netcat은 네트워크 디버깅, 파일 전송, 포트 스캐닝, 원격 제어 등 다양한 용도로 사용할 수 있습니다.
파일 전송 보안이 중요하다면 scp를 사용하면 됩니다.
redhat 계열 리눅스에서는 SSL을 지원 합니다.
아래 내용은 netcat을 사용해서 대용량 파일 및 디렉토리를 전송하는 과정이다.
debian 리눅스 계열
$ sudo apt install netcat-traditional netcat-openbsd
$ nc -h
OpenBSD netcat (Debian patchlevel 1.226-1ubuntu2)
usage: nc [-46CDdFhklNnrStUuvZz] [-I length] [-i interval] [-M ttl]
[-m minttl] [-O length] [-P proxy_username] [-p source_port]
[-q seconds] [-s sourceaddr] [-T keyword] [-V rtable] [-W recvlimit]
[-w timeout] [-X proxy_protocol] [-x proxy_address[:port]]
[destination] [port]
Command Summary:
-4 Use IPv4
-6 Use IPv6
-b Allow broadcast
-C Send CRLF as line-ending
-D Enable the debug socket option
-d Detach from stdin
-F Pass socket fd
-h This help text
-I length TCP receive buffer length
-i interval Delay interval for lines sent, ports scanned
-k Keep inbound sockets open for multiple connects
-l Listen mode, for inbound connects
-M ttl Outgoing TTL / Hop Limit
-m minttl Minimum incoming TTL / Hop Limit
-N Shutdown the network socket after EOF on stdin
-n Suppress name/port resolutions
-O length TCP send buffer length
-P proxyuser Username for proxy authentication
-p port Specify local port for remote connects
-q secs quit after EOF on stdin and delay of secs
-r Randomize remote ports
-S Enable the TCP MD5 signature option
-s sourceaddr Local source address
-T keyword TOS value
-t Answer TELNET negotiation
-U Use UNIX domain socket
-u UDP mode
-V rtable Specify alternate routing table
-v Verbose
-W recvlimit Terminate after receiving a number of packets
-w timeout Timeout for connects and final net reads
-X proto Proxy protocol: "4", "5" (SOCKS) or "connect"
-x addr[:port] Specify proxy address and port
-Z DCCP mode
-z Zero-I/O mode [used for scanning]
Port numbers can be individual or ranges: lo-hi [inclusive]
방화벽 포트 오픈
$ ufw allow 2121
redhat 리눅스 계열
# yum install nc
$ nc --help
Ncat 7.92 ( https://nmap.org/ncat )
Usage: ncat [options] [hostname] [port]
Options taking a time assume seconds. Append 'ms' for milliseconds,
's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
-4 Use IPv4 only
-6 Use IPv6 only
-U, --unixsock Use Unix domain sockets only
--vsock Use vsock sockets only
-C, --crlf Use CRLF for EOL sequence
-c, --sh-exec <command> Executes the given command via /bin/sh
-e, --exec <command> Executes the given command
--lua-exec <filename> Executes the given Lua script
-g hop1[,hop2,...] Loose source routing hop points (8 max)
-G <n> Loose source routing hop pointer (4, 8, 12, ...)
-m, --max-conns <n> Maximum <n> simultaneous connections
-h, --help Display this help screen
-d, --delay <time> Wait between read/writes
-o, --output <filename> Dump session data to a file
-x, --hex-dump <filename> Dump session data as hex to a file
-i, --idle-timeout <time> Idle read/write timeout
-p, --source-port port Specify source port to use
-s, --source addr Specify source address to use (doesn't affect -l)
-l, --listen Bind and listen for incoming connections
-k, --keep-open Accept multiple connections in listen mode
-n, --nodns Do not resolve hostnames via DNS
-t, --telnet Answer Telnet negotiations
-u, --udp Use UDP instead of default TCP
--sctp Use SCTP instead of default TCP
-v, --verbose Set verbosity level (can be used several times)
-w, --wait <time> Connect timeout
-z Zero-I/O mode, report connection status only
--append-output Append rather than clobber specified output files
--send-only Only send data, ignoring received; quit on EOF
--recv-only Only receive data, never send anything
--no-shutdown Continue half-duplex when receiving EOF on stdin
--allow Allow only given hosts to connect to Ncat
--allowfile A file of hosts allowed to connect to Ncat
--deny Deny given hosts from connecting to Ncat
--denyfile A file of hosts denied from connecting to Ncat
--broker Enable Ncat's connection brokering mode
--chat Start a simple Ncat chat server
--proxy <addr[:port]> Specify address of host to proxy through
--proxy-type <type> Specify proxy type ("http", "socks4", "socks5")
--proxy-auth <auth> Authenticate with HTTP or SOCKS proxy server
--proxy-dns <type> Specify where to resolve proxy destination
--ssl Connect or listen with SSL
--ssl-cert Specify SSL certificate file (PEM) for listening
--ssl-key Specify SSL private key (PEM) for listening
--ssl-verify Verify trust and domain name of certificates
--ssl-trustfile PEM file containing trusted SSL certificates
--ssl-ciphers Cipherlist containing SSL ciphers to use
--ssl-servername Request distinct server name (SNI)
--ssl-alpn ALPN protocol list to use
--version Display Ncat's version information and exit
See the ncat(1) manpage for full options, descriptions and usage examples
방화벽 포트 오픈
$ firewall-cmd --permanent --zone=public --add-port=2121/tcp
$ firewall-cmd --reload
서버 파일 수신 대기
$ nc -vl 2121 | tar zxv
클라이언트 디렉토리 송신
## debian 계열
$ tar czp /data/mariadb/backup/full | nc -N serverhost 2121
## redhat 계열
$ tar czp /data/mariadb/backup/full | nc serverhost 2121
클라이언트 파일 송신
## debian 계열
$ tar czf - /data/mariadb/backup/inc/info.file | nc -N 223.13x.xxx.xxx 2121
## redhat 계열
$ tar czf - /data/mariadb/backup/inc/info.file | nc 223.13x.xxx.xxx 2121
파일 및 디렉토리 전송이 완료되면 서버 측 netcat 이 종료된다.