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Workshop » Reference Section » Grimoires » IT » Platforms » MacOS » Networking

SSH into local mac, error “WARNING- REMOTE HOST IDENTIFICATION HAS CHANGED!”

SSHing into a local MacOS machine at address "macbook.local", I suddenly got this:

[code]@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has just been changed. The fingerprint for the ED25519 key sent by the remote host is SHA256:oKCEu3pDdq7xBhSPZwOzR2q0eWTvfphtvn3D4Bjz8v4. Please contact your system administrator. Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message. Offending ECDSA key in /Users/username/.ssh/known_hosts:147 Host key for macbook.local has changed and you have requested strict checking. Host key verification failed.[/code]

The solution was to run ssh-keygen -R macbook.local then try the ssh again. Then it asked me whether or not to accept the key, instead of rejecting it:

[code]$ ssh username@macbook.local The authenticity of host 'macbook.local (fe80::1890:fd32:c304:69cd%en0)' can't be established. ED25519 key fingerprint is SHA256:oKCEu3pDdq7xBhSPZwOzR2q0eWTvfphtvn3D4Bjz8v4.…
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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » PHP

Enable PHP 8.4 in Apache on Debian

According to the installer, to enable PHP 8.4 FPM in Apache2 do:
a2enmod proxy_fcgi setenvif
a2enconf php8.4-fpm

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot

How to backup a WordPress site via SSH

To make a complete local backup of a remote WordPress install over SSH, you need to perform two distinct steps:

  1. Download the files (using rsync).
  2. Export and download the database (using mysqldump piped through ssh).

Here is the step-by-step guide.

Prerequisites
  • SSH Access: You need the username, host (IP or domain), and password (or SSH key) for the remote server.
  • WordPress Path: You need to know where WordPress is installed (e.g., /var/www/html or /home/user/public_html).
  • Database Credentials: You will need the database name, user, and password. (I will show you how to find these below).
Step 1: Find Database Credentials (Optional)

If you don't know your database login details, run this command to read them from your remote wp-config.php file: ssh user@remote-server.com "cat /path/to/wordpress/wp-config.php" | grep 'DB_'

Note the DB_NAME, DB_USER, and DB_PASSWORD for Step 2.

Step 2: Download the Database (SQL Dump)…
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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » n8n
Posted inIT Grimoire

Starting a temporary instance of N8N accessible via IPv4 over the local network

N8n by default binds to localhost, and even binding it to listen on all interfaces, it still by default listens only for IPv6. You also may want to tell it to not use the Secure Cookie if you don't want to set up an SSL certificate or sign up for their cloud service. Make sure you only have it reachable on the local network if you do this, you don't want to open your instance to the entire world.

N8N_SECURE_COOKIE=false N8N_HOST=0.0.0.0 N8N_LISTEN_ADDRESS=0.0.0.0 npx n8n

Remember to open port 5678 on the machine's firewall if necessary.

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » SQL
Posted inIT Grimoire

SQL query to list all WordPress post revisions for archiving

Here's the SQL query to get all post revisions, which I do prior to cleaning them out of the database, which seems to make it much faster:

SELECT p.*
FROM [posts table name] p
WHERE (p.post_type = 'post' OR p.post_type = 'page') -- Include posts/pages
AND (p.post_date BETWEEN '2020-01-01' AND '2029-07-01') -- Adjust date range
OR (p.post_type = 'revision' AND p.post_parent IN (
SELECT ID FROM [posts table name]
WHERE post_date BETWEEN '2024-01-01' AND '2024-07-01'
));

To get just a count of revisions, change SELECT p.* to SELECT count(*).

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot
Posted inIT Grimoire

Speeding up rsnapshot (rsync) backups by removing wildcard paths from exclude

I removed a bunch of wildcard paths from rsnapshot.conf's exclude, and suddenly tonight my backup ran in a few minutes instead of taking over a day like it usually does.

Interesting, I've been looking off and on for at least the better part of a year for ways to lighten the load of rsnapshot's under-the-hood rsync backup commands, which reliably took up about half my CPU power almost continuously, and never found this tip before. You can see, plenty of wildcard paths removed, plus a few other things.

Here's a diff, rsnapshot.conf before changes (<) vs after (>):
< verbose 1
---
> verbose 4
120c120
< loglevel 2
---
> loglevel 4
143a144,146
> rsync_short_args -Wa
> #-W is transfer whole files without prescan, recommended for performance by https://serverfault.com/questions/639458/rsync-taking-100-of-cpu-and-hours-to-complete
> #NOTE: if you set the above short…

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Workshop » Reference Section » Grimoires » IT » Troubleshooting log » Web Server
Posted inIT Grimoire

Performance troubleshooting & settings changes 2025aug29

Following several days of frequent freezes, I tried changing the following settings

updated in :

