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Enable older SSH key exchange methods

When connecting via SSH to older systems who do not support newer ciphers, you will sometimes get the following error:

Unable to negotiate with 10.192.0.47 port 22: no matching key exchange method found. Their offer: diffie-hellman-group14-sha1

To permanently enable support for this cipher, you need to add the following line to either /etc/ssh/ssh_config to enable it for all accounts or ~/.ssh/config for just your account.

Host * 
   KexAlgorithms +diffie-hellman-group14-sha1

You can change Host * to specify a specific IP. Ex: Host 111.111.111.111.

More docs from OpenSSH Legacy Options.

· 2020/07/01 14:17 · 2020/07/02 01:43

Disable the floppy drive module in Linux(Ubuntu)

Sometimes Linux will mistakenly detect a floppy device and create a reference to it because your system does not actually have a floppy drive and you will see errors on the login screen that look similar to blk_update_request: I/O error, dev fd0, sector 0. I find this frequently happens on a VMWare VM. This doesn't affect the system, but it does look annoying to look at on the login console. The fix is to simply to remove and blacklist the floppy kernel module using the following commands …

sudo rmmod floppy
echo "blacklist floppy" | sudo tee /etc/modprobe.d/blacklist-floppy.conf
· 2020/06/22 20:10 · 2020/06/22 20:10

Ubuntu 18.04 to 20.04 Upgrade Notes

  • Upgrading might break your local resolver, DNSMasq. When you issue the command systemctl status dnsmasq, you might get an error that looks something like, dnsmasq: cannot access /etc/dnsmasq.d/lxd: No such file or directory. DNSMasq does not start because it cannot find this file. This file is simply a dangling symlink that needs to be removed, rm /etc/dnsmasq.d/lxd.
  • Upgrading a VM might give you multipath errors in /var/log/syslog:

    VMWare does not pass information needed by udev. To fix this, go to your VM SettingsVM Options tab → AdvancedEDIT CONFIGURATION.

    Add the parameter, disk.EnableUUID and set the value to TRUE. The VM must be powered off to add a new parameter. Reboot your system again and you should no longer receive these errors.
· 2020/04/27 08:02 · 2020/06/22 22:37

Fix DNS after upgrading to Ubuntu Server 20.04

The way DNS is configured in Ubuntu has become overly complicated in the last few versions. Instead of configuring /etc/network/interfaces, it is now configured using Netplan. But sometimes that doesn't even work because DNS is ultimately controlled by systemd-resolv. systemd-resolv generates /etc/resolv.conf and the default stub DNS uses a local resolver to resolve DNS hostnames. For some reason, after upgrading to Ubuntu 20.04 from 18.04, the local resolver was not started or installed. To fix this, you can't just edit /etc/resolv.conf, you must add your custom DNS servers in /etc/resolvconf/resolv.conf.d/head shown in the image below.

Restart the system and your custom DNS servers should stick.

· 2020/04/27 04:36 · 2020/04/27 04:36

Disable IPV6 in Ubuntu 18.04

IPV6 sometimes break DNS resolution in Ubuntu 18.04. Follow the steps below to disable and verify that IPV6 is disabled in Ubuntu.

Edit /etc/sysctl.conf and add the following lines to the end of the file …

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Save the file and issue the following command to force Ubuntu to reload the file.

sysctl -p

To verify that the new configuration has been applied, you can issue the next command.

cat /proc/sys/net/ipv6/conf/all/disable_ipv6

You should receive a result of 1 if it was successfully applied and 0 if it failed.

· 2020/04/12 10:32 · 2020/04/12 10:33

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