centos下什么是nc

yum?install?nc?-y

#?nc?--help? Ncat?7.50?(?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 ??-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 ??????--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>??Specify?address?of?host?to?proxy?through ??????--proxy-type?<type>????Specify?proxy?type?("http"?or?"socks4"?or?"socks5") ??????--proxy-auth?<auth>????Authenticate?with?HTTP?or?SOCKS?proxy?server ??????--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 ??????--version??????????????Display?Ncat's?version?information?and?exit</auth></type></addr></time></time></filename></filename></time></n></n></n></filename></command></command>

nc?-l?80

nc?-lu?80

>?#?netstat?-tunlp Active?Internet?connections?(only?servers) Proto?Recv-Q?Send-Q?Local?Address???Foreign?Address???State??PID/Program?name??? udp????????0??????0?0.0.0.0:80??????0.0.0.0:*????????????????15401/nc