Fix capistrano errors: "no such file to load -- net/ssh/authentication/agent/socket" or "uninitialized constant Net::SSH::KnownHosts::SUPPORTED_TYPE"

For example if you use rvm and get this message:

ERROR:  Loading command: install (LoadError)
    no such file to load -- zlib
ERROR:  While executing gem ... (NameError)
    uninitialized constant Gem::Commands::InstallCommand

...

I got this error after upgrading Ruby from 2.4.5 to 2.6.4 when I opened the Rails console - rails server still worked.

Running via Spring preloader in process 14679
Loading development environment (Rails 5.2.2.1)
Traceback (most recent call...

Install libreadline:

sudo apt-get install libreadline-dev

Reinstall the ruby and tell rvm where to find readline

rvm reinstall 1.8.7 --with-readline-dir=/usr/include/readline

Make sure you get a huge cup of tea before running the com...

Today, I ran into trouble on a fairly fresh installed VM, running Ubuntu. I tried to bundle install and got this stacktrace:

Fetching gem metadata from https://rubygems.org/.Unfortunately, a fatal error has occurred. Please see the Bund...

If you're on Ubuntu:

sudo apt-get install ruby-dev

On other platforms: Look for a package containing ruby header files. On Red Hat that's "ruby-devel" likely.

If you get this error (probably because you want to load some modules):

# modprobe xt_comment
FATAL: Could not load /lib/modules/3.2.0-40-generic/modules.dep: No such file or directory

The reason could be that apt-get autoremove al...

This error can be caused by the mysql2 gem under mysterious circumstances. You need to remove it with gem uninstall mysql2 and then reinstall it (or just run bundle).

gem pristine mysql2 will not be enough.

If you get a message like this:

Jan 21 13:42:38 foobar syslogd: /var/log/authlog : no such file or directory

But you are sure the file exists and it have the correct permissions:

# example for Solaris 9
-rw-r--r-- 1 root sys 8,0...

You are getting when connecting via SSH or deploying with Capistrano (which uses SSH):

Too many authentication failures for username

This is caused by having too many SSH keys added to your keyring or ssh-agent. Your ssh-agent will throw all...

If you encounter above mentioned failiure message after installing the ruby-debug gem then you have to explicitly require linecache version 0.43 in your Gemfile.

gem 'ruby-debug'
gem 'linecache', '=0.43'