diff --git a/main-mshell.go b/main-mshell.go
index d7f0a0adb..4e58eba23 100644
--- a/main-mshell.go
+++ b/main-mshell.go
@@ -13,132 +13,131 @@ import (
 	"strings"
 
 	"github.com/scripthaus-dev/mshell/pkg/base"
-	"github.com/scripthaus-dev/mshell/pkg/cmdtail"
 	"github.com/scripthaus-dev/mshell/pkg/packet"
 	"github.com/scripthaus-dev/mshell/pkg/server"
 	"github.com/scripthaus-dev/mshell/pkg/shexec"
 	"golang.org/x/sys/unix"
 )
 
-func doMainRun(pk *packet.RunPacketType, sender *packet.PacketSender) {
-	err := shexec.ValidateRunPacket(pk)
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("invalid run packet: %v", err))
-		return
-	}
-	fileNames, err := base.GetCommandFileNames(pk.CK)
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot get command file names: %v", err))
-		return
-	}
-	cmd, err := shexec.MakeRunnerExec(pk.CK)
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot make mshell command: %v", err))
-		return
-	}
-	cmdStdin, err := cmd.StdinPipe()
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot pipe stdin to command: %v", err))
-		return
-	}
-	// touch ptyout file (should exist for tailer to work correctly)
-	ptyOutFd, err := os.OpenFile(fileNames.PtyOutFile, os.O_CREATE|os.O_TRUNC|os.O_APPEND|os.O_WRONLY, 0600)
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot open pty out file '%s': %v", fileNames.PtyOutFile, err))
-		return
-	}
-	ptyOutFd.Close() // just opened to create the file, can close right after
-	runnerOutFd, err := os.OpenFile(fileNames.RunnerOutFile, os.O_CREATE|os.O_TRUNC|os.O_APPEND|os.O_WRONLY, 0600)
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot open runner out file '%s': %v", fileNames.RunnerOutFile, err))
-		return
-	}
-	defer runnerOutFd.Close()
-	cmd.Stdout = runnerOutFd
-	cmd.Stderr = runnerOutFd
-	err = cmd.Start()
-	if err != nil {
-		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("error starting command: %v", err))
-		return
-	}
-	go func() {
-		err = packet.SendPacket(cmdStdin, pk)
-		if err != nil {
-			sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("error sending forked runner command: %v", err))
-			return
-		}
-		cmdStdin.Close()
+// func doMainRun(pk *packet.RunPacketType, sender *packet.PacketSender) {
+// 	err := shexec.ValidateRunPacket(pk)
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("invalid run packet: %v", err))
+// 		return
+// 	}
+// 	fileNames, err := base.GetCommandFileNames(pk.CK)
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot get command file names: %v", err))
+// 		return
+// 	}
+// 	cmd, err := shexec.MakeRunnerExec(pk.CK)
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot make mshell command: %v", err))
+// 		return
+// 	}
+// 	cmdStdin, err := cmd.StdinPipe()
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot pipe stdin to command: %v", err))
+// 		return
+// 	}
+// 	// touch ptyout file (should exist for tailer to work correctly)
+// 	ptyOutFd, err := os.OpenFile(fileNames.PtyOutFile, os.O_CREATE|os.O_TRUNC|os.O_APPEND|os.O_WRONLY, 0600)
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot open pty out file '%s': %v", fileNames.PtyOutFile, err))
+// 		return
+// 	}
+// 	ptyOutFd.Close() // just opened to create the file, can close right after
+// 	runnerOutFd, err := os.OpenFile(fileNames.RunnerOutFile, os.O_CREATE|os.O_TRUNC|os.O_APPEND|os.O_WRONLY, 0600)
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot open runner out file '%s': %v", fileNames.RunnerOutFile, err))
+// 		return
+// 	}
+// 	defer runnerOutFd.Close()
+// 	cmd.Stdout = runnerOutFd
+// 	cmd.Stderr = runnerOutFd
+// 	err = cmd.Start()
+// 	if err != nil {
+// 		sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("error starting command: %v", err))
+// 		return
+// 	}
+// 	go func() {
+// 		err = packet.SendPacket(cmdStdin, pk)
+// 		if err != nil {
+// 			sender.SendCKErrorPacket(pk.CK, fmt.Sprintf("error sending forked runner command: %v", err))
+// 			return
+// 		}
+// 		cmdStdin.Close()
 
