backport of commit f880a48fa4

main.go

@@ -416,15 +416,15 @@ func copyOutput(r io.Reader, doneCh chan<- struct{}) {
 	wg.Add(3)
 	go func() {
 		defer wg.Done()
-		io.Copy(os.Stderr, stderrR)
+		_, _ = io.Copy(os.Stderr, stderrR)
 	}()
 	go func() {
 		defer wg.Done()
-		io.Copy(os.Stdout, stdoutR)
+		_, _ = io.Copy(os.Stdout, stdoutR)
 	}()
 	go func() {
 		defer wg.Done()
-		io.Copy(os.Stdout, defaultR)
+		_, _ = io.Copy(os.Stdout, defaultR)
 	}()
 
 	wg.Wait()

packer/plugin-getter/plugins.go

@@ -869,7 +869,7 @@ func (pr *Requirement) InstallLatest(opts InstallOptions) (*Installation, error)
 							}
 							copyFrom, err = f.Open()
 							if err != nil {
-								multierror.Append(errs, fmt.Errorf("failed to open temp file: %w", err))
+								errs = multierror.Append(errs, fmt.Errorf("failed to open temp file: %w", err))
 								return nil, errs
 							}
 							break

packer/plugin_client.go

@@ -198,7 +198,7 @@ func (c *PluginClient) Kill() {
 		return
 	}
 
-	cmd.Process.Kill()
+	_ = cmd.Process.Kill()
 
 	// Wait for the client to finish logging so we have a complete log
 	<-c.doneLogging
@@ -247,7 +247,7 @@ func (c *PluginClient) Start() (net.Addr, error) {
 		r := recover()
 
 		if err != nil || r != nil {
-			cmd.Process.Kill()
+			_ = cmd.Process.Kill()
 		}
 
 		if r != nil {
@@ -264,7 +264,7 @@ func (c *PluginClient) Start() (net.Addr, error) {
 		defer stdout_w.Close()
 
 		// Wait for the command to end.
-		cmd.Wait()
+		_ = cmd.Wait()
 
 		// Log and make sure to flush the logs write away
 		log.Printf("%s: plugin process exited\n", cmd.Path)
@@ -377,7 +377,7 @@ func (c *PluginClient) logStderr(r io.Reader) {
 	for {
 		line, err := bufR.ReadString('\n')
 		if line != "" {
-			c.config.Stderr.Write([]byte(line))
+			_, _ = c.config.Stderr.Write([]byte(line))
 
 			line = strings.TrimRightFunc(line, unicode.IsSpace)
 
@@ -406,7 +406,10 @@ func (c *PluginClient) Client() (*packerrpc.Client, error) {
 
 	if tcpConn, ok := conn.(*net.TCPConn); ok {
 		// Make sure to set keep alive so that the connection doesn't die
-		tcpConn.SetKeepAlive(true)
+		err = tcpConn.SetKeepAlive(true)
+		if err != nil {
+			log.Printf("[ERROR] failed to set keepalive for TCP connection to plugin: %s. Some instability may occur.", err)
+		}
 	}
 
 	client, err := packerrpc.NewClient(conn)

packer/progressbar.go

@@ -62,7 +62,7 @@ func (p *UiProgressBar) TrackProgress(src string, currentSize, totalSize int64,
 			newPb.Finish()
 			p.pbs--
 			if p.pbs <= 0 {
-				p.pool.Stop()
+				_ = p.pool.Stop()
 				p.pool = nil
 			}
 			return nil

post-processor/checksum/post-processor.go

@@ -151,7 +151,7 @@ func (p *PostProcessor) PostProcess(ctx context.Context, ui packersdk.Ui, artifa
 				return nil, false, true, fmt.Errorf("unable to compute %s hash for %s", ct, art)
 			}
 			fr.Close()
-			fw.WriteString(fmt.Sprintf("%x\t%s\n", h.Sum(nil), filepath.Base(art)))
+			_, _ = fw.WriteString(fmt.Sprintf("%x\t%s\n", h.Sum(nil), filepath.Base(art)))
 			fw.Close()
 			h.Reset()
 		}

post-processor/compress/post-processor.go

@@ -371,7 +371,7 @@ func makePgzipWriter(output io.WriteCloser, compressionLevel int) (io.WriteClose
 	if err != nil {
 		return nil, ErrInvalidCompressionLevel
 	}
-	gzipWriter.SetConcurrency(500000, runtime.GOMAXPROCS(-1))
+	_ = gzipWriter.SetConcurrency(500000, runtime.GOMAXPROCS(-1))
 	return gzipWriter, nil
 }
 

provisioner/shell/provisioner.go

@@ -203,7 +203,7 @@ func (p *Provisioner) Provision(ctx context.Context, ui packersdk.Ui, comm packe
 
 		// Write our contents to it
 		writer := bufio.NewWriter(tf)
-		writer.WriteString(fmt.Sprintf("#!%s\n", p.config.InlineShebang))
+		_, _ = writer.WriteString(fmt.Sprintf("#!%s\n", p.config.InlineShebang))
 		for _, command := range p.config.Inline {
 			p.config.ctx.Data = generatedData
 			command, err := interpolate.Render(command, &p.config.ctx)

provisioner/windows-restart/provisioner.go

@@ -165,7 +165,10 @@ var waitForRestart = func(ctx context.Context, p *Provisioner, comm packersdk.Co
 		if cmd.ExitStatus() == 0 {
 			// Cancel reboot we created to test if machine was already rebooting
 			cmd = &packersdk.RemoteCmd{Command: abortcommand}
-			cmd.RunWithUi(ctx, comm, ui)
+			err = cmd.RunWithUi(ctx, comm, ui)
+			if err != nil {
+				log.Printf("[ERROR] failed to run remote shutdown command: %s, build will likely hang.", err)
+			}
 			break
 		}
 	}
@@ -249,7 +252,11 @@ var waitForCommunicator = func(ctx context.Context, p *Provisioner) error {
 		cmdModuleLoad.Stdout = &buf
 		cmdModuleLoad.Stdout = io.MultiWriter(cmdModuleLoad.Stdout, &buf2)
 
-		cmdModuleLoad.RunWithUi(ctx, p.comm, p.ui)
+		err := cmdModuleLoad.RunWithUi(ctx, p.comm, p.ui)
+		if err != nil {
+			log.Printf("[ERROR] failed to run restart command on guest: %s. Build may hang.", err)
+		}
+
 		stdoutToRead := buf2.String()
 
 		if !strings.Contains(stdoutToRead, "restarted.") {