[opcache] original settings
;recommended by https://vpsfix.com/14433/virtualmin-post-installation-configuration-and-server-optimization-guide/
opcache.enable=
opcache.memory_consumption=
opcache.interned_strings_buffer=
opcache.max_accelerated_files=
opcache.validate_timestamps=
opcache.revalidate_freq=
opcache.save_comments=
;end recommendation

to

[opcache]
;recommended by https://vpsfix.com/14433/virtualmin-post-installation-configuration-and-server-optimization-guide/
opcache.enable=
opcache.memory_consumption=
opcache.interned_strings_buffer=
opcache.max_accelerated_files=
opcache.validate_timestamps=
opcache.revalidate_freq=
opcache.save_comments=

-
added var_dump(opcache_get_status()) to php status page to be able to monitor opcache usage

-
changed warning logs from E_ALL & ~E_DEPRECATED & ~E_STRICT to
----
noticed contained a LOT of processes being stopped for tracing
turned off request_slowlog_timeout by setting to 0s in
had been 4s
---
I had turned on lightspeed at 1:45 am est , aug 26. Seems like more problems since then.

None of the above seem to help, still getting freezes maybe every 30 minutes. Next…

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » File management
Posted inIT Grimoire

Directory and File Locations particular to this server

PHP config -
Includes:
- opcache settings
- error warnings

PHP slow log setup is in

PHP log -

PHP error and slow logs by pool are in

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot
Posted inIT Grimoire

Resolving an rsnapshot error — “rsync: –delete does not work without –recursive (-r) or –dirs (-d). rsync error: syntax or usage error (code 1) at main.c(1795)”

I discovered rsnapshot hadn't run in a few days. Checking /etc/rsnapshot.log, I found every recent day had this: 

rsync: --delete does not work without --recursive (-r) or --dirs (-d). rsync error: syntax or usage error (code 1) at main.c(1795) [client=3.2.7]

A few days ago I had added the line rsync_short_args -W to /etc/rsnapshot.conf in an effort to get rsync to run without putting such a load on my system. Removing this and running rsnapshot -v hourly from the command line shows that without it, the first line of the rsync command was /usr/bin/rsync -ax --delete --numeric-ids --relative --delete-excluded \, but with it, the first line was /usr/bin/rsync -Wx --delete --numeric-ids --relative --delete-excluded \.

Changing the line rsync_short_args -W to rsync_short_args -Wa, with an a flag explicitly included, solved the problem. Apparently specifying custom short flags overrides at least one of the default flags.

Also: remember, when you run an…

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot
Posted inIT Grimoire

Post-migration steps when migrating or restoring Linux from backup

There are intentionally vague broad steps, here just as a reminder to myself; best to look specific instructions for each of these steps up at restore time for the particular system you're restoring to.

A.) Backups should include all user data. Depending on who you ask, that's either:
1.) The entire filesystem except /dev/*, /proc/*, /sys/*, /tmp/*, /run/*, /mnt/*, /media/*, /lost+found (which can be pulled from a complete filesystem backup with rsync -avhP --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} /mnt/olddrive/ /mnt/netdrive/)
2.)/home, /etc (except /etc/passwd and /etc/groups, these have useful information to back up but may conflict if written to a new install), /usr/local, /opt, /root, /var (exluding /var/tmp, /var/run/, /var/lock, or /var/spool except you DO want /var/spool/cron/crontabs/)

B.) After copying all the above to the new or restored disk, you need to update /etc/fstab with the new disk UUIDs.

C.) Install GRUB Bootloader.

D.) If you're using LUKS encryption, set that…

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot
Posted inIT Grimoire

Fastest way to delete a large, deep directory in Linux

Per numerous references around the web, to delete /path/to/directory-to-delete/:

 cd /path/to/ mkdir empty_dir rsync -a --delete empty_dir/ directory-to-delete/ rm -r empty_dir rm -r directory-to-delete

Disclaimer: this is for my own reference, not recommended for your use. Use it at your own risk. If I am wrong—and I may be—these commands can do tremendous damage to your system.

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » rsync & rsnapshot
Posted inIT Grimoire

Reducing rsnapshot or rsync resource usage

I've had sporadic problems with clearing the WP cache causing the server to return 520 errors for a few minutes. Usually other sites on the same server are fine, it's specific to this vhost. Logging in via SSH, checking with htop, rsync is usually hogging most of the cpu. Restarting the fpm and then restarting Apache restores the website.

According to https://www.claudiokuenzler.com/blog/361/rsnapshot-backup-reduce-high-load-with-ionice, the big bottleneck with rsync, which rsnaphot runs on, is i/o, not cpu, and rsync can actually tie up i/o such that a web server won't respond to http requests. This can be solved by making the rsnapshot command in crontab ionice -c 3 [rsnapshot command] instead of just the rsnapshot command, which tells rsync not to wait until the disk is idle before trying to access it. So I did. In fact, I made it nice -n 19 ionice -c 3 [rsnapshot command] although…

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » Git
Posted inIT Grimoire

Force Git to overwrite local changes if there is a branch conflict

Use code you find here at your own risk! I am not responsible if you damage your data or system by following any instructions you find here.