-		// clean up zombies
-		cmd.Wait()
-	}()
-}
+// 		// clean up zombies
+// 		cmd.Wait()
+// 	}()
+// }
 
-func doGetCmd(tailer *cmdtail.Tailer, pk *packet.GetCmdPacketType, sender *packet.PacketSender) error {
-	err := tailer.AddWatch(pk)
-	if err != nil {
-		return err
-	}
-	return nil
-}
+// func doGetCmd(tailer *cmdtail.Tailer, pk *packet.GetCmdPacketType, sender *packet.PacketSender) error {
+// 	err := tailer.AddWatch(pk)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return nil
+// }
 
-func doMain() {
-	homeDir := base.GetHomeDir()
-	err := os.Chdir(homeDir)
-	if err != nil {
-		packet.SendErrorPacket(os.Stdout, fmt.Sprintf("cannot change directory to $HOME '%s': %v", homeDir, err))
-		return
-	}
-	_, err = base.GetMShellPath()
-	if err != nil {
-		packet.SendErrorPacket(os.Stdout, err.Error())
-		return
-	}
-	packetParser := packet.MakePacketParser(os.Stdin)
-	sender := packet.MakePacketSender(os.Stdout)
-	tailer, err := cmdtail.MakeTailer(sender)
-	if err != nil {
-		packet.SendErrorPacket(os.Stdout, err.Error())
-		return
-	}
-	go tailer.Run()
-	initPacket := shexec.MakeInitPacket()
-	sender.SendPacket(initPacket)
-	for pk := range packetParser.MainCh {
-		if pk.GetType() == packet.RunPacketStr {
-			doMainRun(pk.(*packet.RunPacketType), sender)
-			continue
-		}
-		if pk.GetType() == packet.GetCmdPacketStr {
-			err = doGetCmd(tailer, pk.(*packet.GetCmdPacketType), sender)
-			if err != nil {
-				errPk := packet.MakeErrorPacket(err.Error())
-				sender.SendPacket(errPk)
-				continue
-			}
-			continue
-		}
-		if pk.GetType() == packet.CdPacketStr {
-			cdPacket := pk.(*packet.CdPacketType)
-			err := os.Chdir(cdPacket.Dir)
-			resp := packet.MakeResponsePacket(cdPacket.ReqId)
-			if err != nil {
-				resp.Error = err.Error()
-			} else {
-				resp.Success = true
-			}
-			sender.SendPacket(resp)
-			continue
-		}
-		if pk.GetType() == packet.ErrorPacketStr {
-			errPk := pk.(*packet.ErrorPacketType)
-			errPk.Error = "invalid packet sent to mshell: " + errPk.Error
-			sender.SendPacket(errPk)
-			continue
-		}
-		sender.SendErrorPacket(fmt.Sprintf("invalid packet '%s' sent to mshell", pk.GetType()))
-	}
-}
+// func doMain() {
+// 	homeDir := base.GetHomeDir()
+// 	err := os.Chdir(homeDir)
+// 	if err != nil {
+// 		packet.SendErrorPacket(os.Stdout, fmt.Sprintf("cannot change directory to $HOME '%s': %v", homeDir, err))
+// 		return
+// 	}
+// 	_, err = base.GetMShellPath()
+// 	if err != nil {
+// 		packet.SendErrorPacket(os.Stdout, err.Error())
+// 		return
+// 	}
+// 	packetParser := packet.MakePacketParser(os.Stdin)
+// 	sender := packet.MakePacketSender(os.Stdout)
+// 	tailer, err := cmdtail.MakeTailer(sender)
+// 	if err != nil {
+// 		packet.SendErrorPacket(os.Stdout, err.Error())
+// 		return
+// 	}
+// 	go tailer.Run()
+// 	initPacket := shexec.MakeInitPacket()
+// 	sender.SendPacket(initPacket)
+// 	for pk := range packetParser.MainCh {
+// 		if pk.GetType() == packet.RunPacketStr {
+// 			doMainRun(pk.(*packet.RunPacketType), sender)
+// 			continue
+// 		}
+// 		if pk.GetType() == packet.GetCmdPacketStr {
+// 			err = doGetCmd(tailer, pk.(*packet.GetCmdPacketType), sender)
+// 			if err != nil {
+// 				errPk := packet.MakeErrorPacket(err.Error())
+// 				sender.SendPacket(errPk)
+// 				continue
+// 			}
+// 			continue
+// 		}
+// 		if pk.GetType() == packet.CdPacketStr {
+// 			cdPacket := pk.(*packet.CdPacketType)
+// 			err := os.Chdir(cdPacket.Dir)
+// 			resp := packet.MakeResponsePacket(cdPacket.ReqId)
+// 			if err != nil {
+// 				resp.Error = err.Error()
+// 			} else {
+// 				resp.Success = true
+// 			}
+// 			sender.SendPacket(resp)
+// 			continue
+// 		}
+// 		if pk.GetType() == packet.ErrorPacketStr {
+// 			errPk := pk.(*packet.ErrorPacketType)
+// 			errPk.Error = "invalid packet sent to mshell: " + errPk.Error
+// 			sender.SendPacket(errPk)
+// 			continue
+// 		}
+// 		sender.SendErrorPacket(fmt.Sprintf("invalid packet '%s' sent to mshell", pk.GetType()))
+// 	}
+// }
 
