Developing Software

This page is all about programming your own software (C, Fortran, Java, Julia, Octave, R, etc.) from CoCalc. A highly related page is the FAQ for Utilizing External Tools from CoCalc. There is also a separate page about Jupyter Notebooks and Sage Worksheets.


If you don’t find what you need, or if you’d like to ask a question, then please email at any time. We’d love to hear from you! Please include a link to any relevant project or document (copy and paste the URL address in your browser) as part of your email.


Will my code keep running if I disconnect?

Even if my computer is put to sleep? Or do I need to have a machine open in order for the process to run?

You definitely do not need to have your computer awake, or a window open, for your project to keep working. However, this is controlled by something called an “idle timeout,” described in the next question.

What is an “idle timeout?”

Under Project Settings (that’s the wrench icon) there is an entry under Project usage and quotas (left-hand side), which will tell you how long the process will run “in the background.” There is an idle timeout for each project, and it will be completely stopped (the technical term in UNIX is “killed”) if you don’t actively edit a file for that amount of time.

The default for free projects is 30 minutes. You can increase this to 24 hours for only $14 per month. This means that if you use your project a little bit once per day, then it will never timeout.

However, free projects have another limitation. A free project can be “killed” (stopped) at any time, whatsoever. This will happen at least once per day. You have to keep this in mind when designing your project. (For example, use checkpointing.) In contrast, all paid projects are immune to this issue. See also Project Upgrades.

Timeout/Killed calculations

If I have code that has been running for a while, and it times out or is otherwise “killed” (see previous question), what happens to the output?

If you are using a classical Jupyter notebook, then all output that is printed will be lost if no browser is viewing it. This is a major design flaw in Jupyter. CoCalc’s Jupyter implemenetation behaves much better!

In contrast, Sage Worksheets will capture output even if no browser is observing them.

You can also (of course) write to a file on disk, which might be preferable in some cases.

Limitations of long-running computations

Open your project and click on Settings. The default limitations are listed under “Quotas” in the lower left. These can be raised, as mentioned there. Notes:

  • Projects without “member hosting” upgrade can get restarted regularly (these are hosted on Google preemptible instances). You can check if a VM rebooted by typing “uptime”.
  • If a project isn’t used (via the web-based UI) for the idle timeout (as listed in quotas), then all processes in that project are terminated and the user is removed (so ssh into the project also is not possible). You can pay to raise the idle timeout. See also What is an “idle timeout?”.

Is .bashrc or .bash_profile called on startup?

~/.bashrc is run on startup and ~/.bash_profile is not! Hence, use ~/.bashrc to customize your setup, and you can also use ~/.bash_aliases for your aliases (see ~/.bashrc).

Sage Worksheets

Adjust the output cut-offs

It is an extremely common programming mistake to write an infinite loop, particularly when first learning about loops. Because CoCalc assumes an experienced programmer, the “cutoff limits” are set rather high. Users new to programming might want to set that limit lower, so that their screen isn’t overflowing with repeated lines in the event that they inadvertently code up an infinite loop. (By the way, this works in all languages, not just Sage, e.g. R, C, FORTRAN, whatever you’d like.)

You can type:

print sage_server.MAX_STDOUT_SIZE

at any time to find out the current limit. By default, it is 40,000.

Then, you can change it by typing something like this:

sage_server.MAX_STDOUT_SIZE = 500

Note, this is 500 characters. Take care to ensure that the setting of this variable will be executed before your code starts. If you type

sage_server.MAX_STDOUT_SIZE = 500

for i in range(0,1000):
    print i

then it will be cut off somewhere in the middle of printing 152, because you need to count each digit, as well as the invisible “end of line” symbol. At the 501st character, the computation is stopped, and there is no more output.

By the way, it isn’t just the case that the output is truncated at this point. The computation is halted as well. (The technical term for this is that “the process is killed.”)

Raise the limit on the number of output messages per cell

import sage_server

See this published worksheet for more details.

Also, type sage_server.[tab key] to see information about other limitations.

Custom Modules

Put an executable file with this content in $HOME/bin/sage:

First, check where the global Sage install is by running which sage. Most likely, it is at /ext/bin/sage. Then create the file with the content:

#!/usr/bin/env bash
SAGE_PATH=$HOME/NEW_MODULE /ext/bin/sage "[email protected]"

You could do this by making a new directory called bin, then a new file in there called “sage”. In the terminal type the following to make “sage” executable:

cd; cd bin; chmod +x sage

Then restart the worksheet server by going project settings and clicking “Restart → Worksheet server”.

Now any newly (re-)started worksheet will run with the above modified SAGE_PATH. Since SAGE_PATH is added to PYTHONPATH when Sage starts, this does what you want.

(From Nathan Dunfield) Another approach, which also works now and doesn’t require the custom $HOME/bin/sage, is to use <>.

That is, one installs a module with sage -python install --user and it’s dumped into


This location is searched automatically by Sage’s Python without any intervention on the part of the user. (However, you might have to restart the worksheet server to access newly installed modules from a worksheet.) One can also put modules into the user’s site-packages by hand and Sage will find them.

Julia in a Sage Worksheet

  1. Click +New, type a filename, then click the “Sage Worksheet” button.
  2. To evaluate code using Julia, begin the cell with %julia, type the code, then press shift+enter.
  3. Type %default_mode julia in a cell and press shift+enter; now all cells will be evaluated using Julia by default. If you need to switch back, use %default_mode sage (or %sage to just switch back for one cell).

