HTTP(s) checks with httpstat.us & curl

Useful site for HTTP(S) testing: https://httpstat.us/

Example 1:

curl --connect-timeout 5 -m 10 https://httpstat.us/200?sleep=7000 > test.curl

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100     6    0     6    0     0      0      0 --:--:--  0:00:07 --:--:--     1

echo $?

0

Example 2:

curl --connect-timeout 5 -m 10 https://httpstat.us/200?sleep=10000 > test.curl

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:--  0:00:10 --:--:--     0

curl: (28) Operation timed out after 10001 milliseconds with 0 out of -1 bytes received

echo $?

28

Notes about timeouts in curl:

https://unix.stackexchange.com/questions/94604/does-curl-have-a-timeout/94612

Managing log rotation in Linux

 Add new file to rotation:

• copy one of /etc/logrotate.d/* configuration files to working (e.g. home) directory, name it e.g. new-file
• vim new-file
• change path to point to new (existing) file to be rotated
• change other parameters, if needed
• sudo mv new-file /etc/logrotate.d/
• sudo chown root:root /etc/logrotate.d/new-file

Dry run:

logrotate -d /etc/logrotate.d/new-file

Forced rotation:

sudo logrotate -vf /etc/logrotate.d/new-file

More info:

man logrotate
https://www.tecmint.com/install-logrotate-to-manage-log-rotation-in-linux/

Bash tips I

Inputs to functions:

https://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-8.html

Outputs from functions:

https://www.linuxjournal.com/content/return-values-bash-functions

Check for empty variable:

https://www.cyberciti.biz/faq/unix-linux-bash-script-check-if-variable-is-empty/

Keyboard shortcuts:

http://teohm.com/blog/shortcuts-to-move-faster-in-bash-command-line/

4 ways to search and replace with regular expressions

 See here.

Bonus: grep for literal strings

How to analyze active cron jobs in CentOS 7

 sudo cat /var/log/cron | cut -d ' ' -f 6- | sort | uniq -c | sort -nr

Statistical analysis of MySQL/MariaDB slow queries

One-liner:

sudo grep -e '^select' -e '^insert' -e '^update' -e '^delete' /srv/data/mysql/mysql_slow.log | cut -d ' ' -f 1-3 | sort | uniq -c | sort -nr | head

How to extract raw value from JSON and cut it into pieces by size

Sample data:

{
  "var_name1": {},
  "var_name2": "string",
  "var_name3": "long string",
  "var_name4": 15
}

Fill Bash variable with extracted long string raw value from JSON:

VAR_NAME=`cat file.json | jq --raw-output '.var_name3'`

Then reference "chunks" of data using Bash variable index modifiers, e.g. by 255 characters:

• ${VAR_NAME:0:255}
• ${VAR_NAME:255:255}
• ${VAR_NAME:510:255}
• ${VAR_NAME:765:255}
• ${VAR_NAME:1020:255}

One-liner alternative extracting and displaying output in single command line:

VAR_NAME=`cat file.json  | jq --raw-output '.var_name3'` ; echo $VAR_NAME ; echo ${VAR_NAME:0:255} ; echo ${VAR_NAME:255:255} ; echo ${VAR_NAME:510:255} ; echo ${VAR_NAME:765:255} ; echo ${VAR_NAME:1020:255}

How to check website availability for various users

https://www.isitdownrightnow.com/

https://downforeveryoneorjustme.com/