nf_conntrack: table full, dropping packet

On a CentOS server, i get following error in /var/log/messages

Jan 17 03:40:02 ss1 kernel: nf_conntrack: table full, dropping packet
Jan 17 03:40:03 ss1 kernel: nf_conntrack: table full, dropping packet
Jan 17 03:40:03 ss1 kernel: nf_conntrack: table full, dropping packet
Jan 17 03:40:03 ss1 kernel: nf_conntrack: table full, dropping packet
Jan 17 03:40:03 ss1 kernel: nf_conntrack: table full, dropping packet
Jan 17 03:40:03 ss1 kernel: nf_conntrack: table full, dropping packet

This is because the server is getting too much connections. This can be due to a busy server or DDoS attack.

if you traffic is legit, you can increase maximum connection tracking.

To see current value, run

To set value, run

Change 64000 with your desired value.

You can also use sysctl, for example

To set value, run

To make it permanent, edit

Add

Now run

See sysctl

screen

screen allow you to run commands in remote server even after you disconnect.

disconnect from a session

You can just close terminal, program running inside screen will keep running.

Other solution is press

CTRL + A, then press CTRIL +D in quick succession.

Change SSH Key Passphrase

To change SSH key passphrase, run

Example

See ssh-keygen

lsblk

lsblk list all block level devices available on your system.

Example

See fs

Add Server to R1Soft Server Backup Manager

After installing r1soft backup agent, you need to add the server to R1Soft Server Backup Manager SE.

Click on “Protected Machines” link on left side menu.

Click on “New Machine” button.

r1soft backup

On this page, enter following details “Machine Name” and “Hostname / IP”. I used host name as Machine Name. Then used IP address. I don’t enable Encryption, you can enable it for added security.

Click Save button.

Now login to server where Backup Agent is installed (Protected Machine) and run

Example

Now verify key is added with command

Next, you need to Configure Server Backup in R1Soft Backup Manager