このエラーが発生しない理由は、systemctl show 'random text here'.deviceです。

サンプル:

[ctor@dom0 ~]$ cat nonsense 
#!/bin/bash

set -vex
systemctl show "sys-devices-virtual-block-dm\x2d0.device"
echo 
systemctl show sys-devices-virtual-block-dm\x2d0.device
echo 
systemctl show 'random text here'.device
echo 

\x2dシェルで解釈されない場合は、次の出力は問題ありません（引用されるため）。

[ctor@dom0 ~]$ ./nonsense 
systemctl show "sys-devices-virtual-block-dm\x2d0.device"
+ systemctl show 'sys-devices-virtual-block-dm\x2d0.device'
SysFSPath=/sys/devices/virtual/block/dm-0
Id=sys-devices-virtual-block-dm\x5cx2d0.device
Names=sys-devices-virtual-block-dm\x5cx2d0.device
Wants=lvm2-pvscan@253:0.service
Description=/sys/devices/virtual/block/dm-0
LoadState=loaded
ActiveState=active
SubState=plugged
StateChangeTimestamp=Sun 2018-09-09 15:49:14 CEST
StateChangeTimestampMonotonic=10072227
InactiveExitTimestamp=Sun 2018-09-09 15:49:14 CEST
InactiveExitTimestampMonotonic=10072227
ActiveEnterTimestamp=Sun 2018-09-09 15:49:14 CEST
ActiveEnterTimestampMonotonic=10072227
ActiveExitTimestampMonotonic=0
InactiveEnterTimestampMonotonic=0
CanStart=no
CanStop=no
CanReload=no
CanIsolate=no
StopWhenUnneeded=no
RefuseManualStart=no
RefuseManualStop=no
AllowIsolate=no
DefaultDependencies=yes
OnFailureJobMode=replace
IgnoreOnIsolate=yes
NeedDaemonReload=no
JobTimeoutUSec=30s
JobTimeoutAction=none
ConditionResult=no
AssertResult=no
ConditionTimestampMonotonic=0
AssertTimestampMonotonic=0
Transient=no
StartLimitIntervalSec=10000000
StartLimitBurst=5
StartLimitAction=none
echo 
+ echo

次の出力はsys-devices-virtual-block-dmx2d0.device存在しないため、無効な出力です（シェルからそれらを削除する方法を参照\）。

systemctl show sys-devices-virtual-block-dm\x2d0.device
+ systemctl show sys-devices-virtual-block-dmx2d0.device
Id=sys-devices-virtual-block-dmx2d0.device
Names=sys-devices-virtual-block-dmx2d0.device
Description=sys-devices-virtual-block-dmx2d0.device
LoadState=loaded
ActiveState=inactive
SubState=dead
StateChangeTimestampMonotonic=0
InactiveExitTimestampMonotonic=0
ActiveEnterTimestampMonotonic=0
ActiveExitTimestampMonotonic=0
InactiveEnterTimestampMonotonic=0
CanStart=no
CanStop=no
CanReload=no
CanIsolate=no
StopWhenUnneeded=no
RefuseManualStart=no
RefuseManualStop=no
AllowIsolate=no
DefaultDependencies=yes
OnFailureJobMode=replace
IgnoreOnIsolate=yes
NeedDaemonReload=no
JobTimeoutUSec=30s
JobTimeoutAction=none
ConditionResult=no
AssertResult=no
ConditionTimestampMonotonic=0
AssertTimestampMonotonic=0
Transient=no
StartLimitIntervalSec=10000000
StartLimitBurst=5
StartLimitAction=none
echo 
+ echo

次の出力はrandom text here.device存在しないため無効です。

systemctl show 'random text here'.device
+ systemctl show 'random text here.device'
Id=random\x5cx20text\x5cx20here.device
Names=random\x5cx20text\x5cx20here.device
Description=random\x5cx20text\x5cx20here.device
LoadState=loaded
ActiveState=inactive
SubState=dead
StateChangeTimestampMonotonic=0
InactiveExitTimestampMonotonic=0
ActiveEnterTimestampMonotonic=0
ActiveExitTimestampMonotonic=0
InactiveEnterTimestampMonotonic=0
CanStart=no
CanStop=no
CanReload=no
CanIsolate=no
StopWhenUnneeded=no
RefuseManualStart=no
RefuseManualStop=no
AllowIsolate=no
DefaultDependencies=yes
OnFailureJobMode=replace
IgnoreOnIsolate=yes
NeedDaemonReload=no
JobTimeoutUSec=30s
JobTimeoutAction=none
ConditionResult=no
AssertResult=no
ConditionTimestampMonotonic=0
AssertTimestampMonotonic=0
Transient=no
StartLimitIntervalSec=10000000
StartLimitBurst=5
StartLimitAction=none
echo 
+ echo

したがって、存在しない上記の2つは.device同様の一般的な出力を示し、実際には存在しないことを示していません（Substate=dead？）。デバイス名を引用するのを忘れやすく、これが.device見たい特定のデバイスに関する実際の情報だと思う間違いを犯さないようにします。

Qubes OS 4.0のdom0でFedora 25のSystemdバージョン231を使用する：

[ctor@dom0 ~]$ systemctl --version
systemd 231
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN

systemctlでエラー（および終了コード！= 0）が発生しないのはなぜですか？