Detect Sage Worksheet Environment

If your code is running in a CoCalc worksheet, then the global variable __SAGEWS__ will be defined.

Functions specific to Sage worksheets

Type salvus.[tab key] to see the auto-complete list of functions or run dir(salvus).

Run Sage locally, on my own machine

There is a lovely tutorial on the web to help you do exactly that: Sage Installation Guide.

Custom Sage binaries

See the instructions, immediately below, on using a custom built-from-scratch copy of Sage. Just substitute your own .tar.gz file for the official build of Sage.

Custom built-from-source Sage


This requires a upgraded project and takes hours! By default CoCalc projects have an idle timeout that is smaller. (see What is an “idle timeout?”) If you aren’t editing files in the project, your build will get killed part of the way through. If you’re doing legit Sage development, email THE LINK TO YOUR PROJECT to and we will increase the idle timeout, disk space, RAM, etc, so you can contribute to Sage.

Open a Linux Terminal. Grab the source tarball (requires network access). You can browse to find recent releases and testing versions.

To build, do the following in your terminal (no need to worry about screen or tmux, of course, since sessions are persistent even if your browser leaves), and check back in a few hours:

tar xvf sage-6.10.tar.gz && cd sage-6.10 && make

After doing that, do something like this in the terminal:

cd; mkdir -p bin; cd bin; ln -s ~/sage-6.10/sage .

Then restart your worksheet server (in project settings). Then for that project, you’ll have your own 100% customizable copy of Sage; and moreover, when the system-wide Sage is upgraded, your project isn’t impacted at all – that sort of stability is a major win for some people. This also uses little extra disk space in backups/snapshots, because of de-duplication. You can of course also install any custom packages you want into this copy of Sage. You can also help improve Sage: Developer Guide.

If you want to do Sage development see How to develop for Sage using SageMath.

Important: Whenever you change Python code installed in that copy of Sage, you may have to restart the worksheet server and any running worksheets. This is inconvenient, but is necessary because the worksheet server starts one copy of Sage, then forks off additional copies each time you open a new worksheet, which greatly reduces the time from when you open a worksheet until it actually starts computing things.

Also Important: If your copy of Sage is messed up in some way, then the worksheet server can’t start, hence worksheets won’t open. To debug this, open a terminal and do this:

~$ cd .smc
~/.smc$ sage
you should see an error here, e.g.,

and fix whatever error you see. Also look at log files in ~/.smc/sage_server/


Custom Python3

With full network access enabled, you can download and compile Python 3 this way. Last line sets a symlink to make it your default!

apt-get source python3.4-dev
cd python3.4-3.4.0/
./configure --prefix=$HOME
make install
cd ..
pip3 install numpy
pip3 install scipy
pip3 install matplotlib
pip3 install ipython
pip3 install pyzmq
pip3 install jinja2
pip3 install tornado
ln -s ~/bin/python3 ~/bin/python

Run plotly in a Jupyter notebook

You need to run Plotly plots in CoCalc under the Plain Jupyter Server. For more information, see the Jupyter Classic / Modern page.

Another option is to use the Plotly Dash framework: here is a working example running Dash from a CoCalc terminal

R Statistical Software

I would like to install new R packages

Open a terminal windows and type


Then you can install packages as usual


The above will install R packages for use with CoCalc worksheets (%r mode) and Jupyter notebooks using default R. The Sage binary may be built with a different release of R. Use R-sage instead of R to install packages for it.

Note that you must also upgrade your project to have internet access (requires a subscription) and hence allow R to download the packages from the package server.

Otherwise you have to download the tarball of the R package to your own machine, and Upload Files it to your project. Then, you can tell R to install the package directly from there as a local file.

Use R in a Sage worksheet

  1. Click +New, type a filename, then click the “Sage Worksheet” button.
  2. To evaluate code using R, begin the cell with %r, type the code, then press shift+enter.
  3. Type %default_mode r in a cell and press shift+enter; now all cells will be evaluated using R by default. If you need to switch back, use %default_mode sage.

Override the default width and height for R SVG figures in a CoCalc worksheet

To set width to 10 inches and height to 4 inches, use the sage command:

r.set_plot_options(width=10, height=4)

If you have set default_mode to r, then enter the command in a sage mode cell:

%sage r.set_plot_options(width=10, height=4)

You can change it by typing it again.


I’ve put an example Octave Jupyter notebook and an Octave CoCalc worksheet here:

Besides Jupyter and CoCalc worksheets, you can also work in a Linux Terminal: Click “+New”, click Terminal, and type “octave” on the command line, and this should work well. You can type “+New”, enter a filename that ends with .m, and edit it, then load it into the command line (by typing the filename without the extension).

Other Languages

Create, compile and run a C program

  1. Click +New, type a filename ending in “.c”, e.g., foo.c, and click “Create File” (or just press return).

  2. Paste this code into the file:

    int main(void) {
        printf("Hello World\n");
        printf("this is CoCalc!\n");
  3. Open a Linux Terminal by clicking +New, clicking “Command Line Terminal” (or typing a filename ending in .term), and type gcc foo.c -o foo. Finally, run the program by typing `./foo.

Create, compile and run a Java program

  1. Create a file containing
public class HelloWorld {
    public static void main (String[] args) {
        System.out.println ("Hello World!");
  1. Create a terminal and run javac to compile your program.
  2. Run java HelloWorld to see the output.