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If you're running TIO on your own server, please read this and update to the latest version.

Setting up Try it Online

What is Try It Online is a web site that started out as a place for hosting solutions to code golf puzzles presented on It can be used by anyone for free to quickly try out and share code snippets, with or without code golf in mind alike, in a big number of practical and recreational programming languages.

Setup Overview

These instructions are written to help set up a new instance of Try It Online.

TIO currently uses 2 domains which are served from its main server. There are also multiple load balanced arena servers, which are accessed from the main server via SSH. The GitHub repositiory for them is

  • Main server split across 2 domains:
    • - serves redirects to For backward compatibility and for more recognizable name.
    • is the web app that enables visitors to test their code online.
  • Arena servers, i.e., servers where the user-supplied code is executed in a sandboxed environment (SELinux). These are accessed by the main server via SSH over a private network.

The main server setup instructions will set up a single server which can act both as main and arena server. You have an option of running the site with arena and main on the same VPS, splitting main and arena to two different VPS, or having more than one arena nodes. TryItOnline currently has two arenas in addition to the main server, which is not use as a public arena. The arena on the current TIO main server is used to test (dry run) language updates before rsyncing them with the two arenas.

The setup makes use of SELinux, support of which varies between different distributions of Linux.

This setup runs on Fedora 26 and was tested on Linode.

It is assumed that you have a freshly provisioned instance(s) on Linode. All scripts are run as root. It might be possible to run the setup on another hosting provider, such as Digital Ocean or Vultr, however minor image differences may require slightly different prep steps, which are not covered here. You will need minimum of 1 GiB of memory in any case.

Domain registration and certificates

In order to setup TIO, you will need the following sub-domains created within your domains. Note that these are the ones that TIO itself uses, yours, obviously will be different:


You will need to provide your domain names to the setup scripts.

Our setup scripts use LetsEncrypt for SSL certificates, which is free of charge. You are welcome to use your own certificates, but you will need to update the setup scripts accordingly. LetsEncrypt uses Certbot for generating SSL certificates and configuring httpd to use them. In order for this to work, the domains that you are going to be use in your setup have to point to the the VM's IP address that you are running the setup scripts on.

Thus, a recommended sequence would be following:

  • Register one or more domains to use with TIO.
  • Provision a TIO main server machine.
  • Point domains (your versions of and to the VM IP.

After that, Certbot will be able to validate the fact that it's you who are controlling these domains, and generate the certificates for you. Note, that LetsEncrypt limits you to 5 sets of certificates per week for each domain combination you use. Thus, if you are going to run the setup scripts multiple times (for testing), it is advisable to tar czf letsencrypt.tar.gz /etc/letsencrypt after the first run of the setup scripts, so that you can reuse these certificates on the next run, and thus avoid hitting the rate limit.

Generating SSH keys

There are three key pairs that is involved in TryItOnline setup:

  • "apache" keypair which is used for authenticating main against arena when Try It Online executes user-supplied code.
  • "root" keypair which is used for authenticating main against arena for rsync, which is kicked off for either initial arena setup or for updating arena from main.
  • "host" keypair which is used in the both cases above to authenticate arena against main.

Note, that main and all arenas will have all three keypairs above. These are in addition to keypairs you may use for your own SSH access to any of the servers.

During setup the apache and the root keypairs will get generated if not provided. The host keypair is always assumed to be present because having an OpenSSH server usually implies that these are already generated. Still, since during arena initialization (which is performed from main via SSH), the arena keys must match those on main, you may want to provide pre-generated keys during provisioning so that you can be sure that the keys you are installing to the arena and those you are installing to main match.

Use ssh-keygen command on Linux to generate private and public keys as required. You can use rsa or ed25519 keys.

Dyalog APL

To run Dyalog APL you will need a licence and Dyalog Classic and Unicode RPMs for 64-bit arch. TIO has such a licence. If you choose not to get a licence and thus do not have an installation image, the TIO installation script for Dyalog APL will generate errors which can be safely ignored. Dyalog is free for non-commercial usage; you can apply for a licence at

Setup scripts structure

Top level folders:

  • files - those are various files used by setup scripts during setup process.

  • languages - scripts for installing individual languages. Note that not all language are installed with these scripts. Some languages come from dnf, pip, npm or other sources.

  • private - these are files that contain information that may vary from installation to installation. See below.

  • stage - Those are the main setup scripts.

  • misc - miscellaneous scripts not used by the setup scripts. Mainly convenience for maintainers.

  • bootstrap - this is the script that needs to be run to start the setup process

  • run-scripts - a utility script that executes all scripts in a specified directory, such as stage, languages.

Configuring Linode

For both main an arena server you will need to switch to a distribution-supplied kernel, as Linode uses a custom kernel by default. This will enable SELinux the next time your your Fedora 26 image is booted. Once you created a Linode (1024 MiB of RAM, 20 GiB SSD, or better) and deployed the Fedora 26 image you need to boot your linode, and wait until it boots up. Ssh in to make sure it did, or watch the boot progress in Lish.

Go to Linode Manager and edit your linode configuration profile. In the "Boot Settings" section select "GRUB 2" from the "Kernel" drop down, and click "Save changes". On the "Remote Access" tab Click "Add a Private IP". Reboot your linode. Wait for it to back come up. It will take slightly longer than usual, as SeLinux relabeling and another reboot will happen automatically. Now you can follow the rest of the installation steps above.

