当我执行以下操作时，我在 centos 6 中遇到端口转发问题：
ssh -v -R root@hostname:19999:localhost:22 root@hotname
我收到此警告：
Warning: remote port forwarding failed for listen port 19999
ssh 会话启动，但我不能将其用作隧道，完整的输出如下：
OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to hostname [ip.ip.ip.ip] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/identity type -1
debug1: identity file /root/.ssh/identity-cert type -1
debug1: identity file /root/.ssh/id_rsa type -1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1 …