 func readFullRunPacket(packetParser *packet.PacketParser) (*packet.RunPacketType, error) {
 	rpb := packet.MakeRunPacketBuilder()
@@ -168,28 +167,24 @@ func handleSingle() {
 	}
 	runPacket, err := readFullRunPacket(packetParser)
 	if err != nil {
-		ck := base.CommandKey("")
-		if runPacket != nil {
-			ck = runPacket.CK
-		}
-		sender.SendCKErrorPacket(ck, err.Error())
+		sender.SendErrorResponse(runPacket.ReqId, err)
 		return
 	}
 	err = shexec.ValidateRunPacket(runPacket)
 	if err != nil {
-		sender.SendCKErrorPacket(runPacket.CK, err.Error())
+		sender.SendErrorResponse(runPacket.ReqId, err)
 		return
 	}
 	if runPacket.Detached {
 		err := shexec.RunCommandDetached(runPacket, sender)
 		if err != nil {
-			sender.SendCKErrorPacket(runPacket.CK, err.Error())
+			sender.SendErrorResponse(runPacket.ReqId, err)
 			return
 		}
 	} else {
 		cmd, err := shexec.RunCommandSimple(runPacket, sender)
 		if err != nil {
-			sender.SendCKErrorPacket(runPacket.CK, fmt.Sprintf("error running command: %v", err))
+			sender.SendErrorResponse(runPacket.ReqId, fmt.Errorf("error running command: %w", err))
 			return
 		}
 		defer cmd.Close()
diff --git a/pkg/packet/packet.go b/pkg/packet/packet.go
index aab905e73..dcdd5f093 100644
--- a/pkg/packet/packet.go
+++ b/pkg/packet/packet.go
@@ -19,10 +19,11 @@ import (
 	"github.com/scripthaus-dev/mshell/pkg/base"
 )
 
-// remote: init, run, ping, data, cmdstart, cmddone
-// remote(detached): init, run, cmdstart
-// server: init, run, ping, cmdstart, cmddone, cd, resp, getcmd, untailcmd, cmddata, input, data, [comp]
-// all: error, message
+// single          : <init, >run, >cmddata, >cmddone, <cmdstart, <>data, <>dataack, <cmddone
+// single(detached): <init, >run, >cmddata, >cmddone, <cmdstart
+// server          : <init, >run, >cmddata, >cmddone, <cmdstart, <>data, <>dataack, <cmddone
+//                   >cd, >getcmd, >untailcmd, >input, <resp
+// all             : <>error, <>message, <>ping, <raw
 