Setting up main server

Once you cloned the repository into /opt/tiosetup you will need to provide content of private/config file in the private directory. Here is config.default, that you can use as a template:

# Provide commit number or branch for `git checkout` command performed after cloning tryitonline repository
# This allows installing a historic version or a feature branch instead of the master latest

# To be able to use Dyalog APL, you need to download 64-bit Dyalog APL Classic and Unicode
# to /opt This requires a valid Dyalog license. If you have one, you can save your MyDyalog
# username in this file and run the misc/dldyalogapl script manually, before the remaining
# setup scripts. If you do not have a license, you can run the setup script without the
# Dyalog APL archive, but Dyalog APL won't be installed.
# DyalogUser=

# The following five settings are for the domain names used in the setup
# Please read more about them in accompanying documentation.

# Domain where will be hosted

# Domain where will be hosted

# Domain for <language> -><language> redirects.
# This setting is optional and may be left empty or removed entirely.

# This is your email used for LetsEncrypt certificate revocations

# Put your backed up let's encrypt certificates from previous TIO installation in
# private/letsencrypt.tar.gz and leave this setting alone
# Alternatively if you do not have the certs yet and would like to generate them
# change the line to
# UseSavedCerts="n"
# Note that LetsEncrypt limits you to 5 cert requests per week so you do not want
# to keep this setting saying n if your first attempt to install the mirror failed
# see accompanying documentation to find out how to back up generated letsencrypt
# certificates in this case

# You can provide your own SSH key pairs or let them be generated automatically.
# For the root (resp. apache) user, if either an RSA key pair (id_rsa and
# or an ED25519 key pair (id_ed25519 and is found in private/root
# (resp. private/apache), they will be copied in the user's ssh folder. Otherwise, an
# ED25519 key pair will be generated automatically.
# Likewise, if either an RSA key pair (ssh_host_rsa and or an
# ED25519 key pair (ssh_host_ed25519 and is found in private,
# they will replace the pre-generated host keys in /etc/ssh.

# This option should be left turned off ("n"). If it's turned on ("y") certificates
# and selinux configuration will be skipped during setup. This is useful for running
# an offline copy of TryItOnline in a docker image (which does no support selinux)
# Exposing an installation in offline mode to internet is a big security risk and should 
# never be done.

Below is a general scenario of starting main server setup:

cd /opt
dnf install git nano screen openssl wget -y
git clone
cd tiosetup

mkdir private/apache
mkdir private/root

# put your previously saved letsencrypt.tar.gz to private/letsencrypt.tar.gz
# or make edit to edit private/config to read `UseSavedCerts="n"`

# create private/config

# add more scripts to /private to execute at the end of setup process if needed (don't forget to `chmod +x` them if you do)

# put your public key you generated earlier for connection to arena in private/apache/ or private/apache/
# put your private key you generated earlier for connection to arena in private/apache/id_rsa or private/apache/id_ed25519
# put your public key you generated earlier for rsync to arena in private/apache/ or private/root/
# put your private key you generated earlier for rsync to arena in private/apache/id_rsa or private/root/id_ed25519
# put your public key you generated earlier for host authentication in private/
# put your private key you generated earlier for host authentication in private/ssh_host_ed25519_key
# if you have saved certs put them in private/letsencrypt.tar.gz


Logs can be found in /var/log/tioupd directory. You can tail individual items from here for long-running sub-scripts. misc/tiolog script provide a simple bash script for tailing these.

Setup adds as a linked arena, so once setup is finished, you should be able to run Try It Online now.

Setting up arena

You need to provision a fresh linode and configure kernel as described above. You need to add root/apache public keys so that the main server can initialise the arena. The simplest way to do this is just to copy /root/.ssh/authorized_keys over from main. In addition you need to make sure that the host key for ssh (in /etc/ssh/ssh_host_ed25519_key) matches the corresponding public key from main.

Once all the above ready run on main:

tioinit arena_ip arena_name

Where arena_name is an arbitrary name that will be written to /etc/hosts file to correspond to the private ip of the arena linode given as arena_ip. E.g.:

tioinit arena

When syncing has finished (it will take a few minutes), you might want to put newly create arena in rotation:

tiopool add arena
tiopool enable arena

And then remove the main out of rotation

tiopool disable

Dry run

On the main server, you can execute the following to test all languages on the local (main) arena.


To specify an arena to run the tests against do:

tiodryrun -a arena

If setup was successful, you should see the following output after a few minutes.

Testing X languages on arena arena...
Arena arena responded after Y seconds.
Result: X succeeded, 0 failed, 0 not tested

Failed tests will print the language name, the expected output, the actual output, and all pertinent information from STDERR. To see STDERR output (timings, potential warnings, etc.) of successful tests, add the -v or --verbose flag.

It is also possible to run the test for one or more select languages. To do so, specify -l flag. Eg:

tiodryrun -a arena -l python2 python3

Another test utility is available at That one allows running the tests remotely from any client, not just from the main server.


It is possible run similar setup in a docker container, also a pre-build docker container available. This is intended for offline use only, as SeLinux specific commands cannot be run inside a docker container so it has SeLinux disabled. That makes it unsafe to expose on a non trusted networks, such as internet.

See for the details.


Provides setup scripts and instructions for Try It Online




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