DTail is a distributed DevOps tool for tailing, grepping, catting logs and other text files on many remote machines at once.

View the Project on GitHub

Quick Starting Guide

This is the quick starting guide. For a more sustainable setup involving creating a background service via systemd, recommendations about automation via Jenkins and Puppet and health monitoring via Nagios, please follow the Installation Guide.

This guide assumes that you know how to generate and configure a public/private SSH key pair for secure authorization and shell access. For more information, please have a look at the OpenSSH documentation of your distribution.

Install it

To compile and install all DTail binaries directly from GitHub run:

% for cmd in dcat dgrep dmap dtail dserver dtailhealth; do
    go get github.com/mimecast/dtail/cmd/$cmd;

It produces the following executables in $GOPATH/bin:

Start DTail server

Copy the dserver binary to the remote server machines of your choice (e.g. serv-001.lan.example.org and serv-002.lan.example.org) and start it on each of the servers as follows:

❯ ./dserver --logger Stdout --logLevel debug --bindAddress $(hostname) --port 2222
DTail 4.0.0 Protocol 4 Have a lot of fun!
INFO|20211027-102513|Creating server|DTail 4.0.0-RC2 Protocol 4 Have a lot of fun!
INFO|20211027-102513|Reading private server RSA host key from file|./ssh_host_key
INFO|20211027-102513|Starting server
INFO|20211027-102513|Binding server|X.Y.Z.W:2222
INFO|20211027-102513|Starting continuous job runner after 10s
DEBUG|20211027-102513|Starting listener loop
INFO|20211027-102513|Starting scheduled job runner after 10s

dserver is now listening on TCP port 2222 and waiting for incoming connections. All SSH keys listed in ~/.ssh/authorized_keys are now respected by the DTail server for authorization.

Setup DTail client

Setup SSH

Ensure that your public SSH key is listed in ~/.ssh/authorized_keys on all server machines involved. The private SSH key counterpart should preferably stay on your Laptop or workstation in ~/.ssh/id_rsa or ~/.ssh/id_dsa.

DTail relies on SSH for secure authentication and communication. You can either use an SSH Agent or a private SSH key file directly.

SSH Agent

The clients (all client binaries such as dtail, dgrep and so on…) communicate with an auth backend via the SSH auth socket. The SSH auth socket is configured via the environment variable SSH_AUTH_SOCK which usually points to ~/.ssh/ssh_auth_socket or similar (depending on your configuration, it may also point to other auth backends such as GPG Agent, in which case SSH_AUTH_SOCK would point to ~/.gnupg/S.gpg-agent.ssh or similar).

Usually you would use the SSH Auth Agent. For this the private SSH key has to be registered at the SSH Agent:

% ssh-add ~/.ssh/id_rsa
Enter passphrase for ~/.ssh/id_rsa: **********
Identity added: ~/.ssh/id_rsa (~/.ssh/id_rsa)

To test whether SSH is set up correctly, you should be able to SSH into the servers with the OpenSSH client and your private SSH key through the SSH Agent without entering the private key’s passphrase. The following assumes to have an OpenSSH server running on serv-001.lan.example.org and an OpenSSH client installed on your laptop or workstation. Please notice that DTail does not require to have an OpenSSH infrastructure set up, but DTail uses by default the same public/private key file paths as OpenSSH. OpenSSH can be of great help to verify that the SSH keys are configured correctly:

workstation01 ~ % ssh serv-001.lan.example.org
serv-001 ~ %
serv-001 ~ % exit
workstation01 ~ %

Please consult the OpenSSH documentation of your distribution if the test above does not work for you.

SSH Private Key file

As an alternative to using an SSH Agent, an SSH private key file can be used directly. Just add the argument --key ~/.ssh/id_rsa (pointing to your private key) to the DTail client. This currently does not work with password-protected keys. Use the SSH Agent method instead, in case your key comes with a password (recommended).

Run DTail client

Now it is time to connect to the DTail servers through the DTail client:

% dtail --servers serv-001.lan.example.org,server-002.lan.example.org --files "/var/log/service/*.log"
CLIENT|workstation01|INFO|Launching client|tail|DTail 4.0.0
CLIENT|workstation01|INFO|Initiating base client
CLIENT|workstation01|INFO|Added SSH Agent to list of auth methods
CLIENT|workstation01|INFO|Deduped server list|1|1
CLIENT|workstation01|WARN|Encountered unknown host|{serv-002.lan.example.org:2222 0xc000146450 0xc00014a2f0 [serv-002.lan.example.org]:2222 ssh-rsa AAAA....
CLIENT|workstation01|WARN|Encountered unknown host|{serv-001.lan.example.org:2222 0xc0001ff450 0xc00ee4a2f0 [serv-001.lan.example.org]:2222 ssh-rsa AAAA....
Encountered 2 unknown hosts: 'serv-002.lan.example.org:2222 serv-001.lan.example.org:2222'
Do you want to trust these hosts?? (y=yes,a=all,n=no,d=details): y
CLIENT|workstation01|INFO|Added hosts to known hosts file|~/.ssh/known_hosts

Have a look here for more usage examples.