It seems highly implausible, even ridiculous, to me.
I login by SSH to the CentOS server. I FTP to another server and begin a large file transfer out (uploading to other server).
After some time (usually about 3 - 30 seconds), I get kicked off SSH.
I have never had a problem on any other server where I got kicked out of SSH because of FTP bandwidth.
root@my_server [/home/my_folder/public_html]# ftp xx.xxx.xx.xx Connected to xx.xxx.xx.xx. 220 (vsFTPd 2.3.5) 530 Please login with USER and PASS. 530 Please login with USER and PASS. KERBEROS_V4 rejected as an authentication type Name (xx.xxx.xx.xx:root): buttle_butkus 331 Please specify the password. Password: 230 Login successful. Remote system type is UNIX. Using binary mode to transfer files. ftp> cd speedtest 250 Directory successfully changed. ftp> 2gb_file.tar.gz local: 2gb_file.tar.gz remote: 2gb_file.tar.gz 227 Entering Passive Mode (xx,xxx,xx,xx,xxx,xxx). Connection closed by host Disconnected
Server hosting company said that it's because "all of the bandwidth is being used by FTP". I have never heard of such a thing, but before I tell them they're crazy I wanted to ask the experts here.
They also suggested I change the
UserBandwidth option in pure-ftpd.conf to 15. That's 15 kilobytes/s on a 100mbps connection. I guess I need to leave about 99.9mbps for SSH??
I did change it, but it didn't affect upload speed anyway (still very fast). Perhaps the setting only affects outside users logging into the server by FTP. I'm logged in by SSH, and FTP-ing out.
EDIT: Adding part of tshark captured traffic (ip addresses partially obscured):
544 111.343171 xx.xx.195.90 -> xx.xx.230.39 SSH [TCP Retransmission] Encrypted response packet len=60 545 117.486826 xx.xx.195.90 -> xx.xx.230.39 SSH [TCP Retransmission] Encrypted response packet len=60 546 125.464960 xx.xx.94.90 -> xx.xx.195.90 TCP [TCP Previous segment lost] ssh > csd-monitor [SYN, ACK] Seq=498204672 Ack=2219931860 Win=8192 [TCP CHECKSUM INC ORRECT] Len=0 547 129.774351 xx.xx.195.90 -> xx.xx.230.39 SSH [TCP Retransmission] Encrypted response packet len=60 548 154.348760 xx.xx.195.90 -> xx.xx.230.39 SSH [TCP Retransmission] Encrypted response packet len=60 549 203.497887 xx.xx.195.90 -> xx.xx.230.39 SSH [TCP Retransmission] Encrypted response packet len=60 550 279.243718 xx.xx.195.90 -> xx.xx.230.39 SSH Encrypted response packet len=9 52