How to fix "SSH is responding very slowly" ?

When we try to connect to other nodes in the cluster, SSH is responding very slowly. this is usually a dns issue, so we turn it off. For more information, please refer to: https://www.serverpronto.com/accounts/knowledgebase.php?action=displayarticle&id=16 

Solution

To test this issue, use:

1 2 arp -a # To check a lookup arp -an # To check for a reverse look up

To solve the issue, either update /etc/resolv.conf with the proper nameserver ip addresses or follow the steps below.

Update the ssh config:

1 sudo /etc/ssh/sshd_config

Find #useDNS yes

Replace with useDNS no

Restart the sshd service:

1 service sshd restart

ssh connection speed test

Test ssh connection speed

#!/bin/bash
# scp-speed-test.sh

# Usage:
#   ./scp-speed-test.sh user@hostname [test file size in kBs]
#

ssh_server=$1
test_file=".scp-test-file"

# Optional: user specified test file size in kBs
if test -z "$2"
then
  # default size is 10kB ~ 10mB
  test_size="10000"
else
  test_size=$2
fi


# generate a 10000kB file of all zeros
echo "Generating $test_size kB test file..."
`dd if=/dev/zero of=$test_file bs=$(echo "$test_size*1024" | bc) \
  count=1 &> /dev/null`

# upload test
echo "Testing upload to $ssh_server..."
up_speed=`scp -v $test_file $ssh_server:$test_file 2>&1 | \
  grep "Bytes per second" | \
  sed "s/^[^0-9]*\([0-9.]*\)[^0-9]*\([0-9.]*\).*$/\1/g"`
up_speed=`echo "($up_speed*0.0009765625*100.0+0.5)/1*0.01" | bc`

# download test
echo "Testing download to $ssh_server..."
down_speed=`scp -v $ssh_server:$test_file $test_file 2>&1 | \
  grep "Bytes per second" | \
  sed "s/^[^0-9]*\([0-9.]*\)[^0-9]*\([0-9.]*\).*$/\2/g"`
down_speed=`echo "($down_speed*0.0009765625*100.0+0.5)/1*0.01" | bc`

# clean up
echo "Removing test file on $ssh_server..."
`ssh $ssh_server "rm $test_file"`
echo "Removing test file locally..."
`rm $test_file`

# print result
echo ""
echo "Upload speed:   $up_speed kB/s"
echo "Download speed: $down_speed kB/s"