  1. Navigate to your plugin's root directory:

    Bash

    cd /home/kupietzc/public_html/kartscode/wp-content/plugins/ktwp-draggable-elements

  2. Fetch the latest changes from GitHub:
    Bash

    git fetch origin

  3. Perform a hard reset to match GitHub's main branch (assuming main is your branch):

    Bash
    git reset --hard origin/main

    WARNING: This command is destructive. It will discard all local changes to tracked files and make your local repository exactly match your GitHub repository. Ensure you have a backup of any local modifications you wish to preserve that are NOT on GitHub before running this.

  4. Clean up any untracked files or directories (remnants from manual copying):
    …
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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » PHP
Posted inIT Grimoire

How to monitor RAM for tuning pm.max_children

How to monitor RAM usage:

  1. free -h:

    • This command shows your system's total, used, and free memory in a human-readable format.
    • Key metrics:
      • total: Total RAM.
      • used: RAM currently in use.
      • free: Unused RAM.
      • buff/cache: RAM used for file system buffers and page cache. This is good; Linux uses free RAM for this and frees it when applications need it.
      • available: The most important metric. This estimates how much memory is available for starting new applications without swapping.
    • Run it before and after: Run free -h before you increase max_children and then after your server has been running for a while under typical load with the new settings. Compare the available memory.

  2. htop (recommended if installed):

    • htop (you might need to sudo…
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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » cron
Posted inIT Grimoire

Add sar logging for CPU, RAM, and disk I/O

Add or change /etc/cron.d/sysstat to this. This creates a cron jobe to write file /tmp/outage_resource_log.txt that keeps minute-by-minute stats, sometimes useful in troubleshooting slowdowns. However, it's not a great way to do things, it create a small, constant resource drag, so disable it when done troubleshooting.

# The first element of the path is a directory where the debian-sa1
# script is located
PATH=/usr/lib/sysstat:/usr/sbin:/usr/sbin:/usr/bin:/sbin:/bin

# Activity reports every 10 minutes everyday
#ORIGINAL DEFAULT WAS 5-55/10 * * * * root command -v debian-sa1 > /dev/null && debian-sa1 1 1
#uncomment above line and comment out /tmp/outage_resource_log.txt lines to restore original functionality
* * * * * root date +"%Y-%m-%d %H:%M:%S" >> /tmp/outage_resource_log.txt
* * * * * root sar -u 1 1 >> /tmp/outage_resource_log.txt 2>&1
* * * * * root sar -r 1 1 >> /tmp/outage_resource_log.txt 2>&1
* * *…

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » Apache
Posted inIT Grimoire

Add /fpm-status page to Apache virtual host

Add this to virtual host file in /etc/apache2/sites-available/, right below DocumentRoot, in both :80 and :443 sections



SetHandler "proxy:unix:/var/php-fpm/170027027353667.sock|fcgi://127.0.0.1"
Require all granted

May need in /etc/php/8.2/fpm/pool.d/www.conf, not sure:
pm.status_path = /fpm-status

May need at very start of .htaccess to prevent wordpress from intercepting the URL, not sure:
RewriteRule ^fpm-status$ - [L]

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » Apache
Posted inIT Grimoire

View last 200 lines of all access logs on apache server

find [path/to/access/logs/folder] -name "*_access_log" -exec sh -c 'tail -200 "$1" | grep -v "HetrixTools\|ok\.txt\|canary" | sed "s/$/ [$(basename "$1" _access_log)]/"' _ {} \; | sort -k4,4

The grep -v "HetrixTools\|ok\.txt\|canary" filters out hits from my uptime monitor.

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Workshop » Reference Section » Grimoires » IT » Platforms » Linux » Packages » fail2ban
Posted inIT Grimoire

How to check Fail2ban log

Command to check fail2ban's log is sudo tail -f /var/log/fail2ban.log

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Linux
Posted inIT Grimoire

Linux PHP tuning utilities & commands

1. See memory consumed by php-fpm8.2 (change this to match different PHP version if necessary)

ps --no-headers -o "rss,cmd" -C php-fpm8.2 | awk '{ sum+=$1 } END { printf ("%d%s\n", sum/NR/1024,"M") }'

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Linux
Posted inIT Grimoire

Linux SQL Tuning Utilities

1. tuning-primer.sh

Run from Github:
curl -L https://raw.githubusercontent.com/BMDan/tuning-primer.sh/main/tuning-primer.sh | bash

2. MySQLTuner.pl

wget http://mysqltuner.pl/ -O mysqltuner.pl
wget https://raw.githubusercontent.com/major/MySQLTuner-perl/master/basic_passwords.txt -O basic_passwords.txt
wget https://raw.githubusercontent.com/major/MySQLTuner-perl/master/vulnerabilities.csv -O vulnerabilities.csv
perl mysqltuner.pl --host 127.0.0.1 --user [user] --pass [pass]

Remember to quote any punctuation or BASH tokens in the password.

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