Best practice

Manage sessions with Linux’s screen command

Running short test Grain sessions on your terminal can be a good start, but if you want to keep the session running for a bit longer and check back later, screen is your friend. With screen, you can create and manage virtual terminals, which persist even after you log out from your main terminal. You can even create multiple virtual terminals and switch among them: useful for running multiple Grain sessions concurrently. To start a new session, do

screen -S mysession

You are now in a new screen session, and you can run commands as you usually do. (e.g. start a head process within) To detach from the current session, press Ctrl-a then followed by d. To reattach the session at any time

screen -r mysession

In a screen session, when you are done, simply Ctrl-d to log out as usual.

You can create multiple screen sessions; just run screen -S with different names. To list all running screen sessions, do

screen -list

Because all screen sessions live on the same host, sharing the scheduler among multiple Grain sessions becomes easy. Recall that Grain head processes running on the same host with the same head.listen address will attach to the same scheduler.

Quickly switch between different Grain configs

If environment variable GRAIN_CONFIG is set, Grain will look for the config file specified by it. We can take advantage of this setting and specify different configs for different environments. For example, if you have a project to be run on two different supercomputing clusters, A and B, you can put config files grain.a.toml and grain.b.toml in the project directory. Then, you can set environment variable GRAIN_CONFIG to grain.a.toml on cluster A’s login profile, and grain.b.toml on cluster B’s login profile. In this way, Grain will look for the right config file regardless of the cluster you are currently logged into.