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// Copyright 2016 Canonical Ltd.
// Copyright 2016 Cloudbase Solutions
// Licensed under the LGPLv3, see LICENCE file for details.
package exec
import (
var logger = loggo.GetLogger("juju.util.exec")
// Parameters for RunCommands. Commands contains one or more commands to be
// executed using bash or PowerShell. If WorkingDir is set, this is passed
// through. Similarly if the Environment is specified, this is used
// for executing the command.
// TODO: refactor this to use a config struct and a constructor. Remove todo
// and extra code from WaitWithCancel once this is done.
type RunParams struct {
Commands string
WorkingDir string
Environment []string
Clock clock.Clock
KillProcess func(*os.Process) error
User string
tempDir string
stdout *bytes.Buffer
stderr *bytes.Buffer
ps *exec.Cmd
// ExecResponse contains the return code and output generated by executing a
// command.
type ExecResponse struct {
Code int
Stdout []byte
Stderr []byte
// mergeEnvironment takes in a string array representing the desired environment
// and merges it with the current environment. On Windows, clearing the environment,
// or having missing environment variables, may lead to standard go packages not working
// (os.TempDir relies on $env:TEMP), and powershell erroring out
// Currently this function is only used for windows
func mergeEnvironment(env []string) []string {
if env == nil {
return nil
m := make(map[string]string)
var tmpEnv []string
for _, val := range os.Environ() {
varSplit := strings.SplitN(val, "=", 2)
m[varSplit[0]] = varSplit[1]
for _, val := range env {
varSplit := strings.SplitN(val, "=", 2)
m[varSplit[0]] = varSplit[1]
for key, val := range m {
tmpEnv = append(tmpEnv, key+"="+val)
return tmpEnv
// shellAndArgs returns the name of the shell command and arguments to run the
// specified script. shellAndArgs may write into the provided temporary
// directory, which will be maintained until the process exits.
func shellAndArgs(tempDir, script, user string) (string, []string, error) {
var scriptFile string
var cmd string
var args []string
switch runtime.GOOS {
case "windows":
scriptFile = filepath.Join(tempDir, "script.ps1")
cmd = "powershell.exe"
args = []string{
"-ExecutionPolicy", "RemoteSigned",
"-File", scriptFile,
// Exceptions don't result in a non-zero exit code by default
// when using -File. The exit code of an explicit "exit" when
// using -Command is ignored and results in an exit code of 1.
// We use -File and trap exceptions to cover both.
script = "trap {Write-Error $_; exit 1}\n" + script
scriptFile = filepath.Join(tempDir, "")
if user == "" {
cmd = "/bin/bash"
args = []string{scriptFile}
} else {
// Need to make the tempDir readable by all so the user can see it.
err := os.Chmod(tempDir, 0755)
if err != nil {
return "", nil, errors.Annotatef(err, "making tempdir readable by %q", user)
cmd = "/bin/su"
args = []string{user, "--login", "--command", fmt.Sprintf("/bin/bash %s", scriptFile)}
err := ioutil.WriteFile(scriptFile, []byte(script), 0644)
if err != nil {
return "", nil, err
return cmd, args, nil
// Run sets up the command environment (environment variables, working dir)
// and starts the process. The commands are passed into bash on Linux machines
// and to powershell on Windows machines.
func (r *RunParams) Run() error {
if runtime.GOOS == "windows" {
r.Environment = mergeEnvironment(r.Environment)
tempDir, err := ioutil.TempDir("", "juju-exec")
if err != nil {
return err
shell, args, err := shellAndArgs(tempDir, r.Commands, r.User)
if err != nil {
if err := os.RemoveAll(tempDir); err != nil {
logger.Warningf("failed to remove temporary directory: %v", err)
return err
} = exec.Command(shell, args...)
if r.Environment != nil { = r.Environment
if r.WorkingDir != "" { = r.WorkingDir
// If there is no user provided KillProcess function we
// use the default one.
if r.KillProcess == nil {
r.KillProcess = KillProcess
r.tempDir = tempDir
r.stdout = &bytes.Buffer{}
r.stderr = &bytes.Buffer{} = r.stdout = r.stderr
// Process returns the *os.Process instance of the current running process
// This will allow us to kill the process if needed, or get more information
// on the process
func (r *RunParams) Process() *os.Process {
if != nil && != nil {
return nil
// Wait blocks until the process exits, and returns an ExecResponse type
// containing stdout, stderr and the return code of the process. If a non-zero
// return code is returned, this is collected as the code for the response and
// this does not classify as an error.
func (r *RunParams) Wait() (*ExecResponse, error) {
var err error
if == nil {
return nil, errors.New("No process has been started yet")
err =
if err := os.RemoveAll(r.tempDir); err != nil {
logger.Warningf("failed to remove temporary directory: %v", err)
result := &ExecResponse{
Stdout: r.stdout.Bytes(),
Stderr: r.stderr.Bytes(),
if ee, ok := err.(*exec.ExitError); ok && err != nil {
status := ee.ProcessState.Sys().(syscall.WaitStatus)
if status.Exited() {
// A non-zero return code isn't considered an error here.
result.Code = status.ExitStatus()
err = nil
logger.Infof("run result: %v", ee)
return result, err
// ErrCancelled is returned by WaitWithCancel in case it successfully manages to kill
// the running process.
var ErrCancelled = errors.New("command cancelled")
// timeWaitForKill reperesent the time we wait after attempting to kill a
// process before bailing out and returning.
const timeWaitForKill = 30 * time.Second
type resultWithError struct {
execResult *ExecResponse
err error
// WaitWithCancel waits until the process exits or until a signal is sent on the
// cancel channel. In case a signal is sent it first tries to kill the process and
// return ErrCancelled. If it fails at killing the process it will return anyway
// and report the problematic PID.
func (r *RunParams) WaitWithCancel(cancel <-chan struct{}) (*ExecResponse, error) {
// TODO: Remove this once we make Clock a required field
_clock := r.Clock
if _clock == nil {
_clock = clock.WallClock
done := make(chan resultWithError, 1)
go func() {
defer close(done)
waitResult, err := r.Wait()
done <- resultWithError{waitResult, err}
select {
case resWithError := <-done:
return resWithError.execResult, errors.Trace(resWithError.err)
case <-cancel:
logger.Debugf("attempting to kill process")
err := r.KillProcess(
if err != nil {
logger.Debugf("kill returned: %s", err)
// After we issue a kill we expect the wait above to return within timeWaitForKill.
// In case it doesn't we just go on and assume the process is stuck, but we don't block
select {
case resWithError := <-done:
return resWithError.execResult, ErrCancelled
case <-_clock.After(timeWaitForKill):
return nil, errors.Errorf("tried to kill process %v, but timed out",
// RunCommands executes the Commands specified in the RunParams using
// powershell on windows, and '/bin/bash -s' on everything else,
// passing the commands through as stdin, and collecting
// stdout and stderr. If a non-zero return code is returned, this is
// collected as the code for the response and this does not classify as an
// error.
func RunCommands(run RunParams) (*ExecResponse, error) {
err := run.Run()
if err != nil {
return nil, err
return run.Wait()
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