Clojure how to get JVM options from inside application

(.getInputArguments (java.lang.management.ManagementFactory/getRuntimeMXBean))

Credit: How to get vm arguments from inside of java application?

Clojure has lesser typing error problems than the others well-known dynamic typing languages

Give these snippets a try.

// JS
function foo () {
  bar(1)
}

# Ruby
def foo
  bar(1)
end

; Clojure
(defn foo [] 
  (bar 1))

As you can see from the images below, Clojure doesn't allow you to refer to an undeclared symbol. I believe this takes away quite a bit of typing error issues.

Config number of file descriptors on Linux

Check file descriptor limit for a process. Vary depending on owner of the process

$ cat /proc/{process-id}/limits

Check current number of file descriptors of a process

$ sudo ls /proc/{process-id}/fd | wc -l

Set file descriptors limit for a user at /etc/security/limits.conf

*    soft nofile 64000
*    hard nofile 64000
root soft nofile 64000
root hard nofile 64000

Check system file descriptor limit

$ cat /proc/sys/fs/file-max

Check current number of system file descriptors

$ cat /proc/sys/fs/file-nr 

Credits:

• Raising the Maximum Number of File Descriptors (Open Files) on Ubuntu 14.04 Trusty
• https://unix.stackexchange.com/a/104405

Increase video volume

$ ffmpeg -i input -vcodec copy -af "volume=20dB" output

Credit: How to increase volume in a video without re-encoding the video 

Convert .ts to .mp4

$ ffmpeg -i input.ts -acodec copy -vcodec copy out.mp4

Credit: http://stackoverflow.com/a/17916418/1032449 

[PostgreSQL] How to verify if replication catch up with master change

[Run on master] Check master location with

SELECT pg_current_xlog_location();

 [Run on replica] Check replica replayed location with

SELECT pg_last_xlog_replay_location();

[Run on master] Check replica status from master

SELECT client_addr, state, sent_location, write_location, flush_location, replay_location FROM pg_stat_replication;

*write, flush, replay are status of replica

[Run on replica] Check time from the latest reply

SELECT now() - pg_last_xact_replay_timestamp() AS replication_delay;

Credit:

• Bullet 12th of https://wiki.postgresql.org/wiki/Streaming_Replication
• https://www.niwi.nz/2013/02/16/replication-status-in-postgresql/

Shorthand for Git upstream (tracked) remote branch

It's @{u}.

For example, if you are on master branch, and master branch is tracked with origin/master. You can use git merge @{u} instead of git merge origin/master.

Reference: https://git-scm.com/book/en/v2/Git-Branching-Remote-Branches#upstream-shorthand-k9UotnHmIO