Membalas pertanyaan:
- YA, downgrade diperlukan agar nc dapat mendengarkan. dan untuk komentar lainnya:
a) -p tidak seharusnya digunakan saat dalam mode mendengarkan. dari nc manpage:
-l Digunakan untuk menentukan bahwa nc harus mendengarkan koneksi yang masuk daripada memulai koneksi ke host jarak jauh. Ini adalah kesalahan untuk menggunakan opsi ini dalam hubungannya dengan opsi -p, -s, atau -z.
b) downgrade dapat dilakukan dalam satu langkah, yum perintah downgrade bekerja dengan url ke paket:
$ rpm -q nc
nc-1.84-24.el6.x86_64
$ nc -l 12345 #Although the syntax is correct, the command fails
nc: Protocol not available
$ nc -l -p 12345 #attempt to run with incorrect syntax
usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
$ sudo yum downgrade http://vault.centos.org/6.6/os/x86_64/Packages/nc-1.84-22.el6.x86_64.rpm #shortcut to downgrade
...
Setting up Downgrade Process
nc-1.84-22.el6.x86_64.rpm | 57 kB 00:00
Examining /var/tmp/yum-root-Iq4yc7/nc-1.84-22.el6.x86_64.rpm: nc-1.84-22.el6.x86_64
Resolving Dependencies
--> Running transaction check
---> Package nc.x86_64 0:1.84-22.el6 will be a downgrade
---> Package nc.x86_64 0:1.84-24.el6 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
==============================================================================================================
Package Arch Version Repository Size
==============================================================================================================
Downgrading:
nc x86_64 1.84-22.el6 /nc-1.84-22.el6.x86_64 109 k
Transaction Summary
==============================================================================================================
Downgrade 1 Package(s)
Total size: 109 k
Is this ok [y/N]: y
...
Removed:
nc.x86_64 0:1.84-24.el6
Installed:
nc.x86_64 0:1.84-22.el6
Complete!
$ nc -l -p 12345 #attempt to run with incorrect syntax
usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
$ nc -l 12345 # try to listen again
^C
$#nc successully opens a socket on 12345. had to stop it with ctrl+C