# Runroot¶

## Preface¶

Runroot is a powerful feature to detect and define layout at runtime. This document helps to guide through how runroot works. For management and setup of runroots, please refer to appendices/command-line/traffic_layout.en

Runroot is a replacing approach for the previous TS_ROOT logic. TS_ROOT is based on replacing a compile-time package install root location. Layouts for many systems have data location that are absolute paths that are defined without $PREFIX variable. So, the current logic is difficult to follow and not consistent between trafficserver programs. Furthermore, it is not easy to modify subdirectory locations. So, we have the runroot which makes ATS easier to use, develop and deploy. ## Main logic¶ Everything in runroot will go through the class:Layout class and all the layout is defined by a single YAML file: runroot.yaml. Work flow: 1. Command line option --run-root 2. $TS_RUNROOT Environment variable
3. Look in current directory and look up N (default 4) directories for runroot.yaml
4. Look in executable directory and look up N directories for runroot.yaml.
5. \$TS_ROOT Environment Variable
6. Compiler defaults in layout class

Right now, the following programs are integrated with the runroot logic: traffic_server, traffic_manager, traffic_ctl, traffic_layout, traffic_crashlog, traffic_logcat, traffic_logstat.

## The YAML file¶

The runroot file (runroot.yaml) can be placed at any location in the filesystem and still be used to define the locations for required Traffic Server files. So we can run traffic_server, for example, by traffic_server --run-root=/some/directory/runroot.yaml.

Below is an example of runroot.yaml.

prefix: /home/myname/runroot
exec_prefix: /home/myname/runroot
bindir: /home/myname/runroot/bin
sbindir: /home/myname/runroot/bin
sysconfdir: /etc/trafficserver
includedir: /home/myname/runroot/include
libdir: /home/myname/runroot/lib
libexecdir: /libexec/trafficserver
localstatedir: /var
runtimedir: /var/trafficserver
logdir: /home/myname/runroot/logdir
cachedir: /var/trafficserver


The path can be both relative or absolute. We can define wherever we want the directory to be. All the items we need to put into runroot.yaml are shown above and the entries can be optional. For example, if sysconfdir is not in the file, runroot will set the sysconfidir, at runtime, to be the default built time sysconfdir concatenated with the prefix.

## Runroot management¶

We can create, remove and verify runroot using traffic_layout program. It is fully documented in the appendices.

## Guide for development¶

Basic runroot functionality is handled in runroot.cc and runroot.h of lib/tscore. runroot_handler() and argparser_runroot_handler() are the main methods for the runroot. The Layout class will then get the global variable from runroot.cc to set up the directories properly.

## Issue or bug¶

This functionality should be stable and if there is any issue or bug, please report it on the GitHub and @chitianhao.