☰

为什么不出现此错误：systemctl show 'random text here'.device

tag-icon • tag-icon linux systemd qubes showinfo
为什么不出现此错误：systemctl show 'random text here'.device

样本：

[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当shell 不解释 时，以下输出很好（因为它被引用了）：

[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

以下输出很糟糕，因为sys-devices-virtual-block-dmx2d0.device不存在（请注意 shell 如何删除\）：

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

以下输出是错误的，因为random text here.device不存在：

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

因此，上面两个不存在的内容.device显示了类似的通用输出，并不真正表明它们不存在（Substate=dead？）。您很容易忘记引用设备名称，并且不会出现错误，从而认为这是.device您想要查看的特定设备的真实信息。

使用 Fedora 25 的 Systemd 版本 231，在 Qubes OS 4.0 的 dom0 中：

[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

为什么 systemctl 不给出错误（并且退出代码！= 0）？

答案1

该show命令旨在由计算机（而不是用户）解析，使用等效的（但为人类定义的）命令status：

$ systemctl status 'random-text-here'.device; echo "Exit Status :$?"
● random-text-here.device
   Loaded: loaded
   Active: inactive (dead)
Exit Status :3

相关内容