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--- linux [2023/12/17 19:39] – nine
+++ linux [2025/01/09 06:28] (current) – nine
@@ Line 14: / Line 14: @@
   iptables -A prometheus -j DROP
   iptables -I INPUT -m tcp -p tcp --dport 9100 -j prometheus
+===== docker =====
+open shell in a running container
+  docker exec -ti <container-name> /bin/bash
+===== email =====
+==== sender guidelines ====
+  - https://support.google.com/a/answer/14229414
+  - https://senders.yahooinc.com/best-practices/
+  - https://senders.yahooinc.com/faqs/
+  - https://www.bsi.bund.de/dok/TR-03182
+==== pdf ====
+default:
+  ps2pdf input.pdf output.pdf
+ghostscript options -dPDFSETTINGS
+  ps2pdf -dPDFSETTINGS=/ebook input.pdf output.pdf
+possible options:
+  -dPDFSETTINGS=/screen 	(72 dpi)
+  -dPDFSETTINGS=/ebook 	(150 dpi)
+  -dPDFSETTINGS=/prepress (300 dpi)
+  -dPDFSETTINGS=/printer 	(300 dpi)
+  -dPDFSETTINGS=/default 	Selects the output which is useful for multiple purposes. Can cause large PDFS.
+===== Video =====
+compress video for email sending
+  ffmpeg -i input.mp4 output_compressed.mp4
+adjust volume
+  ffmpeg -i input.avi -af "volumedetect" -vn -sn -dn -f null /dev/null
+gives:
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] n_samples: 1839104
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] mean_volume: -43.4 dB
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] max_volume: -31.5 dB
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] histogram_31db: 64
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] histogram_32db: 455
+  [Parsed_volumedetect_0 @ 0x55f12ff28780] histogram_33db: 1884
+increase max volume:
+  ffmpeg -i input.avi -af "volume=30dB" -c:v copy -c:a libmp3lame -q:a 2 output.mp4
+flip image
+  ffmpeg -i input.mp4 -vf "transpose=2" output.mp4
+transpose options:
+= 90° counter-clockwise and vertical flip (default)
+= 90° clockwise
+= 90° counter-clockwise
+= 90° clockwise and vertical flip