Computing

Computers and information management topics

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Category: Computing
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Some commands that aid with managing the mail queue in Postfix.

Show mail queue size:

mailq

or

postqueue -p

Show queue domain and age:

qshape

qshape deferred

-s Display the sender domain distribution instead of the recipient domain distribution

Queues:

deferred
recipients delivery failed for a transient reason (it might succeed later), the message is placed in the "deferred" queue
active
Messages in the "active" queue are ready to be sent (runnable), but are not necessarily in the process of being sent (running)
incoming
All new mail entering the Postfix queue is written into the "incoming" queue
hold
Administrator defined rules place messages into the "hold" queue and stay there until the administrator intervenes
maildrop
Messages that have been submitted via the sendmail command, but not yet brought into the main queue, await processing in the "maildrop" queue

Purge a single email:

postsuper -d [message id]

Purge all emails:

postsuper -ALL

 

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Category: Computing
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To configure various audio programs it is common that you will need the device name or some other designation. But, if you have multiple audio devices, which is increasingly common (sound on mother board, sound card, USB mic, USB camera with mic, external DAC, etc), how do you get a list?

To list the ALSA audio hardware:

aplay -l

**** List of PLAYBACK Hardware Devices **** 
card 1: C2 [Cambridge Audio DAC100 USB 2], device 0: USB Audio [USB Audio] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0 
card 2: HDMI [HDA Intel HDMI], device 3: HDMI 0 [HDMI 0] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0 
card 2: HDMI [HDA Intel HDMI], device 7: HDMI 1 [HDMI 1] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0 
card 2: HDMI [HDA Intel HDMI], device 8: HDMI 2 [HDMI 2] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0 
card 2: HDMI [HDA Intel HDMI], device 9: HDMI 3 [HDMI 3] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0 
card 3: PCH [HDA Intel PCH], device 0: ALC662 rev3 Analog [ALC662 rev3 Analog] 
  Subdevices: 1/1 
  Subdevice #0: subdevice #0

In the above list, I am seeking to use the "Cambridge DAC" so would choose hw:1,0. However, USB devices might not get the same device numbers each time they're plugged in or when the computer reboots. So, the "hw:X,Y" device shown above might change. To solve this consider using the device alias rather than the hardware listing.

To list the audio device aliases:

aplay -L

hw:CARD=C2,DEV=0 
    Cambridge Audio DAC100 USB 2, USB Audio 
    Direct hardware device without any conversions 
plughw:CARD=C2,DEV=0 
    Cambridge Audio DAC100 USB 2, USB Audio 
    Hardware device with all software conversions
iec958:CARD=C2,DEV=0 
    Cambridge Audio DAC100 USB 2, USB Audio 
    IEC958 (S/PDIF) Digital Audio Output

In the above output list "IEC958" is a standard defining digital connections for consumer electronics based on S/PDIF. This can be the best choice to use for an external (high quality) device. So, I would use iec958:CARD=C2,DEV=0.

To list pulse audio sources:

pactl list short sources

And to list pulse audio sinks:

pactl list short sinks

which shows the device name "alsa_output.usb-Cambridge_Audio_Cambridge_Audio_DAC100_USB_2_0000-00.analog-stereo".

I use this information in an audio application's configuration file. For example, in MPD I edit the mpd.conf audio output section:

audio_output {
    type "alsa"
    name "My ALSA output"
    device "iec958:CARD=Intel,DEV=0"
    mixer_control "PCM"
}

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Category: Computing
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In versions up to 3.10.2, all weblinks are listed in a category by id ordering. That is the order as shown in the "ordering" administrator view. I would like them listed by default in alphabetical title order. There does not seem to be any option for this sort order. So I have implemented the following code change.

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Category: Computing
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Two commands are most useful for managing services on a Ubuntu Linux computer; service and systemctl.

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Category: Computing
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A properly formed URL can instruct Piwigo to generate a re-sized image. The structure is as follows: