Write ~/.lima/<INSTANCE>/ssh.config

```console
$ limactl ls --format='{{.SSHConfigFile}}' default
/Users/example/.lima/default/ssh.config
```

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

README.md

@@ -225,6 +225,20 @@ Use `<INSTANCE>:<FILENAME>` to specify a source or target inside an instance.
 
 `limactl disk list`: list all existing disks
 
+#### `limactl show-ssh`
+- `limactl show-ssh --format=cmd <INSTANCE>` (default): Full `ssh` command line
+- `limactl show-ssh --format=args <INSTANCE>`: Similar to the `cmd` format but omits `ssh` and the destination address
+- `limactl show-ssh --format=options <INSTANCE>`: ssh option key value pairs
+- `limactl show-ssh --format=config <INSTANCE>`: `~/.ssh/config` format
+
+The config file is also automatically created inside the instance directory:
+```console
+$ limactl ls --format='{{.SSHConfigFile}}' default
+/Users/example/.lima/default/ssh.config
+
+$ ssh -F /Users/example/.lima/default/ssh.config lima-default
+```
+
 #### `limactl completion`
 - To enable bash completion, add `source <(limactl completion bash)` to `~/.bash_profile`.
 

cmd/limactl/show_ssh.go

@@ -34,6 +34,10 @@ const showSSHExample = `
       User example
       Hostname 127.0.0.1
       Port 60022
+
+  To show the config file path:
+    $ limactl ls --format='{{.SSHConfigFile}}' default
+    /Users/example/.lima/default/ssh.config
 `
 
 func newShowSSHCommand() *cobra.Command {

docs/internal.md

@@ -54,6 +54,7 @@ VZ:
 
 SSH:
 - `ssh.sock`: SSH control master socket
+- `ssh.config`: SSH config file, printed by `limactl show-ssh --format=config-file` . Not consumed by Lima itself.
 
 Guest agent:
 - `ga.sock`: Forwarded to `/run/lima-guestagent.sock` in the guest, via SSH

pkg/hostagent/hostagent.go

@@ -1,6 +1,7 @@
 package hostagent
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -111,6 +112,9 @@ func New(instName string, stdout io.Writer, sigintCh chan os.Signal, opts ...Opt
 	if err != nil {
 		return nil, err
 	}
+	if err = writeSSHConfigFile(inst, sshLocalPort, sshOpts); err != nil {
+		return nil, err
+	}
 	sshConfig := &ssh.SSHConfig{
 		AdditionalArgs: sshutil.SSHArgsFromOpts(sshOpts),
 	}
@@ -150,6 +154,28 @@ func New(instName string, stdout io.Writer, sigintCh chan os.Signal, opts ...Opt
 	return a, nil
 }
 
+func writeSSHConfigFile(inst *store.Instance, sshLocalPort int, sshOpts []string) error {
+	if inst.Dir == "" {
+		return fmt.Errorf("directory is unknown for the instance %q", inst.Name)
+	}
+	var b bytes.Buffer
+	if _, err := fmt.Fprintf(&b, `# This SSH config file can be passed to 'ssh -F'.
+# This file is created by Lima, but not used by Lima itself currently.
+# Modifications to this file will be lost on restarting the Lima instance.
+`); err != nil {
+		return err
+	}
+	if err := sshutil.Format(&b, inst.Name, sshutil.FormatConfig,
+		append(sshOpts,
+			"Hostname=127.0.0.1",
+			fmt.Sprintf("Port=%d", sshLocalPort),
+		)); err != nil {
+		return err
+	}
+	fileName := filepath.Join(inst.Dir, filenames.SSHConfig)
+	return os.WriteFile(fileName, b.Bytes(), 0600)
+}
+
 func determineSSHLocalPort(y *limayaml.LimaYAML, instName string) (int, error) {
 	if *y.SSH.LocalPort > 0 {
 		return *y.SSH.LocalPort, nil

pkg/store/filenames/filenames.go

@@ -37,6 +37,7 @@ const (
 	SerialLog          = "serial.log"
 	SerialSock         = "serial.sock"
 	SSHSock            = "ssh.sock"
+	SSHConfig          = "ssh.config"
 	GuestAgentSock     = "ga.sock"
 	HostAgentPID       = "ha.pid"
 	HostAgentSock      = "ha.sock"

pkg/store/instance.go

@@ -47,6 +47,7 @@ type Instance struct {
 	AdditionalDisks []limayaml.Disk    `json:"additionalDisks,omitempty"`
 	Networks        []limayaml.Network `json:"network,omitempty"`
 	SSHLocalPort    int                `json:"sshLocalPort,omitempty"`
+	SSHConfigFile   string             `json:"sshConfigFile,omitempty"`
 	HostAgentPID    int                `json:"hostAgentPID,omitempty"`
 	DriverPID       int                `json:"driverPID,omitempty"`
 	Errors          []error            `json:"errors,omitempty"`
@@ -101,6 +102,7 @@ func Inspect(instName string) (*Instance, error) {
 	inst.AdditionalDisks = y.AdditionalDisks
 	inst.Networks = y.Networks
 	inst.SSHLocalPort = *y.SSH.LocalPort // maybe 0
+	inst.SSHConfigFile = filepath.Join(instDir, filenames.SSHConfig)
 
 	inst.HostAgentPID, err = ReadPIDFile(filepath.Join(instDir, filenames.HostAgentPID))
 	if err != nil {