 var GlobalDebug = false
 
@@ -37,7 +38,7 @@ const (
 	DataEndPacketStr   = "dataend"
 	ResponsePacketStr  = "resp" // rpc-response
 	DonePacketStr      = "done"
-	ErrorPacketStr     = "error"
+	CmdErrorPacketStr  = "cmderror"
 	MessagePacketStr   = "message"
 	GetCmdPacketStr    = "getcmd"    // rpc
 	UntailCmdPacketStr = "untailcmd" // rpc
@@ -57,7 +58,7 @@ func init() {
 	TypeStrToFactory[PingPacketStr] = reflect.TypeOf(PingPacketType{})
 	TypeStrToFactory[ResponsePacketStr] = reflect.TypeOf(ResponsePacketType{})
 	TypeStrToFactory[DonePacketStr] = reflect.TypeOf(DonePacketType{})
-	TypeStrToFactory[ErrorPacketStr] = reflect.TypeOf(ErrorPacketType{})
+	TypeStrToFactory[CmdErrorPacketStr] = reflect.TypeOf(CmdErrorPacketType{})
 	TypeStrToFactory[MessagePacketStr] = reflect.TypeOf(MessagePacketType{})
 	TypeStrToFactory[CmdStartPacketStr] = reflect.TypeOf(CmdStartPacketType{})
 	TypeStrToFactory[CmdDonePacketStr] = reflect.TypeOf(CmdDonePacketType{})
@@ -325,8 +326,12 @@ func (p *ResponsePacketType) GetResponseId() string {
 	return p.RespId
 }
 
-func MakeResponsePacket(reqId string) *ResponsePacketType {
-	return &ResponsePacketType{Type: ResponsePacketStr, RespId: reqId}
+func MakeErrorResponsePacket(reqId string, err error) *ResponsePacketType {
+	return &ResponsePacketType{Type: ResponsePacketStr, RespId: reqId, Error: err.Error()}
+}
+
+func MakeResponsePacket(reqId string, data interface{}) *ResponsePacketType {
+	return &ResponsePacketType{Type: ResponsePacketStr, RespId: reqId, Success: true, Data: data}
 }
 
 type RawPacketType struct {
@@ -488,21 +493,26 @@ type BarePacketType struct {
 	Type string `json:"type"`
 }
 
-type ErrorPacketType struct {
-	Type  string `json:"type"`
-	Error string `json:"error"`
+type CmdErrorPacketType struct {
+	Type  string          `json:"type"`
+	CK    base.CommandKey `json:"ck"`
+	Error string          `json:"error"`
 }
 
-func (*ErrorPacketType) GetType() string {
-	return ErrorPacketStr
+func (*CmdErrorPacketType) GetType() string {
+	return CmdErrorPacketStr
 }
 
-func (p *ErrorPacketType) String() string {
+func (p *CmdErrorPacketType) GetCK() base.CommandKey {
+	return p.CK
+}
+
+func (p *CmdErrorPacketType) String() string {
 	return fmt.Sprintf("error[%s]", p.Error)
 }
 
-func MakeErrorPacket(errorStr string) *ErrorPacketType {
-	return &ErrorPacketType{Type: ErrorPacketStr, Error: errorStr}
+func MakeCmdErrorPacket(ck base.CommandKey, err error) *CmdErrorPacketType {
+	return &CmdErrorPacketType{Type: CmdErrorPacketStr, CK: ck, Error: err.Error()}
 }
 
 type PacketType interface {
@@ -594,8 +604,8 @@ func SendPacket(w io.Writer, packet PacketType) error {
 	return nil
 }
 
-func SendErrorPacket(w io.Writer, errorStr string) error {
-	return SendPacket(w, MakeErrorPacket(errorStr))
+func SendCmdError(w io.Writer, ck base.CommandKey, err error) error {
+	return SendPacket(w, MakeCmdErrorPacket(ck, err))
 }
 
 type PacketSender struct {
@@ -679,12 +689,18 @@ func (sender *PacketSender) SendPacket(pk PacketType) error {
 	return nil
 }
 
-func (sender *PacketSender) SendErrorPacket(errVal string) error {
-	return sender.SendPacket(MakeErrorPacket(errVal))
+func (sender *PacketSender) SendCmdError(ck base.CommandKey, err error) error {
+	return sender.SendPacket(MakeCmdErrorPacket(ck, err))
 }
 
