Executing 'tail -f' with Capistrano 3 pipes nothing into output - ruby

Question

I have a Capistrano task that looks like this:
desc "tail log file"
task :tail do
on roles(:app) do
execute "tail -f #{shared_path}/log/#{fetch(:log_file)}.log"
end
end
When I run the task, it proceeds with the blocking tail -f request, but it shows up nothing. I am one hundred percent sure that it simply does not pipe the data somehow (I've verified it - the log file gets updated on the remote) thus it shows nothing. Did I miss something?
The app role is included in the stage config.

Answer 1

Mmmmmmm..., check the permissions in the file system. The user that runs the task should have the permission to read the file.
You can try chmod o+r logfile.log
Here you're giving permissions to read to anybody on the file (Useful for debugging purposes).

Answer 2

I have found a workaround/solution to my problem. I don't remember where I did found the solution, but executing the command rawly by instantiating an ssh connection with a pseudo-tty forced allocation (that's the -t) got it working. That will get the blocking requests like tail -f working. As the man pages say on the -t option:
This can be used to execute arbitrary screen-based programs on a remote machine,
which can be very useful...
def execute_interactively(command)
user = fetch(:user)
port = fetch(:port)
cmd = "ssh -l #{user} #{host} -p #{port} -t 'cd #{deploy_to}/current && #{command}'"
exec cmd
end

Answer 3

You'll need to set the capistrano verbosity level to DEBUG to see any streaming output. I found the solution in the capistrano3-taillog gem; see taillog.cap.
desc "tail log file"
task :tail do
on roles(:app) do
with_verbosity Logger::DEBUG do
execute "tail -f #{shared_path}/log/#{fetch(:log_file)}.log"
end
end
end
def with_verbosity(output_verbosity)
old_verbosity = SSHKit.config.output_verbosity
begin
SSHKit.config.output_verbosity = output_verbosity
yield
ensure
SSHKit.config.output_verbosity = old_verbosity
end
end