IT notes


Edit environment variables: vared PATH Diff command output creating temporary normal files vimdiff =(ls /bin) =(ls /usr/bin) Print path print -l $path Run a command detached &! or &| put it in background and disown the process, exiting the shell will leave it running: sleep 300 &!

Google Cloud Functions

Testing Google Cloud Functions using go with an average of 250 requests/second. Cost per day close to $10USD Request per day: 23,511,849 Errors: 0 memory usage: 10.4MB execution time: 55.04ms

ssh wireshark

To analyze traffic remotely over ssh: ssh [email protected] sudo tcpdump -U -s0 -i pflog0 -w -| wireshark -k -i - In case need an specific port: ssh [email protected] sudo tcpdump -U -s0 -i pflog0 -w - 'port 5984' | wireshark -k -i - To ignore trafic from ssh: ssh [email protected] sudo tcpdump -U -s0 -i pflog0 -w - 'not port 22' | wireshark -k -i -

ELK delete_by_query

To delete indexes older than X days: POST haproxy/_delete_by_query { "query": { "range": { "ISODATE": { "lt": "now-3d" } } } }

openssl SHA1 HMAC

To create an HMAC-SHA1: $ echo -n "string" | openssl sha1 -hmac "shared_secret" or $ echo -n "string" | openssl dgst -sha1 -hmac "shared_secret"

DoH Firefox

Open firefox and type: about:config Search for: network.trr.uri Probably you already have: If not add it or use something like: Then enable network.trr.mode by setting it to 2 Set network.trr.mode to 2 make DNS Over HTTPS the browser’s first choice but use regular DNS as a fallback (0 is “off by default”, 1 lets Firefox pick whichever is faster, 3 for TRR only mode, 5 to explicitly turn it off).


In macOS, to find a path of an application, for example Chromium: $ osascript -e 'POSIX path of (path to application "Chromium")'


To periodically check status of the cluster, create a script (/tmp/xx): #!/bin/sh mysql --defaults-file=/path/to/.my.cnf -s -e "SHOW GLOBAL STATUS WHERE Variable_name IN ('wsrep_ready', 'wsrep_cluster_size', 'wsrep_cluster_status', 'wsrep_connected');" And run it with: watch sh /tmp/xx If single node alive (ERROR 1047 WSREP has not yet prepared node for application use): SET GLOBAL wsrep_provider_options='pc.bootstrap=YES'; This node can be used now has the new master so others nodes can recover from it.

galera alter

To prevent bloking the cluster while doing ALTERS (SCHEMA UPGRADES), do this per node: SET wsrep_OSU_method='RSU'; Then Run the ALTER statement once done reset the Schema Upgrade method back to Total Order Isolation. SET wsrep_OSU_method='TOI';

mojave Iso

Create 12 GB tmp disk: hdiutil create -o /tmp/Mojave.cdr -size 12000m -layout SPUD -fs HFS+J Attach the disk: hdiutil attach /tmp/Mojave.cdr.dmg -noverify -mountpoint /Volumes/install_build Extract the installer: sudo /Applications/Install\ macOS\ --volume /Volumes/install_build Create the iso mv /tmp/Mojave.cdr.dmg ~/Desktop/InstallSystem.dmg hdiutil detach /Volumes/Install\ macOS\ Mojave hdiutil convert ~/Desktop/InstallSystem.dmg -format UDTO -o ~/Desktop/Mojave.iso Rename Mojave.iso.cdr to Mojave.iso