-func (sender *PacketSender) SendCKErrorPacket(ck base.CommandKey, errVal string) error {
-	return sender.SendPacket(MakeErrorPacket(errVal))
+func (sender *PacketSender) SendErrorResponse(reqId string, err error) error {
+	pk := MakeErrorResponsePacket(reqId, err)
+	return sender.SendPacket(pk)
+}
+
+func (sender *PacketSender) SendResponse(reqId string, data interface{}) error {
+	pk := MakeResponsePacket(reqId, data)
+	return sender.SendPacket(pk)
 }
 
 func (sender *PacketSender) SendMessage(fmtStr string, args ...interface{}) error {
@@ -698,8 +714,8 @@ type UnknownPacketReporter interface {
 type DefaultUPR struct{}
 
 func (DefaultUPR) UnknownPacket(pk PacketType) {
-	if pk.GetType() == ErrorPacketStr {
-		errPacket := pk.(*ErrorPacketType)
+	if pk.GetType() == CmdErrorPacketStr {
+		errPacket := pk.(*CmdErrorPacketType)
 		// at this point, just send the error packet to stderr rather than try to do something special
 		fmt.Fprintf(os.Stderr, "[error] %s\n", errPacket.Error)
 	} else if pk.GetType() == RawPacketStr {
diff --git a/pkg/packet/parser.go b/pkg/packet/parser.go
index e8b2a96da..5d2c91e32 100644
--- a/pkg/packet/parser.go
+++ b/pkg/packet/parser.go
@@ -8,7 +8,6 @@ package packet
 
 import (
 	"bufio"
-	"fmt"
 	"io"
 	"strconv"
 	"strings"
@@ -18,6 +17,7 @@ import (
 type PacketParser struct {
 	Lock   *sync.Mutex
 	MainCh chan PacketType
+	Err    error
 }
 
 func CombinePacketParsers(p1 *PacketParser, p2 *PacketParser) *PacketParser {
@@ -46,6 +46,20 @@ func CombinePacketParsers(p1 *PacketParser, p2 *PacketParser) *PacketParser {
 	return rtnParser
 }
 
+func (p *PacketParser) GetErr() error {
+	p.Lock.Lock()
+	defer p.Lock.Unlock()
+	return p.Err
+}
+
+func (p *PacketParser) SetErr(err error) {
+	p.Lock.Lock()
+	defer p.Lock.Unlock()
+	if p.Err == nil {
+		p.Err = err
+	}
+}
+
 func MakePacketParser(input io.Reader) *PacketParser {
 	parser := &PacketParser{
 		Lock:   &sync.Mutex{},
@@ -62,8 +76,7 @@ func MakePacketParser(input io.Reader) *PacketParser {
 				return
 			}
 			if err != nil {
-				errPacket := MakeErrorPacket(fmt.Sprintf("reading packets from input: %v", err))
-				parser.MainCh <- errPacket
+				parser.SetErr(err)
 				return
 			}
 			if line == "\n" {
@@ -86,9 +99,8 @@ func MakePacketParser(input io.Reader) *PacketParser {
 			}
 			pk, err := ParseJsonPacket([]byte(line[bracePos:]))
 			if err != nil {
-				errPk := MakeErrorPacket(fmt.Sprintf("parsing packet json from input: %v", err))
-				parser.MainCh <- errPk
-				return
+				parser.MainCh <- MakeRawPacket(line[:len(line)-1])
+				continue
 			}
 			if pk.GetType() == DonePacketStr {
 				return
diff --git a/pkg/server/server.go b/pkg/server/server.go
index 2b28a19a6..fa736aa50 100644
--- a/pkg/server/server.go
+++ b/pkg/server/server.go
@@ -71,14 +71,14 @@ func (m *MServer) MakeServerFdContext(ck base.CommandKey) *serverFdContext {
 func (m *MServer) ProcessCommandPacket(pk packet.CommandPacketType) {
 	ck := pk.GetCK()
 	if ck == "" {
-		m.Sender.SendErrorPacket(fmt.Sprintf("received '%s' packet without ck", pk.GetType()))
+		m.Sender.SendMessage(fmt.Sprintf("received '%s' packet without ck", pk.GetType()))
 		return
 	}
 	m.Lock.Lock()
 	fdContext := m.FdContextMap[ck]
 	m.Lock.Unlock()
 	if fdContext == nil {
-		m.Sender.SendCKErrorPacket(ck, fmt.Sprintf("no server context for ck '%s'", ck))
+		m.Sender.SendCmdError(ck, fmt.Errorf("no server context for ck '%s'", ck))
 		return
 	}
 	if pk.GetType() == packet.DataPacketStr {
@@ -89,7 +89,7 @@ func (m *MServer) ProcessCommandPacket(pk packet.CommandPacketType) {
 		m.Sender.SendPacket(pk)
 		return
 	} else {
-		m.Sender.SendCKErrorPacket(ck, fmt.Sprintf("invalid packet '%s' received", packet.AsExtType(pk)))
+		m.Sender.SendCmdError(ck, fmt.Errorf("invalid packet '%s' received", packet.AsExtType(pk)))
 		return
 	}
 }
@@ -114,7 +114,7 @@ func (m *MServer) RemoveFdContext(ck base.CommandKey) {
 
