I’m going to start a series that I read runc “cover-to-cover”.
runc is a small command which reads the OCI Runtime Specification and runs Linux containers. Docker, containerd or even CRI-O use runc under the hood by default.
But first, let’s talk about libcontainer
The part of runc is called libcontainer due to the origin. I’d like to cover the fact first since it is fascinating.
In 2014, Docker was attempting to extract its core as libcontainer.
Second, we are introducing a new built-in execution driver which is shipping alongside the LXC driver. This driver is based on libcontainer, a pure Go library which we developed to access the kernel’s container APIs directly, without any other dependencies.
While it didn’t thrive as a standalone project, libcontainer eventually became runc in 2015.
Docker has taken the entire contents of the libcontainer project, including [nsinit], and all modifications needed to make it run independently of Docker, and donated it to this effort. This codebase, called runC, can be found at github/opencontainers/runc. libcontainer will cease to operate as a separate project.
Because of that, a lot of low-level “guts” of runc is in libcontainer/ directory.
Where is the main function?
runc’s main function is in main.go. runc uses urfave/cli for handling its sub-commands and parsing the command line parameters.
func main() {
app := cli.NewApp()
app.Name = "runc"
app.Usage = usage
...
app.Commands = []cli.Command{
checkpointCommand,
createCommand,
deleteCommand,
eventsCommand,
execCommand,
initCommand,
killCommand,
listCommand,
pauseCommand,
psCommand,
restoreCommand,
resumeCommand,
runCommand,
specCommand,
startCommand,
stateCommand,
updateCommand,
}
...All of the command functions are in separate Go files in the main package, such as checkpoint.go.
That’s it for today!
I’m going to read create.go this week.