How can I tail a remote file?

Question

I am trying to find a good way to tail a file on a remote host. This is on an internal network of Linux machines. The requirements are:

1. Must be well behaved (no extra process laying around, or continuing output)

2. Cannot require someone's pet Perl module.

3. Can be invoked through Perl.

4. If possible, doesn't require a custom built script or utility on the remote machine (regular linux utilities are fine)

The solutions I have tried are generally of this sort

ssh remotemachine -f <some command>

"some command" has been:

tail -f logfile

Basic tail doesn't work because the remote process continues to write output to the terminal after the local ssh process dies.

$socket = IO:Socket::INET->new(...);
$pid = fork();
if(!$pid)
{
  exec("ssh $host -f '<script which connects to socket and writes>'");
  exit;
}

$client = $socket->accept;
while(<$client>)
{
  print $_;
}

This works better because there is no output to the screen after the local process exits but the remote process doesn't figure out that its socket is down and it lives on indefinitely.

Answer 1

There is File::Tail. Don't know if it helps?

Answer 2

Some ideas:

• You could mount it over NFS or CIFS, and then use File::Tail.
• You could use one of Perl's SSH modules (there are a number of them), combined with tail -f.

Answer 3

rsync://[USER@]HOST[:PORT]/SRC... [DEST] | tail [DEST] ?

Answer 4

netcat should do it for you.

Answer 5

Have you tried

ssh -t remotemachine <some command>

instead of

-f

?

Answer 6

Someone suggested using nc (netcat). This solution does work but is less ideal than just using ssh -t. The biggest problem is that you have to use nc on both sides of the connection and need to do some port discovery on the local machine to find a suitable port over which to connect. Here is the adaptation of the above code to use netcat:

$pid = fork();
if(!$pid)
{
  exec("ssh $host -f 'tail -f $filename |nc $localhost $port'");
  exit;
}

exec("nc -l -p $port");

Answer 7

You could try Survlog Its OS X only though.