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

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DTail Installation Guide

The following installation guide has been tested successfully on CentOS 7. You may need to adjust accordingly depending on the distribution you use.

Compile it

Please check the Quick Starting Guide for instructions on compiling DTail. It is recommended to automate the build process via your build pipeline (e.g. produce a deployable (.rpm, .deb, …) via Jenkins). You don’t have to use go get... to compile and install the binaries. You can also clone the repository and use make instead.

Linux ACL support

This is optional, but it gives you better security. On Linux, you have the option to compile dserver with File System Access Control List support. For that, you need:

1. Install the libacl development library. On RHEL, CentOS and Fedora, it would be

% sudo dnf install libacl-devel -y

2. Enable ACL via a Go build flag

Set the USE_ACL environment variable before invoking the make command.

% export USE_ACL=yes

Alternatively, you could add -tags linuxacl to the Go compiler.

Install it

It is recommended to automate all the installation process outlined here. You could use a configuration management system such as Puppet, Chef or Ansible. However, that relies heavily on how your infrastructure is managed and is out of scope of this documentation.

  1. The dserver binary has to be installed on all machines (server boxes) involved. A good location for the binary would be /usr/local/bin/dserver with permissions set as follows:
% sudo chown root:root /usr/local/bin/dserver
% sudo chmod 0755 /usr/local/bin/dserver
  1. Create the dserver run user and group. The user could look like this:
% sudo adduser dserver
% id dserver
uid=1001(dserver) 1001=670(dserver) groups=1001(dserver)
  1. Create the required file system structure and set the correct permissions:
% sudo mkdir -p /etc/dserver /var/run/dserver
% sudo chown -R dserver:dserver /var/run/dserver
  1. Install the dtail.json config to /etc/dserver/dtail.json. An example can be found here.
% sudo mkdir /etc/dserver
% curl https://raw.githubusercontent.com/mimecast/dtail/master/samples/dtail.json.sample |
    sudo tee /etc/dserver/dtail.json
  1. It is recommended to configure DTail server as a service to systemd. An example unit file for systemd can be found here.
% curl https://raw.githubusercontent.com/mimecast/dtail/master/samples/dserver.service.sample |
    sudo tee /etc/systemd/system/dserver.service
% sudo systemctl daemon-reload
% sudo systemctl enable dserver

Start it

To start the DTail server via systemd run:

% sudo systemctl start dserver
% sudo systemctl status dserver
● dserver.service - DTail server
   Loaded: loaded (/etc/systemd/system/dserver.service; disabled; vendor preset: disabled)
   Active: active (running) since Fri 2019-12-06 13:21:24 GMT; 2s ago
   Main PID: 12296 (dserver)
   Memory: 1.5M
   CGroup: /dserver.slice/dserver.service
     └─12296 /usr/local/bin/dserver -cfg /etc/dserver/dtail.json

    Dec 06 13:21:24 serv-001.lan.example.org systemd[1]: Started DTail server.
    Dec 06 13:21:24 serv-001.lan.example.org dserver[12296]: SERVER|serv-001|INFO|Launching server|server|DTail 1.0.0
    Dec 06 13:21:24 serv-001.lan.example.org dserver[12296]: SERVER|serv-001|INFO|Creating server|DTail 1.0.0
    Dec 06 13:21:24 serv-001.lan.example.org dserver[12296]: SERVER|serv-001|INFO|Reading private server RSA host key from file|cache/ssh_host_key
    Dec 06 13:21:24 serv-001.lan.example.org dserver[12296]: SERVER|serv-001|INFO|Starting server
    Dec 06 13:21:24 serv-001.lan.example.org dserver[12296]: SERVER|serv-001|INFO|Binding server|

Register SSH public keys in DTail server

The DTail server now runs as a systemd service under system user dserver. However, the system user dserver has no permissions to read the SSH public keys from /home/USER/.ssh/authorized_keys. Therefore, no user would be able to establish an SSH session to DTail server. As an alternative path DTail server also checks for public SSH key files in /var/run/dserver/cache/USER.authorized_keys.

It is recommended to execute update_key_cache.sh periodically to update the key cache. In case you manage your public SSH keys via Puppet you could subscribe the script to corresponding module. Or alternatively just configure a cron job or a systemd timer to run every once in a while, e.g. every 30 minutes:

% curl https://raw.githubusercontent.com/mimecast/dtail/master/samples/update_key_cache.sh.sample |
    sudo tee /var/run/dserver/update_key_cache.sh
% sudo chmod 755 /var/run/dserver/update_key_cache.sh
% curl https://raw.githubusercontent.com/mimecast/dtail/master/samples/dserver-update-keycache.service.sample |
    sudo tee /etc/systemd/system/dserver-update-keycache.service
% curl https://raw.githubusercontent.com/mimecast/dtail/master/samples/dserver-update-keycache.timer.sample |
    sudo tee /etc/systemd/system/dserver-update-keycache.timer
% sudo systemctl daemon-reload
% sudo systemctl start dserver-update-keycache.service
% sudo systemctl enable dserver-update-keycache.timer
% sudo systemctl start dserver-update-keycache.timer

Run DTail client

Now you should be able to use DTail client like outlined in the Quick Starting Guide. Also, have a look at the Examples.

Monitor it

To verify that DTail server is up and running and functioning as expected, you should configure the Nagios check check_dserver.sh in your monitoring system. The check has to be executed locally on the server (e.g. via NRPE). How to configure the monitoring system in detail is out of scope of this guide.

% ./check_dserver.sh
OK: DTail SSH Server seems fine