.208.27 [1 port]

Discovered open port 11122/tcp on 61.32.208.27

Completed Connect Scan at 11:22, 0.00s elapsed (1 total ports)

Initiating Service scan at 11:22

Scanning 1 service on 61.32.208.27

Completed Service scan at 11:22, 0.02s elapsed (1 service on 1 host)

NSE: Script scanning 61.32.208.27.

Initiating NSE at 11:22

Completed NSE at 11:22, 0.30s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Nmap scan report for 61.32.208.27

Host is up (0.0055s latency).

PORT      STATE SERVICE VERSION

11122/tcp open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.5 (Ubuntu Linux; protocol 2.0)

Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

NSE: Script Post-scanning.

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Initiating NSE at 11:22

Completed NSE at 11:22, 0.00s elapsed

Read data files from: /usr/bin/../share/nmap

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 0.70 seconds

이런식으로 해당 포트가 응답이 있는지 먼저 확인해보세요.

nma 사용법 : https://nmap.org/book/port-scanning-tutorial.html

결국 공유기 초기화로 성공했습니다. 답변 주신분들 고맙습니다