# README

Tailon

Tailon is a webapp for looking at and searching through files and streams. In a nutshell, it is a fancy web wrapper around the following commands:

tail -f
tail -f | grep
tail -f | awk
tail -f | sed

What sets tailon apart from other similar projects is:

Fully self-contained executable.
Small footprint. The tailon executable is 2.5MB in size and uses 10MB of RSS.
Responsive and minimal user-interface.

Install

Download a build for your platform from releases or fetch it using go get:

go get -u github.com/gvalkov/tailon-next

A docker image is also available:

docker run --rm gvalkov/tailon --help

Usage

Tailon is a command-line program that spawns a local HTTP server that serves files that you specify. It can be configured from its command-line interface or through the convenience of a toml config file.

To get started, run tailon with the list of files that you wish to monitor:

tailon /var/log/apache/access.log "glob,/var/log/nginx/*"

Tailon can serve single-files, globs or whole directory trees. Tailon’s server-side functionality is summarized entirely in its help message:

Usage: tailon [options] -c <config file>
Usage: tailon [options] <filespec> [<filespec> ...]

Tailon is a webapp for looking at and searching through files and streams.

  -a, --allow-download         allow file downloads (default true)
  -b, --bind string            Listen on the specified address and port (default ":8080")
  -c, --config string
  -h, --help                   Show this help message and exit
  -e, --help-config            Show configuration file help and exit
  -r, --relative-root string   webapp relative root (default "/")

Tailon can be configured through a config file or with command-line flags.

The command-line interface expects one or more filespec arguments, which
specify the files or directories to be served. The expected format is:

  [[glob|dir|file],alias=name,group=name,]<path>

The default filespec is 'file' and points to a single, possibly non-existent
file. The file name in the UI can be overwritten with the 'alias=' specifier.

The 'glob' filespec evaluates to the list of files that match a shell file
name pattern. The pattern is evaluated each time the file list is refreshed.
The 'alias=' specifier overwrites the parent directory of each matched file.

The 'dir' specifier evaluates to all files in a directory.

The "group=" specifier sets the group in which files appear in the file
dropdown of the toolbar.

Example usage:
  tailon file1.txt file2.txt file3.txt
  tailon alias=messages,/var/log/messages "glob:/var/log/*.log"
  tailon -b localhost:8080 -c config.toml

For information on usage through the configuration file, please refer to the
'--help-config' option.

Security

Tailon runs commands on the server it is installed on. While commands that accept a script argument (such as awk, sed and grep) should be invulnerable to shell injection, they may still allow for arbitrary command execution and unrestricted access to the filesystem.

To clarify this point, consider the following input to the sed command:

s/a/b'; cat /etc/secrets

This will result in an error, as tailon does not invoke commands through a shell. On the other hand, the following command is a perfectly valid sed script that has the same effect as the above attempt for shell injection:

r /etc/secrets

The default set of enabled commands - tail, grep and awk - should be safe to use. GNU awk is run in sandbox mode, which prevents scripts from accessing your system, either through the system() builtin or by using input redirection.

By default, tailon is accessible to anyone who knows the server address and port. Basic and digest authentication are under development.

What about the other tailon project.

Tailon-next is a full rewrite of the original tailon with the following goals in mind:

Easier maintenance for the maintainer.
Remove unwanted features and fix poor design choices.
Learn more.

In terms of tech, the following has changed:

Backend from Python+Tornado to Go.
Frontend from a very-custom and specific Typescript solution to a simple ES5 + vue.js (mostly for data-binding).
Simplified asset pipeline (a short Makefile).
Config file is now toml.
Fully self contained