Add .containerenv file

docs/podman-run.1.md

@@ -21,6 +21,14 @@ If the IMAGE is not already loaded then **podman run** will pull the IMAGE, and
 all image dependencies, from the repository in the same way running **podman
 pull** IMAGE, before it starts the container from that image.
 
+Several files will be automatically created within the container. These include
+`/etc/hosts`, `/etc/hostname`, and `/etc/resolv.conf` to manage networking.
+These will be based on the host's version of the files, though they can be
+customized with options (for example, **--dns** will override the host's DNS
+servers in the created `resolv.conf`). Additionally, an empty file is created in
+each container to indicate to programs they are running in a container. This file
+is located at `/run/.containerenv`.
+
 ## OPTIONS
 **--add-host**=[]
    Add a custom host-to-IP mapping (host:ip)

libpod/container_internal.go

@@ -672,6 +672,17 @@ func (c *Container) makeBindMounts() error {
 		c.state.BindMounts["/etc/hostname"] = hostnamePath
 	}
 
+	// Make .containerenv
+	// Empty file, so no need to recreate if it exists
+	if _, ok := c.state.BindMounts["/run/.containerenv"]; !ok {
+		// Empty string for now, but we may consider populating this later
+		containerenvPath, err := c.writeStringToRundir(".containerenv", "")
+		if err != nil {
+			return errors.Wrapf(err, "error creating containerenv file for container %s", c.ID())
+		}
+		c.state.BindMounts["/run/.containerenv"] = containerenvPath
+	}
+
 	return nil
 }
 
@@ -898,6 +909,7 @@ func (c *Container) generateSpec() (*spec.Spec, error) {
 
 	g.SetHostname(c.Hostname())
 	g.AddProcessEnv("HOSTNAME", g.Spec().Hostname)
+	g.AddProcessEnv("container", "libpod")
 
 	return g.Spec(), nil
 }