 func (m *MServer) runCommand(runPacket *packet.RunPacketType) {
 	if err := runPacket.CK.Validate("packet"); err != nil {
-		m.Sender.SendErrorPacket(fmt.Sprintf("server run packets require valid ck: %s", err))
+		m.Sender.SendResponse(runPacket.ReqId, fmt.Errorf("server run packets require valid ck: %s", err))
 		return
 	}
 	fdContext := m.MakeServerFdContext(runPacket.CK)
@@ -125,7 +125,7 @@ func (m *MServer) runCommand(runPacket *packet.RunPacketType) {
 			m.Sender.SendPacket(donePk)
 		}
 		if err != nil {
-			m.Sender.SendCKErrorPacket(runPacket.CK, err.Error())
+			m.Sender.SendErrorResponse(runPacket.ReqId, err)
 		}
 	}()
 }
@@ -183,7 +183,7 @@ func RunServer() (int, error) {
 			server.ProcessCommandPacket(cmdPk)
 			continue
 		}
-		server.Sender.SendErrorPacket(fmt.Sprintf("invalid packet '%s' sent to mshell", packet.AsString(pk)))
+		server.Sender.SendMessage(fmt.Sprintf("invalid packet '%s' sent to mshell", packet.AsString(pk)))
 		continue
 	}
 	return 0, nil
diff --git a/pkg/shexec/shexec.go b/pkg/shexec/shexec.go
index a19edafe1..5981fdcad 100644
--- a/pkg/shexec/shexec.go
+++ b/pkg/shexec/shexec.go
@@ -906,35 +906,35 @@ func RunCommandDetached(pk *packet.RunPacketType, sender *packet.PacketSender) e
 		fmt.Printf("sender done! start: %v\n", startPacket)
 		err = unix.Dup2(int(nullFd.Fd()), int(os.Stdin.Fd()))
 		if err != nil {
-			cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot dup2 stdin to /dev/null: %w", err))
+			cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("cannot dup2 stdin to /dev/null: %w", err))
 		}
 		err = unix.Dup2(int(nullFd.Fd()), int(os.Stdout.Fd()))
 		if err != nil {
-			cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot dup2 stdin to /dev/null: %w", err))
+			cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("cannot dup2 stdin to /dev/null: %w", err))
 		}
 		err = unix.Dup2(int(nullFd.Fd()), int(os.Stderr.Fd()))
 		if err != nil {
-			cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot dup2 stdin to /dev/null: %w", err))
+			cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("cannot dup2 stdin to /dev/null: %w", err))
 		}
 		cmd.DetachedOutput.SendPacket(startPacket)
 	}()
 	ptyOutFd, err := os.OpenFile(fileNames.PtyOutFile, os.O_TRUNC|os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0600)
 	if err != nil {
-		cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("cannot open ptyout file '%s': %v", fileNames.PtyOutFile, err))
+		cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("cannot open ptyout file '%s': %w", fileNames.PtyOutFile, err))
 		// don't return (command is already running)
 	}
 	go func() {
 		// copy pty output to .ptyout file
 		_, copyErr := io.Copy(ptyOutFd, cmdPty)
 		if copyErr != nil {
-			cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("copying pty output to ptyout file: %v", copyErr))
+			cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("copying pty output to ptyout file: %w", copyErr))
 		}
 	}()
 	go func() {
 		// copy .stdin fifo contents to pty input
 		copyFifoErr := MakeAndCopyStdinFifo(cmdPty, fileNames.StdinFifo)
 		if copyFifoErr != nil {
-			cmd.DetachedOutput.SendCKErrorPacket(pk.CK, fmt.Sprintf("reading from stdin fifo: %v", copyFifoErr))
+			cmd.DetachedOutput.SendCmdError(pk.CK, fmt.Errorf("reading from stdin fifo: %w", copyFifoErr))
 		}
 	}()
 	donePacket := cmd.WaitForCommand()