67
votes
Optimal value for Nginx worker_connections
Let's take the pragmatic approach.
All these limits are things that were hardcoded and designed in the past century when hardware was slow and expensive. We're in 2016 now, an average wall-mart ...
- 2,829
60
votes
I accidentaly forbid SSH connection to a remote server... What's next?
There are several alternatives:
See if they have IPMI / "KVM" / console access to the server which lets you control it as if you had a physical keyboard plugged into it.
If they don't offer that, see ...
- 973
47
votes
I accidentaly forbid SSH connection to a remote server... What's next?
If you have not yet saved the IPtables rule, you can reboot server on VPS (if available) and the rule should disappear.
- 1,414
34
votes
RDP fakeout when connectiong: does nothing, no error
I've encountered this type of behavior several times so far with Windows 8/8.1 or Server 2012 machines when they've been rebooted and have a lot of updates to install. For whatever reason it appears ...
- 821
30
votes
I accidentaly forbid SSH connection to a remote server... What's next?
This is what human-staffed help lines are for. Call the service provider, and have one of their operators remove the rule for you.
- 301
26
votes
Optimal value for Nginx worker_connections
ulimit -a will tell you how many open files your system allows a process to use.
Also, net.ipv4.ip_local_port_range sets the total range of sockets to enable per IP.
So, your worker_connections ...
- 1,700
26
votes
Accepted
What causes SSH error: kex_exchange_identification: Connection closed by remote host?
Weirdly, none actually try to authenticate to open a session.
Some spiders and services like Shodan scans public ipv4 addresses for open services, e.g. salt masters, ftp servers, RDPs, and also SSH ...
- 2,536
15
votes
Accepted
Why are connections in FIN_WAIT2 state not closed by the Linux kernel?
The kernel timeout only applies if the connection is orphaned. If the connection is still attached to a socket, the program that owns that socket is responsible for timing out the shutdown of the ...
- 31.4k
14
votes
When using nmcli, what is considered a device, an interface and a connection? What's the difference?
A "network device" (in the context of a computer) typically refers to a piece of hardware - the network interface card (NIC). Once upon a time, back when dinosaurs roamed the internet and lots of ...
- 53.6k
13
votes
Accepted
What does ConnectTimeout in ssh_config mean?
man ssh_config
/ConnectTimeout
ConnectTimeout
Specifies the timeout (in seconds) used when connecting to the SSH server, instead of using the default system TCP timeout. This timeout is applied both ...
- 115k
12
votes
Is ARP Connection oriented or connectionless?
ARP Connection oriented or connectionless?
Connectionless - it's just a request and a response (or a broadcast just letting everyone know about something).
It uses TCP
It doesn't use TCP - TCP is ...
- 114k
12
votes
Siege: descriptor table full sock.c:119: Too many open files
To solve this problem for myself, I had to adjust the OS "ulimit" setting:
ulimit -a -- Check current setting
ulimit -n 10000 -- Edit setting value
Source: https://bugs.debian.org/cgi-bin/bugreport....
- 221
11
votes
RDP fakeout when connectiong: does nothing, no error
IT has been my experience that when you can authenticate but it does not launch the desktop, the remote server is installing updates or is in the middle of building the desktop environment. give it a ...
- 111
9
votes
How to intentionally cause ssh root connection refused
You can't do that.
Your server has no way of knowing what user the remote connection will try to login as, until after it has already connected!
You should consider using fail2ban to block repeated ...
- 240k
8
votes
wget ftp connection failing after PASV command
Another way is to avoid the passive mode, add --no-passive argument in your wget command can do it.
wget -r --no-passive --no-parent ftp://account:<password>@<ip address>/folder/ -P /root
- 181
8
votes
Accepted
After using killall -u root, I am unable to access server and all websites are down
From the killall(1) man page
killall sends a signal to all processes running any of the specified commands. If no signal name is specified, SIGTERM is sent.
...
-u, --user
Kill only ...
- 115k
8
votes
Accepted
Opening 1 million connections maxes out at 469K
Not necessarily an answer but too big to put in a comment.
tcp_mem (since Linux 2.4)
This is a vector of 3 integers: [low, pressure, high]. These bounds, measured in units of the system page ...
- 23.1k
7
votes
What causes SSH error: kex_exchange_identification: Connection closed by remote host?
I've just had this exact issue, and the cause was that I had a port translation happening internally to the load balancer, meaning that my ssh connections were reaching the host on port 80 instead of ...
- 285
5
votes
"ssh root@server" hangs forever
I had the same issue and used the Linux "timeout" to kill a hanging scp session.
timeout -s 9 1h command command_arguments
Will send a kill -9 if the command takes over an hour.
FYI the ...
- 172
5
votes
What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?
If a session does not exist for the source/destination pair, the packet will not be accepted by B. In the case of a SYN-ACK packet, B will reply with a RST (reset) packet, telling the server that no ...
- 151
5
votes
better alternative for tcp_syncookies in linux
Ubuntu 10.04 has default "sysctl.d/10-network-security.conf" setting below:
# Turn on SYN-flood protections. Starting with 2.6.26, there is no loss
# of TCP functionality/features under normal ...
- 2,300
5
votes
Accepted
AWS connect to private subnet instance without going through NAT
if you want to ssh your instance without NAT, it has to be reachable from your network (where your laptop is).
thus I see two solutions:
set an elastic IP to your instance + internet gateway/route to ...
- 616
5
votes
Accepted
Running nginx on AWS is sending back 'ERR_CONNECTION_TIMED_OUT' responses
Configure a security group for the instance which allows inbound tcp 8080. Also ensure a local firewall (iptables, ufw, firewalld or similar) on the instance isn't blocking the traffic.
- 686
4
votes
ssh tunnel refusing connections with "channel 2: open failed"
For me adding leading ":" works so command in your case would look like this:
ssh -L :7000:localhost:7000 user@host -N -v
- 295
4
votes
NIC seems slow, even on 100Mb/s full duplex
As Rex mentioned, the difference there is in bits versus bytes. MB is megabytes, and Mb is megabits. Network speeds are almost always measured in bits. The 10 MB/s performance you're seeing is ...
- 75
4
votes
better alternative for tcp_syncookies in linux
Apparently, tcp_syncookies introduces more benefits than disadvantages.
Instead of the typical speculation on random blogs, perhaps we could consult "the source":
With the updates for IPv6 and ...
- 140
4
votes
Best ways to establish connectivity at each layer of OSI model
Layer 2 requires layer 1 and layer 3 requires layer 2. Everything above that requires a functioning transport layer (3) and therefore tests above that are application specific and will vary between ...
- 991
4
votes
Accepted
Best ways to establish connectivity at each layer of OSI model
If you are debugging connectivity(Layer 3) you need ping and traceroute.
If you want to check open ports you need tcptraceroute(Layer 4 TCP) or nmap (Layer 4 TCP/UDP), but it's pretty hard to debug ...
- 1,579
3
votes
ssh tunnel refusing connections with "channel 2: open failed"
I encountered this error when I was forwarding ports with a full domain name instead of localhost:
ssh -L 5900:host.name.com:5900 x11vnc
The port was being opened only for localhost, so to accept ...
- 131
3
votes
Able to connect by SSH, but not x2go
Encountered the same problem from Windows could not connect to remote linux client with SSH Key. Even Auto Login with Pageant running from PuTTY directly or running the included X2GO Pageant would ...
- 31
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